Advantages of the Use of Postbiotics in Poultry Production: A New Concept

ABSTRACT

The use of antibiotics has been prohibited in many countries of the world, in response to concerns over the health and welfare concerns of humans and animals. For this reason, scientists have been working on antibiotic alternatives capable of enhancing the productivity and immunity of poultry birds against diseases, as well as the production of healthy and economical poultry meat and eggs. Various alternatives exist and have been used for several decades, such as probiotics, prebiotics, phytobiotics, essential oils, antimicrobial peptides, organic acids, and synbiotics. A relatively new term, “postbiotic,” is used to refer to cell-free supernatants, metabiotics, biogenics, or simply metabolites. It has been suggested that postbiotics are non-viable bacterial products or metabolic byproducts secreted from probiotic microorganisms that have biologic activity in the host. While probiotics are sensitive to heat and oxygen, postbiotics are stable during industrial processing and storage. Postbiotics enhance poultry growth, improve feed efficiency, reduce intestinal pathogens, and promote overall health, making them valuable contributions for sustainable poultry production. They have many important biological properties, such as promoting immunomodulatory, antioxidant, and anti-inflammatory responses. Postbiotics improve intestinal villi, intestinal barrier functions, increase lactic acid production, and reduce Enterobacteriaceae and fecal pH, all of which lead to better immune reaction and health of the gut, as well as superior growth performance. Similarly, postbiotics reduce the plasma cholesterol and triglyceride levels in birds. This review article presents the most recent research investigating the beneficial effects of postbiotics in poultry.

Keywords:
Antioxidant and blood biochemistry; growth and meat quality; gut health and immunity; poultry; postbiotics

INTRODUCTION

Antibiotics as growth promoters have brought about important achievements in poultry production output worldwide (Mehdi et al., 2018). Antibiotic usage in animal feeds has brought about a change in intestinal flora of chickens, and influenced their immunity with an increased capacity to control diseases (Lee et al., 2012). However, the uncontrolled and indiscriminate usage of antibiotics has resulted in antibiotic-resistant bacteria and an increased incidence of antibiotics residues in animal products, causing harmful effects on the health of animals and consumers (Diarra et al., 2007; Ronquillo & Hernandez, 2017). Therefore, a ban on antibiotics usage in animal feeds has been imposed among European countries and most other countries in the world. Hence, significant efforts have been made to find safer replacements for antibiotics with the same or better effects on animal production (Diarra & Malouin, 2014). Several antibiotic substitutes in livestock production (e.g. prebiotics, probiotics, symbiotics, and postbiotics) have recently been extensively investigated (Loh et al., 2014). Probiotics are defined as a viable microorganism, of which a sufficient amount reaches the intestine in an active state and thus exerts positive health effects (Loh, 2017). Probiotics are a natural microbial population with antimicrobial activity (Rasko & Sperandio, 2010). Probiotics can also be defined as direct-fed microbials (DFM) that confer health benefits on the host administered (Khalighi et al., 2016). They can either be a single one or a mixture of the culture of living nonpathogenic microorganisms. Some mechanisms of action of probiotics include causing competitive exclusion, promoting gut maturation and integrity, regulating the immune system, preventing inflammation, improving growth, providing metabolism, and improving the fatty acid profile and oxidative stability in fresh meat (Hossain et al., 2012). Despite the numerous health benefits that probiotics provide to host animals in combating diseases, there are some problems in feeding live (viable) probiotic cells. Notably, the viability of microbes depends on certain storage requirements, as many probiotic bacteria lose their desired viability during storage (Nayak, 2010). Probiotics’ abilities to colonize and persist in the gastrointestinal tracts (GIT) varies per host. Therefore, getting a suitable strain of probiotics for each host poses practical problems (Adams, 2010). Another important issue to note is the timing of their application, an important aspect in microbe colonization, which is temporary (Balcázar et al., 2006). Furthermore, there is a high possibility of horizontal transfer of virulent genes from pathogenic microbes to probiotic bacteria in the host (Marteau & Shanahan, 2003; Newaj-Fyzul et al., 2014). This is why there has been a considerable shift towards metabolic by-products of probiotics, known as “postbiotics”, which are preferred substitutes for probiotics. Postbiotics are defined as a “preparation of inanimate microorganisms and/or their components that confers a health benefit on the host” (Salminen et al., 2021). This is a consensus definition proposed by the International Scientific Association of Probiotics and Prebiotics (ISAPP) in 2021 to replace several previous inconsistent definitions. ISAPP defines postbiotics as follows: (i) “soluble factors (products or metabolic byproducts) secreted by live bacteria, or released after bacterial lysis, such as enzymes, peptides, teichoic acids, peptidoglycan-derived muropeptides, polysaccharides, cell-surface proteins, and organic acids”; (ii) “non-viable metabolites produced by microorganisms that exert biological effects on the hosts”; (iii) “compounds produced by microorganisms, released from food components or microbial constituents, including non-viable cells that, when administered in adequate amounts, promote health and wellbeing” (Salminen et al., 2021). Many terms have been used to name nonliving forms of probiotics in recent years, including postbiotics, pseudo-probiotic, ghost probiotics, paraprobiotic, metabiotic, abiotic, cell-free supernatant, and biogenic (Louis et al., 2014). Among these, “postbiotic” is more commonly used. However, ‘paraprobiotic’ and ‘pseudoprobiotic’ have also been used in a number of studies (Hills et al., 2019). In general, postbiotics show all the beneficial effects of probiotics, including strengthening the immune system, hypersensitivity, and antibacterial, antiviral, antioxidant, antiobesity, anti-diabetes, antihypertensive, antiproliferation, anti mutation, and anticancer effects, all of which have been proven both invitro and in vivo (Martin-Gallausiaux et al., 2021). In experimental and preclinical studies, no adverse effects (such as inflammation) of postbiotics have been observed. Therefore, postbiotics can be a safe alternative to probiotics, owing to their known chemical structures, safe dose, and longer shelf life (Adela et al., 2000). Postbiotics produced from Lactobacillus plantarum increased body weight, body weight gain, feed conversion ratio, intestinal villus height, immune response, insulin-like growth factor -1(IGF-1), growth hormone receptor (GHR) mRNA expression, nonpathogenic bacteria population in the cecum, and reduced the Enterobacteriaceae and E. coli population in heat-stressed broilers, while also having high antioxidant activity (Izuddin et al., 2020). Humam et al. (2020) reported that dietary supplementation of different postbiotics mitigates adverse impacts of heat stress by increasing antioxidant enzyme activity, total antioxidant capacity, acute phase protein expression, and HSP70 expression in broilers. Other studies reported that chickens fed with probiotics showed an increase in intestinal epithelial integrity through an increase in mucin mRNA expression (Smirnov et al., 2005; Aliakbarpour et al., 2012). Moreover, improvements in broiler meat quality, and reduction in plasma cholesterol levels have been observed with dietary supplementation of postbiotics in broilers (Kareem et al., 2016).

The purpose of this review is to provide an overview of the mechanism of action of postbiotics and their impact on the growth performance, meat quality, immune system, blood biochemical profile, antioxidant status, and intestinal health of poultry birds, as well as their effect on the food safety and biopreservation of poultry products.

WHY ALTERNATIVES TO ANTIBIOTICS?

The mounting consumer awareness about the importance of safe and wholesome food, particularly of animal origin, has led to a surge in demand for naturally-sourced food products, and the application of nutraceuticals in animal husbandry (Park et al., 2016). For over six decades, dietary or in-feed antibiotics (IFA) have been extensively employed in the poultry industry for therapeutic and prophylactic purposes, as well as for promoting growth and improving feed efficiency (Gadde et al., 2018). The use of IFA or antibiotic growth promoters (AGPs) in poultry has been associated with an average growth increment rate of 3-5%, and improved feed efficiency (Dahiya et al., 2006). However, the use of antibiotics in poultry production has given rise to significant public health concerns, including the presence of drug residues in poultry products, the emergence and dissemination of antibiotic-resistant bacterial strains, gut microflora dysbiosis, and hypersensitivity, among others (Gaggia et al., 2010; Nhung et al., 2017). In response to these issues, the European Union banned the use of AGPs in 2005 (EPC, 2005), followed by restrictions in the United States and other countries (Zaidi et al., 2015; Editors, 2017). Nevertheless, the prohibition or limitation of AGPs in poultry production has resulted in increased feed intake with reduced feed efficiency, decreased body weight, compromised growth performance, higher morbidity and mortality rates, heightened risks of poultry contamination, increased production costs, and the associated economic losses (Park et al., 2016; Alsudani, 2018). Consequently, poultry farmers have turned to therapeutic antibiotics solely for disease control and prevention, leading to a potential escalation of bacterial resistance (Founou et al., 2016). To achieve sustainable antibiotic-free poultry production, an effective feeding program is crucial. Poor-quality feed additives or supplements, mycotoxin contamination, and rancid animal by-products in the feed can severely damage gut health and intestinal epithelium. Thus, high-quality feed additives play a critical role in maintaining optimal gut health and flock health. Consequently, there is a growing interest in exploring novel, cost-effective, and sustainable alternatives to enhance growth, improve feed efficiency, and control infectious diseases in poultry. Moreover, meeting the increasing global demand for poultry production requires the development of generally accepted and sustainable feed additives that positively impact overall poultry performance and health, while enhancing farmers’ incomes (Reuben et al., 2021). Numerous compounds, products, and biological agents have been extensively investigated in vitro and in vivo, and are commercially available in some cases. Among the antibiotic alternatives evaluated and utilized in poultry, prebiotics, probiotics, enzymes, antimicrobial peptides (AMP), organic acids, bacteriophages, synbiotics, metal, clay, hyperimmune egg yolk IgY, phytogenics, and more recently, postbiotics, have shown promisising results (Zamani et al., 2017; Humam et al., 2018). Although many of these antibiotic alternatives have garnered increased attention over the years, prebiotics, probiotics, and lately postbiotics have been the primary focus of extensive global research. Therefore, this study will investigate the impact of postbiotics on growth, meat quality, blood biochemistry, intestinal microbiota composition, and growth hormone gene expression in poultry.

