Welfare and Production Performance of Broilers Reared at Different Stocking DensitiesABSTRACT
This experiment was conducted to evaluate the welfare and production performance of broilers reared under different stocking densities. A total of 1242 one-day-old Cobb500 broiler males were distributed randomly among four treatments with nine replicates each. The treatments consisted of different broiler stocking densities (10.41; 11.45; 12.50 and 13.54 birds/m²). The parameters evaluated were regadring production performance (body weight, body weight gain, feed intake, feed conversion ratio, uniformity, and carcass yield), animal welfare (cortisol, lactate, total protein, albumin, glucose, triglycerides, cholesterol, uric acid seric, and hemogram), and litter quality (temperature, humidity, and volatilized ammonia concentration). The broilers reared at 12.5 birds/m2 presented the best feed conversion ratio at 42 days of age. Neither the carcass traits nor the stress parameters studied were influenced by the stocking densities. It was concluded that the stocking density of 12.50 birds/m² results in the best feed conversion ratio among the studied treatments for the production cycle of 42 days.
Keywords:
Adiposity; Body composition; Bone density; Morphology, Poultry science
INTRODUCTION
The performance of the poultry industry is dependent on several factors, including the stocking density of birds, and temperature and ambient humidity (Pompeu et al., 2018). The choice of stocking density should consider the ambient temperature, the ventilation rate of the shed, the arrangement of feeders and drinkers, the ammonia level, and the type of litter.
The use of high stocking density is a strategy used to optimize the use of poultry facilities, energy for water and feed distribution, labor, equipment uses, and increase productivity per area. However, high stocking densities can result in negative effects such as decreased growth rate, feed intake, and feed efficiency among the birds (Heidari & Toghyani, 2018; Goo et al., 2019; Gholami et al., 2020; Liu et al., 2021) due to a reduction of animal well-being.
It has been found that high stocking densities increase the heterophil/lymphocyte ratio, decrease the level of glutathione (GSH), and increase the level of malondialdehyde (MDA) in liver tissue, indicating increased physiological and oxidative stress (Simitzis et al., 2012; Selvam et al., 2017). Moreover, the use of high densities can reduce the immunity of birds (Qaid et al., 2016; Law et al., 2019, Li et al., 2019), and nutrient absorption capacity, impairing the villi structures of the small intestine of broiler chickens (Li et al., 2017; Awaad et al., 2019), and causing changes in the microbial population (Law et al., 2019).
Stocking density can be expressed based on the body weight of birds per m², as well as the number of birds per m² (Sugiharto, 2022). The most used housing densities are between 33 and 42 kg/m², according to European Union guidelines (Council Directive, 2007), and 31 kg/m² according to Canadian guidelines, unless humidity and temperature are tightly controlled, reaching a maximum of 38 kg/m² (NFACC, 2016). Škrbić et al. (2009) recommended a maximum density of 30 to 35 kg/m² to ensure production, health and well-being.
The behavior and well-being of birds may be affected by the stocking density. Li et al. (2020) found that broiler feeding and drinking time, feeder and drinker visits, and duration per visit were similar across the stocking densities from 27 to 39 kg/m2. However, the authors verified that the feeder utilization ratios were higher at higher stocking densities, whereas drinker utilization ratios were higher at the lowest stocking densities. Škrbić et al. (2011b) argued that an increase in stocking density resulted in a higher frequency of incidence of leg lesions and problems with body feathering; however, the studied indicators suggested that stocking density could not be considered a factor influencing broiler welfare at 3 weeks of age.
Considering the need for food production to mitigate food insecurity, while also ensuring animal welfare, it is important to determine the best density of poultry rearing.
In the present study, we obtained data concerning the effects of stocking densities of broilers on animal welfare, production performance, litter quality, and carcass yields.
MATERIALS AND METHODS
Experimental design and bird housing
The experiment was performed in accordance with the Ethics Committee on Animal Experiments of UFG, protocol number 117/19. The experiment was carried out at the Broiler Facilities of University Federal of Goias, Goiania, Goias, Brazil (17°27’49” S latitude, 48°12’06” W longitude, 807 m altitude).