USING POSTBIOTICS INSTEAD OF PROBIOTICS

The paramount concerns for a profitable venture in the poultry industry revolve around production performance, animal well-being, and welfare. The rise in inflammation incidence, heat stress, dysbiosis, and genetic selection has contributed to low-grade inflammation, leading to the development of diseases and pathogenic infections. An effective strategy to address these detrimental effects involves enhancing gastrointestinal health, particularly through immunomodulation of gut microbiota, mucin dynamics, and fortification of the intestinal barrier (Chang et al., 2022). Gut homeostasis plays a crucial role in maintaining the health of both humans and animals (Lallès et al., 2016), and emerging evidence suggests that gut microbiota significantly influences this balance (Fan & Pedersen, 2021). Though complex, the modulation of interactions between gut microbes and host health holds promise in various areas, including growth (Wang et al., 2020), aging (Wilmanski et al., 2020), fertility (Qi et al., 2019), and disease (Zmora et al., 2019). Probiotics are live microorganisms that confer health benefits to the host when administered in sufficient quantities (FAO/WHO, 2001), and have been widely accepted for their positive effects. Notably, specific strains from Lactobacillus (Zheng et al., 2020), Bifidobacterium (Picard et al., 2005), and Akkermansia (Xu et al., 2020) have demonstrated their potential in benefiting the host. However, it is worth noting that the term “probiotics” strictly pertains to live microorganisms, and the impact of dead and injured microorganisms in probiotic products has received little attention (Fiore et al., 2020). Recent research has also highlighted the beneficial effects of components and end-products derived from non-viable microorganisms, such as bacterial lysates (Esposito et al., 2018), lactic acid (Pessione, 2012), short-chain fatty acids (SCFAs) (Nagpal et al., 2018), and bioactive peptides (Zielińska & Kolożyn-Krajewska, 2018). Moreover, the safety and complex interactions of gut microbiota concerning the use of live probiotics remain subjects of investigation (Nayfach et al., 2019; Žuntar et al., 2020). In light of these challenges, postbiotics have emerged as an inspiring alternative for gut health modulation. Several terms have been used to describe postbiotics, such as ‘Tyndallized probiotics’ (Piqué et al., 2019), ‘Heat-killed probiotics’ (Li et al., 2009), ‘Paraprobiotics’ (Taverniti & Guglielmetti, 2011), and ‘Bacterial lysates’ (Jurkiewicz & Zielnik-Jurkiewicz, 2018). While the literature on postbiotics is steadily growing (Wegh et al., 2019), there is still ongoing discussion about their precise definition (Żółkiewicz et al., 2020). Initially coined by Tsilingiri et al. (2012), the term “postbiotics” refers to metabolic products derived from probiotics that exert beneficial effects on the host either directly or indirectly (Tsilingiri & Rescigno, 2013; Tsilingiri et al., 2012). In 2019, the International Scientific Association of Probiotics and Prebiotics (ISAPP) proposed the definition of ‘postbiotic’ as “preparation of inanimate microorganisms and/or their components that confers a health benefit on the host” (Swanson et al., 2020). Notably, postbiotics do not carry the risks associated with live microorganisms (probiotics), such as genetic instability, infectivity, or in situ toxin production (Guo et al., 2020). Nevertheless, the potential release of specific toxic metabolites or substrates from dead bacteria requires further assessment. In probiotic products, the proportion of live microorganisms at the end of their shelf life is uncertain due to microbial death under different storage conditions (Fenster et al., 2019). To account for this, probiotics are commonly over-dosed during production to compensate for potential losses (Sreeja & Prajapati, 2013). Conversely, the potential benefits of dead microorganisms in probiotic products have often been overlooked. Postbiotics offer the advantage of maintaining stability during industrial processes and long-term storage, making them a more feasible and practical option compared to probiotics (Wegh et al., 2019). Furthermore, postbiotics allow for precise control of the quantity of products during processing. Various microbe strains generate a variety of soluble substances, such as B vitamins, cell-surface proteins, peptides, lactic and acetic acids, plasmalogens, endo- and exo-polysaccharides, ethanol, polyphosphates, teichoic acids, diacetyl, lactocepins, and hydrogen peroxide (Rad et al., 2020). A variety of bacterial cultures have been used as paraprobiotics, with Lactobacilli and Bifidobacterium being the most often used ones. Their effectiveness once inactivated, primarily by heat, has been demonstrated. It has been discovered that various Lactobacilli species, including Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus casei, Lactobacillus fermentum, Lactobacillus rham-nosus, Lactobacillus reuteri, and Lactobacillus john-sonii, have highly effective postbiotics in the form of cell wall and cytoplasmic components. Furthermore, postbiotic qualities are recognized for Faecalibacterium prausnitzii (Iweala et al., 2019), Bacillus coagulans (Abbas et al., 2018), and Bifidobacterium species (Radhamanalan and Dharumadurai, 2023). It has been determined that L. plantarum strains, either separately or in combination, are the most common producers of postbiotics (Reuben et al., 2021). Additionally, by means of anaerobic fermentation in a specific medium and liquid drying afterwards, Saccharomyces cerevisiae is employed to produce postbiotics (Chan et al., 2022). Some advantages and functions of postbiotics utilization in poultry are shown in Figure 1.

Figure 1
Advantages and functions of postbiotics utilization in poultry.

POSTBIOTICS’ COMPONENTS

The residual presence of various microbial-derived components and molecules in postbiotics persists even after processing, which plays a pivotal role in promoting host health through diverse mechanisms. To elucidate the advantageous effects and underlying mechanisms of these postbiotic components, rigorous purification procedures have been employed, followed by their administration in both in vivo and in vitro experimental setups. Previous studies have identified potential probiotic components present in postbiotics, such as exopolysaccharides, wall polysaccharides, teichoic acids (including wall teichoic acids and lipoteichoic acids), surface layer proteins, and bacterial DNA and metabolites (Zhong et al., 2022).

EFFECTS OF POSTBIOTICS ON GROWTH PERFORMANCE

The utilization of postbiotics in broiler chicken nutrition has received attention due to their profound impact on growth rate. Postbiotics possess both bactericidal and bacteriostatic properties, effectively mitigating the proliferation of detrimental gut bacteria. Notably, postbiotics derived from L. plantarum have demonstrated inhibitory effects against various pathogens, as shown by the studies of Kareem et al. (2014), Choe et al. (2013), and Van Thu et al. (2011). Humam et al. (2019) reported a significant enhancement in growth performance, specifically in terms of final body weight (FBW) and feed conversion ratio (FCR), among broiler chickens fed postbiotics compared to the negative control group. Previous research by Kareem et al. (2016) indicated that combining inulin with postbiotics resulted in superior growth performance. This improvement can be attributed to the reduction in harmful intestinal microbes achieved through the action of postbiotics. Noteworthy findings by Thanh et al. (2009) showcased that broilers receiving a blend of postbiotics obtained from L. plantarum exhibited higher final body weight and weight gain. Similarly, Mookiah et al. (2014) reported improved growth performance in broilers fed with a combination of Lactobacillus spp. culture and prebiotic. Furthermore, Kalavathy et al. (2003) found that a mixture of 12 Lactobacillus strains positively impacted growth performance in broiler chickens. Under heat stress conditions, dietary supplementation containing Lactobacillus strains led to notable improvements in average daily gain and feed intake, as demonstrated in the study by Jahromi et al. (2017). Moreover, Zulkifli et al. (2000) observed significant enhancements in body weight, weight gain, feed intake, and feed conversion ratio of broilers under heat stress fed Lactobacillus strains compared to those fed oxytetracycline. Postbiotics operate similarly to probiotics in promoting broiler growth performance, potentially through the upregulation of nutrient transporter gene expression such as Na+-dependent glucose (SGLNC), galactose transporter (SGLRI11), and long-chain acyl CoA dehydrogenase genes, as shown by Jahromi et al. (2016). Kalavathy et al. (2003) indicated that increased nutrient utilization resulting from upregulated gene expression contributes to improved body weight in broilers. While Rahimi & Khaksefidi (2006) reported no significant differences between antibiotic and probiotic groups in broiler growth performance under heat stress, limited information is available regarding the effects of postbiotics on heat-stressed broilers. However, a current study found that administering postbiotics to heat-stressed broilers effectively promoted weight gain and feed conversion efficiency, which relates to the beneficial effects of probiotics found in heat-stressed broilers, as reported by Sohail et al. (2012). Within the postbiotic groups, Humam et al. (2019) observed higher FCR values in birds treated with RI11, RS5, and UL4 postbiotics. Particularly, the RI11 group exhibited the highest FCR value among the postbiotic groups. The inclusion of various postbiotics or their combination with inulin has consistently enhanced feed efficiency in broiler chickens, as demonstrated in studies by Thanh et al. (2009), Kareem et al. (2016), and Loh et al. (2010). Postbiotic treatment of broiler chickens has shown improvement in weight gain and FCR, while concurrently mitigating the effects of exposure to pathogenic E. coli (078), according to Abd El Ghany et al. (2022). Additionally, Thanh et al. (2009) noted that broilers fed combinations of metabolites produced by L. plantarum exhibited higher final body weight and weight gain compared to those fed negative control diets. Furthermore, the application of postbiotics from L. plantarum in heat-stressed broiler chickens resulted in elevated weight gain and superior feed conversion efficiency due to increased hepatic insulin-like growth factor 1 mRNA expression level, as observed by Humam et al. (2019). Likewise, the combined mixture of postbiotic and prebiotic in the diet of broiler chickens has been shown to improve total body weight and feed efficiency, accompanied by increased liver insulin-like growth factor 1 and growth hormone receptor mRNA expressions, according to the study by Kareem et al. (2016). In the context of C. perfringens-challenged broiler chickens, the postbiotic treatment led to improved weight gain compared to the non-treated control group, as shown in the study by Johnson et al. (2019). Conversely, Rosyidah et al. (2011) found no significant differences in body weight or weight gain in chickens fed metabolites or a combination of metabolites and acidifiers when compared to those fed positive and negative control diets.

According to Kudupoje et al. (2022), preparations based on yeast cell walls have demonstrated effectiveness against toxins derived from Aspergillus, but their effect against type-B trichothecenes is less pronounced. They looked into how well yeast cell wall extract (YCWE) and a post-biotic yeast cell wall-based mix (PYCW), both applied at a rate of 0.2% of the feed, remedied aflatoxins in broiler chickens that had been exposed to zearalenone, deoxynivalenol, and T-2 toxin (T2). PYCW and, to a lesser extent, YCWE have been included as a potential defenses against toxines. PYCW responded more strongly to NDV and IBV immunization, improved growth performance, and enhanced liver function. In addition, the European Poultry Production Efficiency Factor was higher in the YCWE- and PYCW-supplemented treatments than in the control group. The study revealed that YCWE complemented with PYCW could improve the remediation of the negative effects from a multi-mycotoxin dietary challenge in broiler birds. The effects of feeding broiler chicks a postbiotic produced from Bacillus subtilis ACCC 11025 were investigated by Fang et al. (2024). The dietary interventions consisted of a base diet supplemented with postbiotics at 0.000%, 0.015%, 0.030%, or 0.045%. By improving feed efficiency and modifying the composition of bacterial communities in excreta - that is, by reducing the abundance of Salmonella in excreta and increasing the presence of Lactobacillus bacteria -, the results showed that supplementing broiler chick diets with 0.015% postbiotic was an effective way to increase body weight gain and meat yield. The effects of a proprietary saponin-based feed additive (0.25 kg/MT) and a well-known postbiotic feed additive (Original XPC, Diamond V-a Saccharomyces cerevisiae fermentation product) on turkey performance were studied by Chaney et al. (2023). At 12 and 15 weeks of age, they noticed notable variations in body weight, whereby the postbiotic plus saponin therapy group produced heavier chicks at both timepoints. When comparing the postbiotic group with the control group, there were notable variations in FCR between the ages of 0 and 18 weeks. There were no discernible variations in terms of livability or feed intake. The study’s findings indicate that a postbiotic and saponin combination may have cumulative effects on turkey growth. Postbiotics are thought to be helpful because of their antibacterial qualities, which work similarly to antibiotics to inhibit pathogenic bacteria in the gastrointestinal system, while boosting growth (Soren et al., 2023). When fermented Saccharomyces cerevisiae at 0.1%, 0.3%, or 0.5% were added to diets, Zeinali & Mohammadi (2022) found that the feed conversion ratio and daily weight growth were considerably higher than in the control groups (p). Birds fed the fermented product of this same microorganism at 0.25% and 0.50% had significantly improved average daily gain compared to those fed only a basal diet (p=0.04), according to a study by Gao et al. (2009). Chaney et al. (2023) also observed similar results. Additionally, Saccharomyces cerevisiae fermented product supplementation also increased growth and feed utilization (Chuang et al., 2021; Linh et al., 2021; Ismael et al., 2022; Liza et al., 2022), but it had no influence on livability or feed intake in any of these experiments. Although Saccharomyces cerevisiae fermented product (SCFP) has the potential to promote growth, its effectiveness in this regard has not been convincingly established by several investigations. While Cortés-Coronado et al. (2017) observed no changes in final body weight, average daily gain, feed intake, feed conversion ratio, or liveability even when different amounts of SCFP were tested, Lensing et al. (2012) and Nelson et al. (2018) found no significant differences in body weight or feed conversion ratio following SCFP supplementation. Further research has confirmed this, using several different concentrations of SCFP, including 0.1% (Chuang et al. 2021), 0.1255%, 0.125%, and 0.25% (Firman et al. 2013); 250 and 500 mg/kg (Lin et al., 2023); and 0.625, 1.250, and 2.500 kg/ton (Oliveira et al., 2022).

EFFECTS OF POSTBIOTICS ON LIVABILITY

The incorporation of postbiotics in broiler diets demonstrated a notable trend of reduced mortality compared to other treatments, as evidenced in the study by Humam et al. (2019). Soomro et al. (2019) reported that feed restriction for 4-8 hours resulted in efficient feed utilization, with the highest weight gain observed in groups B2 (92.3 g/bird) and C2 (91.9 g/bird). Protexin supplementation paired with feed restriction led to an improved feed conversion ratio (FCR) and reduced mortality. Furthermore, the lower mortality observed in the protexin-treated groups may be attributed to the potential role of protexin in suppressing undesirable microorganisms, thereby enhancing the resistance and overall performance of broiler chickens (Anjum et al., 2005). In a study conducted by Abu-Akkada & Awad (2015), supplementing a probiotic preparation (Lacto G®) to broilers exhibited promising results in preventing mortality, reducing oocyst output, and mitigating the severity of E.tenella lesions. Although probiotics have been associated with potential benefits in reducing mortality from enteric pathogens through competitive exclusion, inconsistent effects on mortality were observed in trials involving Lactobacillus preparations with broilers (Watkins & Kratzer, 1984; Jin et al., 1998; Jin et al., 2000; Zulkifli et al., 2000). However, challenge experiments involving pathogens like Escherichia coli, Salmonella typhimurium, and Staphylococcus aureus demonstrated a probiotic-induced reduction in mortality (Watkins & Miller, 1983; Edens et al., 1997). Notably, the addition of probiotics to drinking water led to a significant decrease in mortality in controlled trials, accompanied by a 4.87% increase in total final body weight (Timmerman et al., 2006). Probiotic supplementation exerts beneficial effects on gut health and performance by diminishing the population of pathogens in the gastrointestinal tract through competitive exclusion or the production of antimicrobial peptides. This, in turn, improves intestinal maturation and integrity, and modifies immune responses, as highlighted in studies by Lan et al. (2005) and Sadeq et al. (2015). Pelicano et al. (2005) also observed a reduction in mortality percentage with symbiotic supplementation in broilers. Emami et al. (2021) conducted research demonstrating that during a subclinical, naturally occurring necrotic enteritis, specific probiotic supplementation proved effective in reducing intestinal lesions and mortality, while enhancing performance. This effect was potentially attributed to the development of a signature microbial profile in the intestinal mucosal layer.

EFFECT OF POSTBIOTICS ON CARCASS TRAITS

In the poultry industry, a primary concern revolves around achieving higher yield percentages of saleable products and enhancing edible portions. Feed additives are commonly employed to boost the metabolism rate, thereby increasing the size of internal organs and carcasses (Abdel-Hafeez et al., 2017). Research has explored the impact of postbiotics on carcass traits. Humam et al. (2019) found that dietary supplementation with various postbiotics did not affect carcass yield in broiler chickens under heat stress. Similarly, Kareem et al. (2015) observed that the combination of postbiotics and inulin did not influence carcass yield in broilers. Furthermore, antibiotic and probiotic supplementation did not affect carcass yield in broiler chickens (Shimokomaki, 2012). Studies focusing on probiotics have revealed their potential to modulate intestinal microbiota, reduce pathogens, enhance immunity, and improve the sensory and microbiological properties of broiler meat (Pelicano et al., 2005; Kabir, 2009). Probiotic supplementation has been shown to significantly impact carcass yield, live weight gain, immune response, and the composition of prominent meat cuts (Soomro et al., 2019). However, conflicting results have been reported in some studies. Abdel-Raheem & Abd-Allah (2011) and Pelicano et al. (2003) reported no significant effect of different probiotics on the carcass yield and various organ weights of broiler chickens at 42 days of age. Similarly, de Souza et al. (2018) and Cengiz et al. (2015) found that dietary supplementation with probiotics during environmental challenges did not influence the yields of carcass, breast, leg, and wings. In Japanese quail, the addition of probiotics and prebiotics to the diet decreased liver and heart weights (Nikpiran et al., 2013). Midilli et al. (2008) did not observe any significant impact of probiotics and Mannan-oligosaccharides on carcass yield. Mahmud et al. (2008) reported that the highest abdominal fat percentage was recorded in birds fed the control diet, while the lowest value was recorded in birds fed the MOS-supplemented diet. The specific mechanisms responsible for the reduction of lipid synthesis by prebiotics and probiotics have not been fully elucidated, but they may involve the stimulation of beneficial bacteria, such as Lactobacillus, which can decrease the activity of acetyl-CoA carboxylase, a rate-limiting enzyme in fatty acid synthesis (Abdel-Hafeez et al., 2017). Regarding symbiotics, Saiyed et al. (2015) found no significant effect on carcass, breast, and thigh weight; while Toghyani et al. (2011) and Shabani et al. (2012) reported no impact on various organ weights. Conversely, Abdel-Raheem and Abd-Allah (2011) and Saiyed et al. (2015) observed an improvement in carcass traits, with an increase in dressing percentage due to symbiotic supplementation. Prebiotics, when added to the broiler diet, have been shown to improve carcass characteristics, likely by inhibiting the colonization of intestinal pathogens and enhancing nutrient utilization (Toghyani et al., 2011). Santin et al. (2001) demonstrated increased yields in the breast, gizzard, and thighs through the use of symbiotics and MOS. Furthermore, probiotic microorganisms have been observed to enhance protein availability and nutrient uptake, leading to improved nitrogen stability and, consequently, enhanced carcass quality (Falaki et al., 2011). Many investigations have been carried out to evaluate the effect of postbiotics on carcass attributes. It is yet unknown what are the precise mechanisms underlying the majority of researches’ conclusion that postbiotics have no influence on carcass features (Soren et al., 2023). The addition of 0.625, 1.250, and 2.500 kg/ton of postbiotic generated from Saccharomyces cerevisiae to broiler diets did not significantly affect carcass yield or breast yields, according to a study by Oliveira et al. (2022) (p>0.05). According to Zeinali & Mohammadi (2022), adding 0.1%, 0.3%, or 0.5% of fermented Saccharomyces cerevisiae to broiler diets did not significantly affect carcass characteristics, or thigh, breast, or wing weight (p>0.05).

EFFECTS OF POSTBIOTICS ON MEAT QUALITY

The impact of postbiotics on meat quality and carcass traits has been a subject of considerable study. Danladi et al. (2022) found that both postbiotics and paraprobiotics had no significant difference in their effects on the carcass yield of broiler chickens, but they did show a significant effect on abdominal fat and intestines. The postbiotic and paraprobiotic groups exhibited a decrease in abdominal fat compared to the negative and positive control groups, with the paraprobiotic RG14 showing the lowest abdominal fat. This finding is consistent with Loh (2017), who found postbiotic metabolites to show potential usefulness in addressing high meat and egg yolk cholesterol issues. Additionally, L. plantarum bacteria were reported to cause a reduction in fat deposits in chickens (Ho et al., 2000). Humam et al. (2019) also reported that feeding postbiotics to broiler chickens under heat stress did not affect their carcass yield, and similar results were observed when a combination of postbiotics and inulin was fed to broiler chickens (Kareem et al., 2015). Similarly, antibiotic and probiotic supplementation did not affect the carcass yield in broiler chickens (Shimokomakillal, 2012). In other studies, dietary supplementation with different probiotics had no significant effect on the carcass yield and various meat cuts in broiler chickens (Pelicano et al., 2003; Abdel-Raheem & Abd-Allah, 2011; Cengiz et al., 2015; de Souza et al., 2018). Aside from the health implications, the quality of meat obtained from chicken muscle is crucial for the economics of meat processing industries. The water-holding capacity (WHC) of meat, indicated by drip and cooking losses, determines the profit in meat sales (Den Hertog-Meischke et al., 1997). Both acute and chronic heat stress exposure can negatively affect meat quality (Sandercock et al., 2001; Liu et al., 2018). Acute heat stress alters aerobic metabolism, glycolysis, and intramuscular fat deposition, leading to pale meat color, reduced WHC, and higher shear force (Wang et al., 2017; Zhang et al., 2012). Additionally, acute heat stress affects blood acid-base status and muscle membrane integrity (Zaboli et al., 2019). Humam et al. (2020) conducted a study on heat-stressed broilers fed with postbiotics and found that the birds supplemented with postbiotics had significantly lower drip loss and cooking loss compared to the negative control, and oxytetracycline-, and ascorbic acid-fed groups. Similar findings were reported in broilers fed combinations of postbiotics and inulin under normal ambient temperature (Kareem et al., 2016). Dietary probiotics also resulted in significant reductions in drip loss in the breast muscle of chickens (Zhou et al., 2010). Moreover, Humam et al. (2020) reported that shearing force was lower in the birds fed with various postbiotics compared to the antibiotic and negative control groups, indicating that postbiotics can counteract the effects of thermal stress on broilers by influencing antioxidant enzyme activities. Similar results were observed in birds fed with probiotics (Zhou et al., 2010). A study on probiotic supplementation revealed that meat pH, color, drip loss, cooking loss, and tenderness were improved due to the up-regulation of protein-related substrate metabolism, antioxidant, and immune systems, leading to alterations in various metabolic pathways (Zheng et al., 2014). Similarly, the inclusion of postbiotics in broiler diets under heat stress is expected to deliver similar positive effects on meat quality, as observed in probiotic-fed broilers (Humam et al., 2020). Another indicator of meat quality is its pH, which is considered good for broiler breast meat when around 6.0 (Alvarado et al., 2007). Humam et al. (2020) reported that the breast meat pH of all treatment groups ranged from 5.7 to 6.0, indicating good quality. The birds fed with postbiotics (RI11, RS5, UL4) showed higher pH compared to the positive and negative control groups, further highlighting the role of postbiotics in maintaining meat quality. Zaboli et al. (2019) reviewed three main pathways through which postbiotics exert their action in improving meat quality in broiler chickens under heat stress. Firstly, they prevent a rapid drop in pH, which can be detrimental to meat quality. Low pH has been associated with low redness, high drip, and cooking losses in chicken breast meat (Hao & Gu, 2014; Feng et al., 2008). Secondly, postbiotics enhance the antioxidant activities of glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase (CAT), which helps to alleviate the effects of heat stress on meat quality by reducing oxidative damage. The third likely mechanism involves lowering corticoid hormone levels, specifically the secretion of corticosterone. Corticosterone has been shown to accelerate reactive oxygen species (ROS) production, which may result in pale colors and high drip loss in broiler meat (Sato et al., 2010).

EFFECT OF POSTBIOTICS ON GUT HEALTH

Intestinal epithelial cells, the microbial community, and the immune system constitute the essential components of the gut ecosystem (Fathima et al., 2022). In the past, before large-scale incubation of eggs in incubators, the eggs remained in contact with the nest or the hen during incubation, facilitating the vertical transmission of the maternal microbiota to chicks (Lavelle et al., 2010). However, in modern commercial hatcheries, chicks are hatched in a sanitized environment with no contact with the hen, resulting in their gut microbiota being solely dependent on environmental sources, leading to a decrease in microbial diversity (Maki et al., 2020). As a potential solution, transferring the gut microbiota of healthy adult chickens to day-old chicks is being considered as a future approach to control foodborne pathogens in poultry (Fathima et al., 2022). Microorganisms colonize various regions of the chicken’s gastrointestinal tract, including the gut mucosal epithelium, gut lumen, and caeca (Donaldson et al., 2017). Factors such as the age of the bird, region of the gastrointestinal tract, bird genotype, housing conditions, and feed composition influence microbial composition and diversity (Ding et al., 2017). In the past, conventional microbiological methods limited the research and identification of individual components of the chicken gut microbiota. However, the advent of 16S rRNA-based next-generation sequencing tools has revolutionized the characterization of chicken gut microbiota (Ngunjiri et al., 2019). The use of antibiotics can disrupt the delicate balance of gut microbiota, leading to a decrease in species diversity and an overgrowth of harmful bacteria like toxigenic C. difficile (Ianiro et al., 2020). Antibiotics can also compromise the integrity of the intestinal epithelium, making it more susceptible to damage, and facilitating the invasion of enteric pathogens (Willing et al., 2011). Gut microbiota dysbiosis, often caused by infections with enteric pathogens like C. perfringens, is associated with perturbation of gut immune homeostasis and intestinal inflammation (Lacey et al., 2018). While probiotics, prebiotics, and synbiotics have shown promise in ameliorating C. perfringens-induced inflammatory responses and restoring gut homeostasis, there are emerging concerns about potential virulence factors, antimicrobial resistance, and other side effects associated with probiotic supplementation (Wassenaar and Klein, 2008; Al-Baadani et al., 2018; Kothari, Patel, & Kim, 2019). To address these concerns, postbiotics have emerged as safer alternatives to antibiotics and live probiotics in poultry production (Tsilingiri & Rescigno, 2013; Haileselassie et al., 2016). Postbiotics, such as cell-free supernatants obtained from specific strains of L. plantarum, have been shown to inhibit potential pathogens and contribute to maintaining gut health (Kareem et al., 2014). The antimicrobial properties of postbiotics are primarily attributed to bacteriocins and short-chain fatty acids (SCFAs) (Aguilar-Toalá et al., 2018). Unlike live microbial strains used as probiotics, postbiotics can enhance endogenous beneficial microorganisms within the host’s gut (Iweala & Nagler, 2019; Homayouni Rad et al., 2020). Research on the beneficial effects of postbiotics in poultry and other animals has revealed their potential as safe and effective feed additives (Mantziari et al., 2020). The metabolites in postbiotics, such as lactic acids, bacteriocins and SCFAs, play significant roles in protecting against pathogen invasion and promoting gut health (Jacobson et al., 2018; Antunes et al., 2019; Lamas et al., 2019; Schulthess et al., 2019). Additionally, postbiotics may modulate gut microbiota through quorum sensing and adhesion, further contributing to their beneficial effects (Fuqua et al., 1994; LaSarre & Federle, 2013; Monteagudo-Mera et al., 2019). Avian colibacillosis poses significant challenges in the poultry industry, with antibiotic resistance being a major concern (Ebrahimi-Nik et al., 2018; Roth et al., 2019). Biotic feed additives, including postbiotics, have shown promise as viable alternatives to protect poultry health and production levels (Klemashevich et al., 2014; Abd El Ghany et al., 2022). Studies have demonstrated the efficacy of postbiotic treatments in reducing the severity of E. coli infections, and improving gut health and growth performance in broilers and layers (Choe et al., 2012; Loh et al., 2014; Kareem et al., 2017; Humam et al., 2019; Johnson et al., 2019). The antimicrobial metabolites of postbiotics, such as organic acids and bacteriocins, contribute to their ability to decrease pathogen proliferation in the gut (Abd El Ghany et al., 2022). In conclusion, the use of postbiotics as feed additives shows great potential in enhancing the health and productivity of poultry while reducing the reliance on traditional antibiotics. Postbiotics offer a safer and more effective alternative to live probiotics, providing a means to maintain gut health and combat pathogenic infections in poultry production (Fancher et al., 2020). Further research in this area is crucial to explore and optimize the full potential of postbiotics in sustainable poultry production.

EFFECT OF POSTBIOTICS ON INTESTINAL HISTOMORPHOLOGY

The assessment of intestinal morphology provides valuable insights into nutrient absorption efficiency, with increased villus height, shorter crypt depth, and a higher villus height-crypt depth ratio indicating improved gut function and animal health (Jha et al., 2020). Villi play a pivotal role in nutrient absorption within the small intestine. Enhanced villus height and reduced crypt depth have been associated with increased nutrient absorption, reduced gastrointestinal secretion, and improved growth performance (Caspary, 1992). Fan et al. (1997) observed a positive correlation between increased villus height and VH: CD ratio, and elevated epithelial cell turnover. Previous studies have demonstrated that the supplementation of postbiotics can enhance intestinal morphology in broilers, resulting in increased villus height in the duodenum and ileum (Kareem et al., 2016). Similarly, Humam et al. (2019) revealed that broilers fed diets containing antibiotics, ascorbic acid, and various postbiotics exhibited increased villus heights and VH: CD ratios in the duodenum, jejunum, and ileum, with postbiotic RI11 showing the most significant effect. These findings align with previous studies that have shown positive effects of postbiotics on mucosal architecture, villus height, and improved growth performance in broiler chickens (Thanh et al., 2009; Kareem et al., 2016). Based on the current findings, postbiotics exert their effects by improving intestinal morphology and increasing the populations of beneficial bacteria, such as lactic acid bacteria, thus reducing the risk of villi damage caused by gut pathogens (Thanh et al., 2009; Kareem et al., 2016; Loh et al., 2010; Thu et al., 2011). Notably, Danladi et al. (2022) reported that paraprobiotic RG11 and strain RI11 (both postbiotic and paraprobiotic) contributed to more significant improvements in broiler histomorphology compared to other strains. Documented evidence indicates that postbiotics can enhance the histomorphology of the small intestines by promoting beneficial microbes such as LAB, which can mitigate the risk of villi damage caused by gut pathogens (Thu et al., 2011; Kareem et al., 2016). The dietary supplementation of probiotics, such as Bacillus subtilis, Bacillus licheniformis, and Saccharomyces cerevisiae, has been shown to increase the villus height to crypt depth ratio, indicating promotion of the absorptive surface in the duodenum and ileum of broilers (He et al., 2019). This effect is likely attributed to the beneficial bacteria in probiotics, which may enhance crypt cell proliferation in the small intestine and consequently increase the growth rate in broilers (Ahmad, 2006). Additionally, Bacillus licheniformis in probiotics can colonize and create niches in the small intestine, providing positive protection for villi against pathogens and promoting their growth (Deng et al., 2012). However, Sohail et al. (2012) reported that probiotics had no effect on stress-induced injury in the intestinal morphology of 42-day-old chickens, possibly due to variations in the types and amounts of probiotics used in different studies. Furthermore, the improvement of intestinal morphology and the integrity of the intestinal barrier are essential for epithelial cell function, which may contribute to the improved Apparent Total Tract Digestibility (ATTD) of nutrients (Narasimha et al., 2013). The functionality of the intestinal barrier and nutrient absorption can be directly impacted by mucosal epithelium damage, and probiotics have been found to regulate intestinal immunity and the mRNA expression of tight junction proteins in broilers (Gadde et al., 2017). The addition of probiotics to diets can promote the gene expression of ZO-1 in the jejunal mucosa of broilers, thus enhancing jejunal mucosal barrier function and reducing the feed weight gain ratio and intestinal coliform count, while also increasing the duodenal villus height to crypt depth ratio. These results suggest that a mixture of probiotics in the diet can effectively improve specific aspects of the intestinal barrier function (He et al., 2019). Probiotics have shown adherence to the intestinal epithelium, resistance to acidic conditions, and the ability to antagonize and competitively eliminate certain pathogens in vivo (Zulkifli et al., 2000). Bacillus licheniformis and Bacillus subtilis, as aerobic bacteria, create an anaerobic environment in the intestine, facilitating the colonization of anaerobic bacteria such as Lactobacilli and Bifidobacteria. These lactic acid-producing bacteria create a more acidic environment, which hinders the growth of opportunistic pathogens (Rodríguez-Cabezas et al., 2010). de Souza et al. (2024) studied broiler hens fed 1 mL of a Lactobacillus spp. mixture (including probiotic, paraprobiotic, and postbiotic mixture) orally via gavage, which provided approximately 2.2 × 109 CFU/mL. The combination mitigated most of the intestinal damage caused by the Clostridium perfringens and Deoxynivalenol challenges, with a partially protective effect. The antioxidant defense against oxidative stress caused by Clostridium perfringens was not strengthened by the Lactobacillus species treatments. Maintaining a healthy digestive system in broilers is imperative for optimal growth performance and good health, as it greatly facilitates nutrient absorption due to its increased surface area. Studies have shown that higher nutrient absorption rates in chickens are linked to a longer villus length, a shallower crypt depth, and an increased villus to crypt depth ratio (Rezaei et al., 2014). This ratio has been definitively proven to be beneficial in terms of nutrient uptake. Hence, improving this ratio can lead to improved nutrient absorption (Johnson et al., 2019; Jha et al., 2020). Ismael et al. (2022) and Sadeq et al. (2015) both conducted studies with the integration of Saccharomyces cerevisiae fermented product (SCFP) at 0.625 kg/ton and Saccharomyces cerevisiae cell wall extract at 200, 400, and 800 mg/kg in broiler chicken diets, respectively. This resulted in significant differences seen in villi length, crypt depth, and villi length to crypt depth ratio when compared to the control group. Lin et al. (2023) studied supplementation with 250mg and 500mg/kg of SCFP, which resulted in decreased crypt depth together with increased villus height, and a higher villus crypt ratio compared to the control group (p<0.05). Additionally, Chuang et al. (2019) found that administering 0.1% SCFP significantly raised villus height as well as the villus-crypt ratio (p<0.0001); however, there was a lessened crypt depth (p=0.0002). In contrast to the above observations, Chuang et al. (2021) demonstrated that the postbiotics developed by the co-fermentation of Saccharomyces cerevisiae and phytase using wheat bran as a substrate at doses 5% and 10% led to a significantly greater villus height (p<0.05); on the other hand, no significant difference was observed regarding crypt depth and the villus height to crypt depth ratio between all groups included in the study. Firman et al. (2013) reported that Saccharomyces cerevisiae fermentation product (SCFP) at 0.0625, 0.125, and 0.25% caused no statistical differences in villi height, or crypt depth.

EFFECTS OF POSTBIOTICS ON CAECUM MICROBIAL POPULATION AND PH

The gut microbiota plays a crucial role in maintaining gastrointestinal health (Gareau et al., 2010). However, environmental stressors disrupt the stability of the intestinal microbial ecosystem, leading to dysbiosis (Suzuki et al., 1983). Postbiotics, which are metabolic products derived from probiotic bacteria, have been found to have a beneficial impact on preserving healthy intestinal microbiota (Kareem et al., 2016). In a study conducted by Humam et al. (2019) on heat-stressed broiler chickens, various postbiotics produced from Lactobacillus plantarum were evaluated for their effects on caecal microbiota. The results demonstrated a significant reduction in the abundance of Enterobacteriaceae in broilers supplemented with postbiotics, compared to the negative control (NC) and antibiotic groups. Moreover, broilers fed with postbiotics exhibited a notable increase in protective bacteria and the overall caecal bacterial count, in contrast with the NC group. A noteworthy finding was the strong negative correlation between beneficial bacteria (Lactobacillus and Bifidobacterium) and caecal pH. Similarly, a negative correlation was observed between beneficial bacteria and potentially harmful bacteria like Enterobacteriaceae, E. coli, and Salmonella. These correlations provide valuable insights into the relationship between gut microbiota, caecal pH, and the inhibitory effects of beneficial bacteria against pathogens by lowering caecal pH. Kareem et al. (2016) also investigated the effects of different combinations of a basal diet, inulin, and a postbiotic (RG14) on caecal bacteria in broilers. Their study showed that broilers receiving the combination had significantly higher counts of total bacteria and Bifidobacteria compared to those receiving basal diets and antibiotics. Similar outcomes have been reported in previous research, where the inclusion of L. plantarum-derived metabolites in broiler and layer feeds resulted in increased populations of lactic acid bacteria (Thanh et al., 2009; Choe et al., 2012). This phenomenon can be attributed to the postbiotics’ ability to promote the growth of protective bacteria (Lactobacillus and Bifidobacterium), while suppressing the proliferation of pathogenic bacteria in the gut epithelium (Loh et al., 2013). The effect is further intensified by the reduction of intestinal and fecal pH induced by L. plantarum metabolites (Aguilar-Toalá et al., 2018), which contain bacteriocins, short-chain fatty acids (SCFAs), and organic acids that contribute to the reduction of gut pH (Thanh et al., 2009; Thu et al., 2011). This acidic environment hinders the growth of acid-intolerant bacterial species such as E. coli and Salmonella, and disrupts the physiology of these bacteria by penetrating their cells with non-ionized organic acids (Wang et al., 2016). The advantageous effects of beneficial bacteria such as Lactobacilli and Bifidobacterium are multifaceted, encompassing competitive exclusion, prevention of pathogen-host epithelial cell contact, and elicitation of immune responses (Steer et al., 2000; Gil De Los Santos et al., 2005; Liu et al., 2014). Humam et al. (2019) demonstrated that postbiotics were especially effective in enhancing gut microbiota, even under heat-stress conditions. In the absence of postbiotic supplementation, heat-stressed broilers experienced increased colonization by pathogenic bacteria like Salmonella and E. coli, consistent with earlier findings on heat stress and intestinal pathogen colonization (Jahromi et al., 2017; Pearce et al., 2013). The combination of postbiotics and inulin led to a notable increase in total bacterial and beneficial bacterial populations, along with a decrease in pathogenic bacteria in the cecal digesta of broiler chickens. This outcome is attributed to the increased production of acetic acid, which modulates gut microbiota by lowering gut pH (Kareem et al., 2017). Similarly, Kim et al. (2011) observed that feeding broilers with FOS and MOS increased the diversity and populations of total bacteria and Lactobacilli while reducing E. coli and C. perfringens in the ileum. Moreover, Chen et al. (2015) confirmed that palm kernel expeller (PKE) extract containing monosaccharides (including mannose) and oligosaccharides (mainly mannobiose) could effectively modulate gut microbiota, particularly by reducing E. coli populations in rats. Additionally, Choe et al. (2012) reported that liquid metabolite combinations derived from three L. plantarum strains increased the population of fecal lactic acid bacteria, and reduced fecal pH and Enterobacteria in laying hens. However, the influence of xylo-oligosaccharides supplementation on cecal microbiota, lactic acid bacteria, Bifidobacterium, E. coli, or Salmonella in broiler chickens was not observed in a study by Suo et al. (2015). Likewise, the supplementation of oligosaccharides extract from palm kernel expeller (OligoPKE) did significantly alter the microbiota of the cecal digesta in broiler chickens, as reported by Rezaei et al. (2015). The impact of a postbiotic derived from Lactobacillus helveticus ATCC 15009 on mitigating experimental Salmonella Gallinarum infection in commercial layer chicks was found by Ribeiro et al. (2023). When postbiotic was added at 5cfu to challenged chicks, it was discovered that the prophylactic therapy had changed the intestinal microbiota and decreased the amount of S. gallinarum in the chicks’ liver and cecum (p<0.05). These novel alternatives could aid the chicken industry in producing safer food for human consumption by preventing S. gallinarum.

Chaney et al. (2022) undertook a study to assess a postbiotic supplement in tandem with an industry control diet and the ensuing burden of Salmonella enterica on a single commercial broiler farm in Honduras. Saccharomyces cerevisiae-derived postbiotic (SCFP) (27.8%) and control (30.6%) had similar rates of Salmonella prevalence in litter; however, the amount of Salmonella in positive samples was lower (p=0.04) for SCFP (3.81 log10 most probable number (MPN)/swab) than for control (5.53 log10 MPN/swab). Salmonella was found in the cecum less frequently (p=0.0006) in broilers fed SCFP (3.4%) as opposed to the control group (12.2%). These findings show how postbiotics can be used as a preharvest intervention to lower Salmonella enterica in broiler chickens. According to Guan et al. (2024), when broilers were challenged with Salmonella enterica serotype Enteritidis, the use of Lactiplantibacillus plantarum postbiotics (Lactiplantibacillus plantarum cell-free culture, or LPC) at a rate of 0.8% maintained the broilers’ growth performance. This was demonstrated by an increase in BW, ADG, and ADFI. Villus length and villus/crypt were increased, intestinal injury-related genes (Villin, MMP3, I-FABP) were regulated, tight junctions (ZO-1 and Claudin-1) were strengthened, and SE-induced intestinal mucosal damages were greatly prevented by LPC. Moreover, by blocking the NF-κB signaling pathway (lowered levels of TLR4, MyD88, IRAK4, and NF-κB), LPC inhibited the activation of the NLRP3 inflammasome. Through a decrease in Alistipes and Barnesiella and an increase in Ligilactobacillus, LPC regulated the gut flora. Through NLRP3 inflammasome suppression and gut microbiota optimization, LP postbiotic was found to be efficient in protecting broilers against Salmonella infection. According to several studies, Saccharomyces cerevisiae-produced postbiotics have several health benefits and can inhibit a range of gut pathogens, including Salmonella typhimurium, E. coli, and vancomycin-resistant Enterococcus. These findings imply that postbiotics could be used as an alternative to antibiotics (Soren et al., 2023). These postbiotics have a number of antibacterial ingredients, such as proteins, peptides, and organic acids, which lower the pH of the stomach to stop the growth of pathogens and promote the health of chickens (Aguilar-Toalá et al., 2018). In contrast to earlier studies by Chuang et al. (2019) and Kang et al. (2015), which found no significant differences or enhancement in Lactobacillus, Salmonella, and Escherichia coli levels with dietary supplementation of SCFP or fermented rice bran, respectively; Chuang et al. (2021) reported increased concentrations of Lactobacillus spp. in the caecum in response to postbiotics formed by Saccharomyces cerevisiae at 10%. However, in contrast to control groups, Roto et al. (2017) and Gingerich et al. (2021) observed that the addition of SCFP at 1.25 g/kg and 1.5 kg/MT significantly decreased Salmonella concentrations. These findings suggest that Saccharomyces cerevisiae, when used at specific concentrations, may have inhibitory effects on pathogenic bacteria. Chaney et al. (2023) reported on the evaluation of feed-additive technologies’ efficacy against Salmonella enterica (SE) as part of pre-harvest food safety interventions. Researchers assessed how commercial pullets exposed to Salmonella enteritidis (SE) directly and indirectly responded to the dietary addition of a Saccharomyces cerevisiae fermentation-derived postbiotic (SCFP) supplement (Diamond V, Original XPC®). In the ceca or ovary tissues of birds that were directly challenged, no statistically significant variations were seen between the groups regarding the occurrence of SE. Moreover, there was a significant difference in mean SE cecal load between the treatment group (1.69 Log10) and the control group (2.83 Log10) (p=0.005), for the indirectly exposed cohort at 7 days post-challenge (50.0%-treatment group, compared to 72.5%-control group). Approximately 10% fewer birds in the treatment group remained positive than in the control group at 14 days after the challenge, although no significant differences were found (p>0.05). According to our results, feeding pullets meals enriched with SCFP postbiotic may help pre-harvest food safety measures by reducing the risk of SE colonization in pullets shown horizontally.

EFFECTS OF POSTBIOTICS ON VOLATILE FATTY ACIDS PRODUCTION

Volatile fatty acids (VFAs), encompassing acetic, propionic, isobutyric, butyric, isovaleric, and valeric acids, are predominantly absorbed in the large intestine, serving as a vital source of energy for the host (Franklin et al., 2002). Kareem et al. (2017) conducted a study revealing that the supplementation of various levels of postbiotic and inulin combinations significantly increased the concentration of acetic acid, while the levels of butyric acid, propionic acid, and total VFAs remained unaffected. This finding aligns partially with report of Mookiah et al. (2014), which demonstrated that probiotics, prebiotics, and symbiotics elevated the concentrations of acetic acid, propionic acid, butyric acid, and total VFAs in the cecal digesta of broiler chickens compared to the control diet. Similarly, Loh et al. (2013) observed that different levels of metabolite combinations derived from L. plantarum resulted in increased acetic acid concentration when compared to the control diet in post-weaned piglets. In poultry, the ceca serve as a site of extensive strict anaerobic activities, including the formation of short-chain fatty acids, when birds are fed a diverse range of diets (Saengkerdsub et al., 2007). Microorganisms in the gastrointestinal tract of various animal species, including poultry, possess the capability to hydrolyze and ferment dietary fiber into oligosaccharides and other low molecular weight carbohydrates (Dunkley et al., 2007). In the intestines, prebiotics are fermented by beneficial bacteria, leading to the production of short-chain fatty acids (Al-Sheraji et al., 2013). Beyond their physical barrier role, lactic acid bacteria (LAB) are also involved in creating an unfavorable environment for unnecessary bacteria such as Salmonella and E. coli, as LAB can produce and secrete antimicrobial substances, including bacteriocins and VFAs, which reduce pH and inhibit the viability of Enterobacteriaceae (ENT) (Reid, 2001). The bacteriostatic effects of VFAs in the ceca (van der Wielen et al., 2000) also contribute to the reduction of ENT. The observed negative correlation between ENT and LAB reinforces the concept of competitive exclusion, where LAB outcompete ENT. In studies involving metabolite combinations produced by Lactobacillus plantarum, an increase in the number of LAB was associated with a reduction in ENT count (Loh et al., 2010).

EFFECTS OF POSTBIOTICS ON IMMUNITY AND CYTOKINE EXPRESSION

Cytokines are small extracellular signaling proteins synthesized by the host, playing pivotal roles in immunity by facilitating cellular communication during immunological development and immune response (Saleh & Al-Zghoul, 2019). Immune cells such as T lymphocytes, B lymphocytes, macrophages, and natural killer cells produce both proinflammatory and antiinflammatory cytokines (Jeurissen, 1991). T lymphocytes can be classified into two types: Th1 and Th2 cells. Th1-type cytokines, including IL-2, IL-8, IFN-gamma, and TNF-alpha, promote cellular immunity; while Th2-type cytokines, such as IL-6 and IL-10, play a role in humoral immunity (Xie et al., 2015; Kidd, 2003). These small protein molecules are released as part of the immune response when animals are exposed to infections, inflammation, or shock (Hakansson & Molin, 2011). The modulation of cytokine secretion may be associated with a decreased incidence of disease, but the precise mechanisms of immunomodulation remain elusive (Kareem et al., 2017). Commensal bacteria, when fed as isolated strains, can have diverse effects, ranging from anti-inflammatory to pro-inflammatory responses (Foligne et al., 2007). A balanced gut microbiota serves as an efficient barrier against pathogen colonization and produces metabolic substrates, such as vitamins and short-chain fatty acids, while stimulating the immune system in a non-inflammatory manner. The composition of the colonizing microbiota has been correlated with variations in immunity (O’Hara & Shanahan, 2006). Heat stress negatively impacts intestinal integrity, leading to increased permeability to endotoxins, antigens, and inflammatory cytokines (Alhenaky et al., 2017). This condition also elevates the expression of proinflammatory cytokines and suppresses anti-inflammatory cytokines in broilers (Gadde et al., 2017). Heat stress-induced gut damage prompts commensal bacteria to release endotoxins, promoting the production of proinflammatory cytokines (De Boever et al., 2008). Humam et al. (2021) demonstrated in their study that the increase in the levels of proinflammatory cytokine such as IL-8 and TNF-alpha in heat-stressed broilers could be mitigated by dietary supplementation with postbiotics. Feeding postbiotic RI11 at different levels modulated inflammatory processes by restoring cytokine balance, thereby reducing potential inflammation-induced injuries that occur after heat stress in broiler chickens. Additionally, groups treated with the postbiotic RI11 showed lower expressions of IL-8 and TNF-alpha, and higher expressions of IL-10 compared to other treatment groups. The differential expression of IL-8 can be attributed to the interaction between beneficial bacteria, enhanced by postbiotics and intestinal enterocytes and immune cells of the lamina propria (Galdeano & Perdigon, 2006). Similarly, Kareem et al. (2016) reported reduced cytokine expression in broiler chickens supplemented with various combinations of postbiotics and inulin. Moreover, Wang (2017) documented that the supplementation of probiotic B. subtilis in the diets of broilers under heat stress decreased the expression levels of IL-6 and TNF-alpha, while increasing the IL-10 expression level. Inflammatory cytokines, especially TNF-alpha, IL-2, IL-8, and IL-6, play pivotal roles in initiating and sustaining inflammation by macrophages. High levels of TNF-alpha can result in tissue damage, sepsis, and even death (Chong and Sriskandan, 2011). Recent supplementation with a polysaccharide-based bioflocculant extracted from B. subtilis F9 was found to inhibit the expression of TNF-alpha and IL-1, while significantly increasing IL-10 levels due to the anti-inflammatory potential of the polysaccharide-based bioflocculant (Giri et al., 2019). Previous studies have demonstrated the beneficial effect of probiotics in reducing proinflammatory cytokine production (Carey & Kostrzynska, 2013). In piglets, pretreatment of porcine epithelial cells with Lactobacillus reuteri was shown to lower the expression of TNF-alpha and IL-6 (Yang et al., 2015). Moreover, the effects of feeding commensal bacteria, such as lactic acid bacteria, have been reported to have both proinflammatory and antiinflammatory actions (Foligne et al., 2007). The high population of Lactobacillus and Bifidobacterium may play a role in anti-inflammatory cytokine expression, while the decreased pathogen load could lead to an opposite reaction (Herfel et al., 2011). Humam et al. (2021) demonstrated a significant increment in Lactobacillus and Bifidobacterium counts, a reduced pathogenic load, and downregulation of IL-8 in their experiment. The studies involving probiotics have indicated that the reduction in IL-8 secretion in intestinal epithelial cells (IEC) could occur through different pathways (Gadde et al., 2017).

Expressions of IL-2, IL-6, and IFN were not affected by the inclusion of postbiotics in the diets of broilers under heat stress. However, IL-6 expression was upregulated in broilers fed with a combination of postbiotics and inulin (Kareem et al., 2016), and in lambs fed with postbiotic RG14 (Izuddin et al., 2019). Lower cytokine expression for pro-inflammatory cytokines could result from a decreased pathogen load. Lactic acid, the predominant end product of Lactobacillus fermentation, acts as an antimicrobial by inhibiting the growth of pH-sensitive, gram-negative bacteria, including pathogenic species like E. coli O157:H7 (Momose et al., 2008). Hosono et al. (2003) reported that ex vivo culture of immune cells isolated from Peyer’s patches of fructo-oligosaccharide-fed mice resulted in increased concentrations of total IgA, IL-5, IL-6, and IL-10 compared to mice without supplementation. mRNA of interleukins, lipopolysaccharide-induced tumor necrosis factor-alpha factor LITAF, and interferon (IFN) was significantly down-regulated in birds fed the positive control and combinations of postbiotic and inulin. This observation could be due to the increase in the population of Bifidobacterium in birds fed combinations of inulin and postbiotics. These observations corroborate those of Herfel et al. (2011), who reported that lower-level polydextrose as a substitute for oligosaccharide supplementation increased Lactobacillus-associated lactic acid and other antimicrobials, competitively excluding pathogenic bacteria and reducing the need for inflammation-driven cytokine production. In young pigs, a lack of overall intestinal microbial diversity, but an increased abundance of Lactobacilli, is associated with decreases in the expression of IFN-inducible genes and IL-8 (Mulder et al., 2009). Postbiotic treatments modulated the immune response against NDv, HPAIv, and IBDv vaccines, and improved bursa of Fabricius/body weight ratios were observed in postbiotic-treated chickens compared to non-treated chickens (Abd El Ghany et al., 2022). E. coli infection is known to be an immunosuppressive pathogen in poultry (McGruder & Moore, 1998), damaging the immune system of chickens and causing lymphocyte depletion in both bursa and thymus tissues (Nakamura et al., 1990). Infection of chickens with E. coli before vaccination with the IBDv vaccine resulted in a greater decrease in ELISA antibody titers compared to vaccinated non-infected chickens (Hegazy et al., 2010). Postbiotic metabolites mixture of Pediococcus acidilactici, L. reuteri, Enterococcus faecium, and L. acidophilus was found to stimulate the immune response in C. perfringens-infected broiler chickens compared to non-treated broilers (Johnson et al., 2019). Components of cell wall and cytoplasmic extracts of numerous Lactobacillus (L.) species have been identified as highly effective postbiotics (Cicenia et al., 2016).

EFFECTS OF POSTBIOTICS ON ANTIOXIDANT ENZYME ACTIVITIES

Oxidative stress triggers the production of various reactive oxygen species (ROS), such as hydroxyl free radicals and superoxide anions. Accumulation of ROS has been implicated in damaging biological macromolecules, such as proteins and nucleic acids, leading to the development of diseases (Bai et al., 2017). In poultry, the key antioxidant enzymes include GPx, SOD, CAT, and glutathione (GSH), which play crucial roles in transforming reactive species into nonradical and nontoxic products (Akbarian et al., 2016). Extensive research has been conducted in poultry birds to mitigate oxidative stress through the supplementation of various feed additives. Humam et al. (2021) demonstrated that heat-stressed chickens supplemented with different levels of RI11 (excluding 0.2%) exhibited increased GPx activity, with no difference between the 0.2% RI11 and oxytetracycline groups. However, higher levels of RI11 were required to effectively enhance GPx activity in broiler chickens under heat stress. SOD activity remained unaffected by various treatments, while CAT and GSH activities were significantly enhanced after postbiotic supplementation with 0.4, 0.6, and 0.8% RI11. This finding aligns with study conducted by Wang et al. (2018), which indicated that probiotic feed supplementation increased CAT, GPx, and SOD activities in broilers on day 21, contributing to the beneficial effects on broiler health and growth performance. Bai et al. (2016) reported that feeding broilers with the B. subtilis probiotic increased the activities of GPx and GSH, along with their mRNA expression levels. Similarly, two studies reported increased activities of CAT, GPx, GSH, and SOD in broilers under heat challenge (Altan et al., 2003; Yang et al., 2009). Thus, dietary postbiotic RI11 could improve antioxidant activities, particularly GPx, CAT, and GSH concentrations, in the plasma of broilers. Postbiotics represent a natural source of antimicrobials and antioxidants, safely alleviating stress and enhancing animal health. As postbiotics possess probiotic characteristics (Loh et al., 2014; Kareem et al., 2017; Foo et al., 2019; Gao et al., 2019; Humam et al., 2019; Izuddin et al., 2019), probiotic studies can provide valuable insights into how postbiotics improve antioxidant capability and develop oxidative resistance under heat stress. Numerous studies have reported that probiotic supplementation in poultry diets reduces the adverse effects of oxidative stress and enhances antioxidant enzyme activities (Bai et al., 2017), which may reduce cell damage by inhibiting ROS production, and ultimately improving animal health (Li et al., 2019). Shen et al. (2014) reported that blood antioxidant capacities were significantly enhanced by the inclusion of the probiotic L. plantarum in the diets, promoting growth performance in broilers. Humam et al. (2019) provided the first data on the effect of different levels of postbiotics on antioxidant activities in heat-stressed broilers. Probiotics have been reported for their capacity to remove ROS and enhance broiler health under both normal (Bai et al., 2017) and high-temperature conditions (Cramer et al., 2018). Postbiotics produced by L. plantarum have the potential to reduce protein and lipid oxidation through two mechanisms, hydroxyl radical scavenging (HRS) and reducing power (RP) (Chang et al., 2021). Unlike previous studies that focused on the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) activities of L. plantarum (Izuddin et al., 2020; Riane et al., 2020), HRS measures the scavenging activity of the most reactive radical, hydroxyl radical, related to lipid peroxidation and biomolecules of cells (Xing et al., 2015). Chang et al. (2021) demonstrated that the HRS activity of postbiotics increased from 29 to 32% when produced using a control MRS medium to 31-37% when produced using formulated media. Additionally, the postbiotic exhibited an RP of 1.9-2.9 mg/L of ascorbic acid regardless of the fermentation medium used. Similar results were reported in previous studies (Yu et al., 2016; Huo et al., 2019) for RP, involving the inhibition of the oxidation process by converting hydroperoxides to hydroxyoctadecadienoic acids and iron chelators in postbiotics, which contain various intracellular antioxidants, such as pyrrole compounds (Wang et al., 2017). Moreover, studies have revealed that the antioxidant activity of postbiotics depends on mechanisms like metal ion chelating ability, antioxidant enzyme system, and antioxidant metabolites present in the postbiotic (Yang et al., 2017). Therefore, postbiotics hold promise as supplements and feed additives to prevent inflammation caused by oxidative stress-related diseases (Li et al., 2012). The antioxidant activity of postbiotics may be attributed to the formation of pyrrole and cyclic compounds identified in L. plantarum postbiotics through GC-MS analysis (Chang et al., 2021). This antioxidant activity of L. plantarum helps to scavenge and inhibit free radicals during the oxidation processes (Lee, 2002; Chen et al., 2018). In an in vitro study by Chen et al. (2018), the fermentation of papaya juice using L. plantarum produced higher antioxidant activities compared to L. acidophilus. In-feed supplementation of L. plantarum postbiotics has been documented to reduce the negative effects stimulated by hepatic injury in mice (Lin et al., 2018), and improve glutathione peroxidase (GPX) in blood serum and ruminal fluid in post-weaning lambs (Izuddin et al., 2020), as well as enhance the activities of total antioxidant capacity (T-AOC), catalase (CAT), and GPX while reducing alpha-1-acid glycoprotein (α1-AGP) and ceruloplasmin in broiler blood plasma (Humam et al., 2020). Furthermore, supplementation of L. plantarum has been shown to impede lipid peroxidation and suppress oxidative stress in serum and liver induced by aflatoxin AFB1 (Huang et al., 2017). Thus, postbiotics offer a promising natural source of antioxidants to mitigate the effects of various stressors in animals, including poultry and large animals.

EFFECTS OF POSTBIOTICS ON ANTIBODY TITRE (PLASMA IGY, IGM, AND IGA CONCENTRATIONS)

Studies investigating the impact of postbiotics on antibody titers remain limited, whereas significant research has been conducted on the effects of probiotics, prebiotics, synbiotics, and phytobiotics on antibody titers against various viral diseases in poultry birds. Probiotics, which are non-toxic and non-pathogenic microorganisms administered in adequate amounts to confer health benefits on the host through the digestive route, have been extensively studied for their effects on blood parameters, growth performance, cecal microbiota, carcass traits, and immune responses in broilers (Pourakbari et al., 2016). Probiotic species, such as Streptococcus, Enterococcus, Candida, Lactobacillus, Bacillus, Aspergillus, Saccharomyces, and Bifidobacterium have shown positive effects on various aspects, including intestinal microflora diversity, growth performance, nutrient digestibility, immunomodulation, intestinal histological changes, certain haematobiochemical constraints, carcass characteristics, and sensory attributes of broiler meat (Kabir, 2009; Pournazari et al., 2017; Souza et al., 2018). Specifically, oral administration of Lactobacillus, Bifidobacterium, and Streptococcus has been observed to increase antibody responses against the Newcastle disease (ND) vaccine (Talazadeh et al., 2016). Sarwar et al. (2019) reported that the probiotic group showed a less steep decrease in maternal antibodies against the NDV vaccine compared to the control group, suggesting that probiotics may reduce the degradation of antibodies. Moreover, the probiotic+vaccine group exhibited an increase in antibody titers, possibly due to the immunomodulation of different subsets of immune system cells. The immunomodulatory effects of probiotic bacteria may be attributed to the bioactive peptides formed during lactic acid fermentation, which can stimulate T-cell or B-cell-mediated immune responses upon interaction with pathogens and host cells (Leblanc et al., 2004; Haghighi et al., 2006). Talebi et al. (2008) also reported that simultaneous administration of probiotics and vaccination resulted in a better antibody response. In contrast, Talazadeh et al. (2016) found a significant increase in antibody titers against the NDV vaccine with aqua blend probiotics, but not against the avian influenza virus vaccine, possibly due to the differential effects of orally administered probiotics on systemic antibodies concerning specific antigens. Regarding the antibody titer against infectious bursal disease virus (IBDV), Sarwar et al. (2019) revealed that the probiotic+vaccine group exhibited a significant increase compared to the vaccine-only group. The degree of immunostimulation by probiotics depends on the number and type of probiotics used. Sarwar et al. (2023) conducted a study on layers (Fayoumi and black Australorp) supplemented with probiotics (Saccharomyces cerevisiae) against ND and IB and found improved disease resistance in hens, though no significant effect on body weight was observed due to probiotic supplementation. Antibody titers against ND and IB were higher in all treatment groups compared to the control, possibly due to an increase in serum immunoglobulin availability modulated by probiotics (Huang et al., 2004). Haghighi et al. (2006) reported a significant increase in serum antibodies in response to sheep red blood cells in probiotic-treated birds compared to control. Similarly, Kabir et al. (2004) observed a considerably high antibody response in broilers receiving probiotics, while Cheng et al. (2004) suggested that probiotic feeding enhanced certain cell-mediated immune responses in broilers by modifying macrophage activity. Additionally, Shoeib et al. (1997) found an increase in the number of follicles in the Bursa of Fabricius in a probiotic-treated group, indicating an elevated medullar plasma cell reaction. Furthermore, Abudabos et al. (2016) observed lower Newcastle disease titers after S. typhimurium challenge in all treatment groups, including controls, antibiotics, and probiotics. However, the response after week 3 varied depending on the treatment. In contrast, Sadeghi et al. (2013) found that S. typhimurium-infected birds exhibited higher antibody titers in response to Newcastle disease vaccination compared to uninfected birds. Other studies have also shown that broilers exposed to Salmonella at a young age may remain infected upon maturity and not develop significant immunity against it (Holt et al., 1999). Furthermore, probiotics have had no significant effect on the production of anti-Salmonella Enteritidis antibodies in Salmonella-challenged birds (Ribeiro et al., 2007). Microbially fermented feed has been demonstrated to augment the amount of lactic acid bacteria in the intestines of broiler chickens, hence augmenting their immune system performance (Li et al., 2020). The study carried out by Ismael et al. (2022) suggests that adding 0.625 kg/ton of Saccharomyces cerevisiae fermented product (SCFP) to the diet of broiler chickens can considerably increase the antibody titer in response to NDV vaccines when compared to control birds. These results are corroborated by findings published in Cortés-Coronado et al. (2017), Hand (2020), Tukaram et al. (2022), and Abd El-Ghany et al. (2022). However, when broiler chickens’ postbiotic supplements were incorporated in a basal diet, Danladi et al. (2022) found no significant changes between treatment groups, highlighting the significance of precise nutritional provision for an effective immunological response.

The immune system encompasses a crucial com-ponent known as B cells, responsible for synthesizing immunoglobulins (Bucław, 2016). Immunoglobulins play a pivotal role in immune regulation and mucosal defense, but their functions can be influenced by environmental stressors (Humam et al., 2019). IgM serves three essential functions: regulating subsequent immune responses, facilitating IgG production, and mounting the primary immune response against foreign antigens (Ehrenstein et al., 2000). IgA, predominantly secreted from mucosal membranes, is the most abundant immunoglobulin in mammals (Macpherson et al., 2018). It plays a critical role in safeguarding mucosal surfaces, thus impeding the entry, binding, and colonization of toxins and pathogens (Humam et al., 2019). Palm et al. (2014) have described sIgA as the most abundant colonic antigen, known as “immune exclusion.” By interacting with specific receptors and immune mediators, IgA influences a variety of protective mechanisms (Bienenstock et al., 1973). In an experiment by Humam et al. (2019), the concentration of IgG was significantly higher in the postbiotic RI11 group compared to the negative control, ascorbic acid, and RS5-supplemented groups. The postbiotic RI11 group also exhibited elevated plasma IgM levels compared to the other groups. These findings suggest that dietary postbiotic RI11 was more effective in eliciting a humoral immune response in birds under heat stress compared to other treatments. Kareem et al. (2016) similarly reported a positive effect on the humoral immune response in broiler chickens fed a mixture of postbiotics and inulin. Additionally, broilers receiving postbiotics in their feed demonstrated significantly higher levels of immunoglobulin M (IgM) and IgG compared to those given ascorbic acid (Abd El Ghany et al., 2022). The stimulation of the immune response in birds after postbiotic treatment may be related to the presence of peptidoglycan (β-glucan) in 90% of the dry weight of Lactobacilli, along with lipopolysaccharides, teichoic and lipoteichoic acids in the bacterial cell wall (Adams, 2010). Furthermore, bacterial DNA (CpG motifs) released and recognized by the host as foreign antigens, following Lactobacilli lysis or degradation by host gastric acid, has been shown to stimulate both cell-mediated and humoral immune responses (Kant et al., 2014). Danladi et al. (2022) reported that broilers fed with postbiotics and paraprobiotics exhibited a significant increase in colon mucosa sIgA, while IgM was not significantly affected by the dietary treatment at the starter phase, and IgG did not show any significant differences (p>0.05) across the treatment diets at both the starter and finisher phases. Notably, sIgA concentrations in the colon mucosa were higher in the postbiotic RI11, paraprobiotic RI11, and paraprobiotic RG11 groups. Recent studies have shown that diets contribute to the secretion of intestinal sIgA via intestinal microbiota and could be beneficial to animal health (Hand et al., 2020). Conversely, significantly higher plasma IgG levels were observed in heat-stressed chickens fed with postbiotic RI11 (0.3%) compared to other treatments (Humam et al., 2019). Furthermore, the use of oligosaccharides in broiler diets has been reported to improve immune function by increasing IgM and IgG antibody titers in plasma (Janardhana et al., 2009). Dietary supplementation of probiotics has shown a positive effect on serum immunoglobulins, which is aligned with the findings of Fathi et al. (2017), who reported improvement in IgM and cell-mediated immunity due to probiotics. The positive impact of Bacillus subtilis on enhancing antibodies against Newcastle disease in broiler chicks may be the underlying reason (Khaksefidi & Ghoorchi, 2006). Bacillus subtilis in probiotics can also enhance humoral immune responses and stimulate the host’s mucosal immune system by interacting with intestinal epithelial cells in broilers (Gheisari & Kholeghipour, 2006). The mechanism through which probiotics enhance broiler immunity may involve protecting animals from pathogen colonization by competing for epithelial binding sites and nutrients, fortifying the intestinal immune response, and producing antimicrobial bacteriocins (Burkholder et al., 2008).

EFFECTS OF POSTBIOTICS ON HEPATIC INSULIN-LIKE GROWTH FACTOR (IGF-1) AND GROWTH HORMONE RECEPTOR (GHR) GENE EXPRESSION

Hepatic IGF-1 exerts considerable influence over the function of nutritional and growth hormones (Shamblott et al., 1995). Growth hormone (GH), secreted by the pituitary gland, triggers the hepatic production of IGF-1 through the activation of GH receptors. Prior investigations have revealed that dietary postbiotics can influence the mRNA expression of IGF-1 and GHR (growth hormone receptor) in broiler livers (Kareem et al., 2016). In their study, Humam et al. (2019) validated that, under heat stress conditions, birds supplemented with postbiotics RI11 and UL4 exhibited increased IGF-1 and GHR mRNA expressions compared to the negative control group. The intricate interplay leading to the production of IGF-1 involves both local and systemic factors. In an experimental study conducted on mice, microbiota was associated with IGF-1 production (Yan et al., 2016). Following colonization with conventional microbiota, the expression of IGF-1 in the bone marrow and adipose tissue was significantly elevated, along with the expression of Runx2, a target gene for IGF-1. Additionally, in mice supplemented with SCFAs (short-chain fatty acids), which are influenced by intestinal microbiota, there was an increase in liver IGF-1 production. Chickens fed a combination of prebiotics and L. plantarum demonstrated increased fecal SCFA production (Kareem et al., 2016). The presence of beneficial bacterial components, such as Lactobacilli and Bifidobacterium, in the intestinal microbiota contributes to higher SCFA production, as has been observed in various studies involving postbiotic supplementation in broilers (Loh et al., 2014). This intricate connection between microbiota, SCFA production, and IGF-1 expression may contribute to the upregulation of circulating IGF-1 and GHR gene expression (Humam et al., 2019). External stressors, such as heat stress, can negatively impact gut microbiota and antioxidant enzyme activities, affecting the processes involved in IGF-1 production (Yan & Charles, 2018). Humam et al. (2019) noted that heat-stressed birds without postbiotic supplementation exhibited significantly lower expression of IGF-1. Thus, the expression of IGF-1 could serve as a reliable growth index in heat-stressed broiler chickens. Dietary postbiotic and inulin supplementation has been shown to influence the expression of mRNA IGF-1 and mRNA GHR in the liver (Kareem et al., 2016). This increase in IGF-1 mRNA and GHR mRNA in birds fed a specific postbiotic and inulin combination (T6) reflects their growth performance. Notably, the level of IGF-1, feeding level, and growth rate are interrelated factors (Beckman et al., 2004). Studies have demonstrated the significance of hepatic IGF-1 production in modulating nutritional and growth hormone responses (Moriyama, 1995; Beckman, 2011). IGF-1 has been recognized as an indicator of growth rate in chickens by various authors (Jones & Clemmons, 1995; Beccavin et al., 2001). However, the ability of hepatic tissue to respond to GH is modulated by the overall nutritional status of the animal (Beckman, 2011). The development of IGF-1 as a growth index, and its level, can be influenced by various factors and situations that impact the primary processes controlling IGF-1 production. While some studies have shown a significant and positive correlation between plasma IGF-1 levels and growth rates in certain species (Beckman et al., 1998), others have not consistently demonstrated such relationships (Nankervis et al., 2000), leading to uncertainties regarding the consistency of IGF-1 growth associations.

EFFECTS OF POSTBIOTICS ON BLOOD BIOCHEMISTRY

The physiological response of an animal to its internal and external settings, such as food and nutrition, is reflected in its haematological contents (Madubuike & Ekenyem, 2006). The level of heart, liver, and kidney health as well as the requirements for amino acids and the quality of the protein in farm animals are all assessed using serum biochemical analysis (Etim & Oguike, 2011). Blood parameters are informative indicators of an animal’s physiological, pathological, and nutritional status, with changes in these parameters offering insights into the impact of dietary factors and additives on living organisms (Kang et al., 2015). Several studies have investigated the effects of feed additives as alternatives to antibiotics on the blood biochemistry of poultry birds. For instance, Haque et al. (2017) discovered that group control exhibited the highest total cholesterol level (213.00±1.78 mg/dL), whereas Yogurt showed the lowest (191.00±1.84 mg/dL). Similarly, the highest triglyceride level (120.16±1.51 mg/dL) was observed in the control, and the lowest (96.50±1.83 mg/dL) was seen in Promax. The control group demonstrated significantly higher HDL (high-density lipoprotein) value compared to all other treatment groups. The utilization of postbiotics may increase the population of lactic acid bacteria, promote the production of enzymes that disintegrate bile salts and de-conjugate them in the gut, and reduce gut pH. These factors can effectively decrease blood cholesterol by limiting the solubility of non-conjugated bile acids at low pH, leading to reduced intestinal absorption and increased excretion in the feces (Kareem et al., 2016). Probiotics have been found to decrease total cholesterol and triglycerides through enzymatic deconjugation of bile acids using bile-salt hydrolase and suppressing hydroxymethylglutaryl-coenzyme A, an enzyme involved in cholesterol synthesis (Fukushima & Nakano, 1995; Surono, 2003). Moreover, the incorporation of cholesterol into bacterial cellular membranes has also been implicated in reducing cholesterol levels (Noh et al., 1997). Humam et al. (2020) demonstrated in their study that postbiotics, especially RI11, supplemented in broiler diets under heat stress, resulted in a reduction in plasma cholesterol levels. Similar results were reported in other studies, where probiotic supplementation led to reduced total serum cholesterol levels in White Leghorn layers (Mohan et al., 1995) and broilers (Mohan et al., 1996). Conversely, the addition of antibiotics showed higher blood triglyceride and cholesterol levels (Li et al., 2007), which can be attributed to their adverse effects on fat absorption in the gastrointestinal tract (Mansoub, 2011). Regarding creatinine values, scientific studies have presented varying findings. Haque et al. (2017) reported that Renamycin® caused the highest creatinine value (3.05±0.06 mg/dL), while the lowest (0.70±0.01 mg/dL) was observed in the Yogurt-fed group. An increased level of creatinine in serum may indicate kidney damage, but significantly decreased creatinine levels were detected in probiotics-treated groups. Some probiotic microorganisms have the ability to utilize urea, creatinine, and other toxic chemicals as nutrients for growth, potentially explaining the lower creatinine levels in the blood. Hence, relatively low creatinine levels may indicate the renal protective effects of probiotics. Similarly, for AST, Haque et al. (2017) found that Ciproflox® (antibiotic) had the highest AST value (145.66±2.31 U/L), while Promax® (probiotic) had the lowest (115.00±2.30 U/L). As for ALT, the highest value (21.16±1.16 U/L) was observed in group D (Ciproflox®), and the lowest (5.36±0.38 U/L) in the probiotic group (Promax®). Both AST and ALT values decreased significantly (p<0.05) in the probiotics-treated groups compared to the control and antibiotics groups. Implementation of probiotics has been shown to lower AST and ALT levels (Santoso et al., 1995). AST is found in various organs like skeletal muscles, the heart, and the liver, while ALT is primarily sourced from the liver. The decreased levels of these enzymes may indicate less liver and skeletal muscle damage. On the other hand, ciprofloxacin use may lead to elevated levels of AST and ALT, indicating hepatotoxicity and tissue damage (Agbafor et al., 2015). Various studies have indicated that single dietary administration of probiotics or prebiotics can improve serum lipid profiles in broilers, with these supplements reducing serum TG, CHOL, and/or LDL-C levels, while increasing HDL-C levels (Velasco et al., 2010; Yalçinkaya et al. 2008). Serum lipid profiles are essential in evaluating results directly related to animal health and meat quality (Fletcher, 2002). Meat from broilers fed diets supplemented with non-antibiotic feed additives is more suitable for poultry markets due to its beneficial effect on human health (Ghasemi & Taherpour, 2013).

POSTBIOTICS UTILIZATION IN FOOD PACKAGING AND BIOPRESERVATION

The use of biological agents (e.g. bacteria and their metabolites, phages, enzymes, or naturally occurring antimicrobials) to preserve and prolong the shelf life of perishable food is known as “biopreservation” (Lücke, 2023). Biopreservation represents a viable way to meet the rising demand from consumers for premium, natural food items. Moreover, biopreservatives reduce food deterioration while preserving the flavor and nutritional value of many foods (Udayakumar et al., 2022). One efficient form of biopreservation is the use of live microbes or their metabolites to preserve food. In food, the gastrointestinal tract (GIT), culture media (or fermentate), beneficial microorganisms-probiotics, in particular, such as LAB, Bifidobacterium spp., S. cerevisiae, and Bacillus spp.-produce postbiotics (Teame et al., 2020; Vallejo-Cordoba et al., 2020). Postbiotics are made up of a complex mixture of organic acids, bacteriocins, exopolysaccharides (EPS), bioactive peptides, enzymes, and other ingredients (Moradi et al., 2020). Postbiotics may be used in the food industry in a number of ways, such as the creation of functional foods, or as biofilm removers and inhibitors (Amiri et al., 2021). Postbiotics can also be added to food formulations and packaging materials to guarantee food safety and quality. According to Abbasi et al. (2022), the food industry has adopted a novel method by incorporating postbiotics into functional foods. This approach has the potential to improve immune function and provide substantial health advantages. According to de Almeida et al. (2022), raw chicken sausages and semifinished chicken products can have their expiration date extended by using potentially postbiotic-containing preservatives (PPCP), which are made in a semiculture fermentation system with Lacticaseibacillus paracasei DTA 83 and Saccharomyces cerevisiae var. boulardii 17. When chicken products were incubated in pairs at two distinct temperatures and collected at various times, microorganisms linked to the spoiling of those goods were encouraged to proliferate. More than 3.0% of PPCP was added, and the in vitro experiment demonstrated complete inhibition of microbial growth. The findings showed that the suggested expiration date for naturally derived compounds might be prolonged through cold chain management and the co-use of PPCP in chicken products, suggesting an alternate food preservation technique. Since postbiotics contain a variety of antimicrobials, including organic acids, bacteriocins, exopolysaccharides, and bioactive peptides, they can be easily incorporated into food formulations and packaging materials. Postbiotics can be used in both liquid and dry forms. Postbiotics can therefore limit the development of infections and spoiling bacteria, prolonging the shelf life of food items. Given their ease of manufacturing and lack of need for intensive processing, postbiotics are thought to be a safer and more environmentally friendly alternative to synthetic preservatives, which can have detrimental effects on the environment. Furthermore, food producers don’t need to make any major changes to their recipes to incorporate postbiotics (Sharafi et al., 2023). According to Toushik et al. (2022), food processing facilities are highly dangerous due to foodborne pathogen-mediated biofilms. Natural compounds that possess antibacterial capabilities and are classified as generally regarded as safe (GRAS) are the disinfectants of the future for the food sector, as they promote consumer and environmental safety. This study looked at the effectiveness of plant-derived essential oils (EO) and bioactive, soluble metabolites from lactic acid bacteria (LAB) as biocidal agents. Vibrio parahaemolyticus, Pseudomonas aeruginosa, and Escherichia coli were the three pathogenic microbes against which the postbiotic generated by the kimchi-derived Leuconostoc mesenteroides J.27 isolate was tested for antimicrobial activity by looking at its metabolic components. When the minimum inhibitory concentration (MIC) of postbiotic and EO was determined against three pathogens, it was found that the sub-MIC (0.5 MIC) of these two substances could effectively prevent the formation of biofilms on surfaces used for processing seafood, such as low-density polyethylene plastic and rubber, as well as on seafood (squid). Furthermore, the polymerase chain reaction (PCR) study verified the presence of bacteriocin- and enzyme-coding genes in the LAB J.27 isolate. The generated postbiotic’s residual antibacterial activity persisted over a wide pH range (pH 1-6); however, at neutral or higher pH values, it completely vanished. Nevertheless, storage for 30 days and exposure to high temperatures (100 and 121 °C) had no effect on the activity. Notably, after treatment with postbiotic with thymol as opposed to postbiotic with eugenol, the pathogens’ intracellular metabolite leakage, DNA damage, and down-regulation of biofilm-associated gene expression were dramatically enhanced (p>0.05). As a “green preservative” for the seafood sector, combining Leu. mesenteroides J.27-derived postbiotic with both EO was suggested by all in vitro data to potentially prevent the growth of pathogenic bacteria biofilms. The antibacterial properties of postbiotics on chicken drumsticks were investigated in vitro by İncili et al. (2022). The total phenolic contents of the postbiotics (Pediococcus acidilactici (PA) and Latilactobacillus sakei/Staphylococcus xylosus (LS) were determined to be 2952.78 ± 0.4 and 1819.44 ± 0.39 mg GAE/L, respectively (p<0.05), demonstrating a high antioxidant activity. In tryptic soy broth (TSB), the amount of L. monocytogenes was reduced by approximately 5.0 log10 in 6 hours by using 5% and 10% postbiotics plus EDTA, according to the study’s findings. On the first day after decontamination with 10% PA, the count of S. typhimurium in the chicken drumstick was 2.5 log10 lower than in the control group. On the other hand, it was discovered that the L. monocytogenes levels in the chicken drumstick decontaminated with 10% Postbiotics+1% LA groups were 1.1 log10 lower than those in the control group. The 10% Postbiotics+1% LA samples had the lowest total mesophilic aerobic bacterial counts in the chicken drumsticks, and postbiotics did not alter the drumstick samples’ color on day 0 (p>0.05). According to the study’s findings, postbiotics and their mixes with naturally occurring preservatives could offer an alternate strategy for lowering the amount of food-borne viruses and extending the shelf life of chicken and pork products. In the study conducted by Serter et al. (2022), the antibacterial effects of postbiotics derived from Pediococcus acidilactici, Lactiplantibacillus plantarum, and Latilacto-bacillus sakei were investigated against a few food pathogens, including Salmonella spp., Listeria monocytogenes, Escherichia coli o157:h7, and Brucella melitensis. The bacteria were grown in sterile cow’s milk and de man rogosa and sharpe (MRS) broth. The investigation focused on the microbial count variations between the groups during the course of 17 days of storage at 4°C. After eight days of storage, it was found that the postbiotic-treated groups’ Salmonella count was 0.9 log10 CFU/g lower than that of the control and distilled water groups. While the control and distilled water groups experienced a rise in L. monocytogenes during storage, the postbiotics and 2.1% lactic acid shown a bacteriostatic impact on L. monocytogenes during this time. Additionally, 2.1% lactic acid was found to have greater decrease rates (1.8 log10 cfU/g) against Salmonella spp. when compared to postbiotics (p<0.05). Regarding the chicken breast meat’s shelf life, postbiotics increased it by 9 days, 2.1% lactic acid by 12 days, and distilled water by 5 days, all compared to the control group. Due to their ability to exhibit anti-microbial activity against pathogenic and spoilage microorganisms through a variety of mechanisms, such as the formation of cavities in CM, disruption of cell wall proteins, and reduction of bacterial cytoplasmic pH, postbiotics have been proven to be highly significant for the the food industry (Rad et al., 2021).

CONCLUSION

This article makes clear that postbiotics can be em-ployed in food, medicinal approaches, and as antibiotic growth promoters substitutes in poultry when given in sufficient levels, because of their positive influence on health. Postbiotics enhance poultry health, nutrition, and output. They might take the place of other artificial compounds and growth promoters made from antibiotics for chicken. Their gut microbiota, immune system regulation, and pathogen inhibition capacities will guarantee safer production of meat and eggs, as well as environmental sustainability, a significant decrease in the cost of treating illnesses, and the prevention of bird losses. Postbiotics and sustainable chicken farming will ensure the safety and security of food worldwide. More investigation is required to stop the use of antibiotics in the prevention of disease, and to utilize postbiotics to reduce the presence of resistance among pathogenic bacteria. Future studies on the interactions between probiotics-postbiotics, prebiotic-postbiotic, or the interaction with other feed additives, and at different dose levels, may provide new insights into beneficial relationships, and thus enhance the quality of meat, eggs, and poultry growth.

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Publication Dates

• Publication in this collection
  01 Nov 2024
• Date of issue
  2024

History

• Received
  29 Apr 2024
• Accepted
  19 July 2024