A total of 1242 one-day-old Cobb 500 broiler males vaccinated against Newcastle and Marek disease, with a body weight of 48.4 + 0.5 g, were randomly distributed among four treatments and nine replicates, totalizing 36 experimental units. The treatments comprised four broiler stocking densities: 10.42 birds/m²; 11.46 birds/m²; 12.50 birds/m² and 13.54 birds/m². Different stocking densities were obtained by using 30, 33, 36 and 39 birds/experimental unit in treatments with densities of 10.42; 11.46; 12.50 and 13.54 birds/m², respectively. The experiment lasted 42 days.
Birds were housed in 36 boxes of 2.88 m² (1.80 x 1.60 m), inside a climatized industrial broiler shed with negative ventilation system measuring 12 x 125 m. The boxes were equipped with 10 nipple drinkers each and tubular feeders. The floor was lined with reused litter (5cm of rice rusk).
The shed ambience was maintained by an automatic controller regulated to keep the temperature, ventilation, and humidity parameters within the standards suggested by the lineage manual, according to its creation phases. In the initial stages, the shed was heated by a wood heater; and the ambience was subsequently controlled through fans, exhaust fans, nebulizers, and evaporative plates. The ambient temperature was monitored daily on the control panel (Table 1).
The birds were vaccinated at 14-days old against Gumboro disease, via water. All the birds received the same diet, based on corn-soybean and formulated according to Rostagno et al. (2017). Broilers had free access to feed and water during all the experimental periods. The diets were formulated for the following rearing phases: pre-initial (1 to 7 days), initial (8 to 21 days), growth (22 to 35 days) and final (36 to 42 days) (Table 2).
Production performance and carcass yield parameters
The body weight gain (g), feed intake (g) and feed conversion ratio were evaluated at 7, 21, 35 and 42 days of age. The viability of birds was calculated as a percentage, and the index of productive efficiency (IPE) was calculated as described in Equation (1):
At 42 days of age, all the birds were individually weighted. The uniformity (%) was calculated in relation to the average body weight of the animals that are within the range of ±10% of the average weight (Equation (2)).
At 42 days of age, two birds per replicate (totaling 72 broilers) were slaughtered and the carcass yield was calculated in relation to the eviscerated body weight of the warm carcass (without blood, feathers, proventriculus, feet, head, neck, viscera, intestines, pancreas, spleen, gizzard, liver, heart and abdominal fat) as shown in Equation (3):
The analyzed cuts were breast, thighs and drumsticks, wings, abdominal fat, liver, and heart. To obtain the percentage of each cut, the weight of the cut was used in relation to the live weight, according to Equation 4:
Litter quality
To assess litter quality, the temperature (ºC), humidity (%) and volatilized ammonia concentration (ppm) were measured at 42 days. The samples were collected at the same time (9:00 am).
The litter temperature was determined by measuring at six different points inside each box, using a digital laser thermometer Belchior®.
The humidity was determined using the dry matter methodology described by Silva & Queiroz, 2002.
The volatilized ammonia concentration was measured at two points inside each box, using an ammonia detector (Senko® SP2nd NH3) at height of broilers at rest.
Parameters of welfare animal
For the assessment of welfare, the following physiological parameters were analyzed: serum levels of cortisol, lactate, glucose, albumin, total protein, cholesterol, HDL, triglycerides, uric acid, and blood count at 41 days old.
At 41 days of age, one bird per repetition was used for blood collection, totaling 36 birds. Four ml of blood were collected from each bird by venipuncture of the wing vein/ulnar vein, and placed in test tubes without anticoagulant. Of the total blood volume, 1 mL was kept in tubes with anticoagulant ethylenediaminetetraacetic acid (10% K2 EDTA) to perform the hemogram. The blood count was performed manually according to Jain (1993). Hematimetric indices of mean corpuscular volume (MCV) and mean corpuscular hemoglobin concentration (MCHC) were determined by means of indirect calculations, and blood smears stained with panoptic (Laborclin®, Pinhais/PR) were used to visualize cell morphology. Hematological analyzes were performed immediately after blood collection. The remaining 3 mL of blood was centrifuged at 4 ºC, 2000 × g for 10 min. The centrifuged serum was analyzed with a biochemical analyzer Cobas Integra® 400 Plus (Roche Diagnostic, Switzerland), based on spectrophotometry, turbidimetry, fluorescent polarization, and ion-selective potentiometry. Blood samples were used to determine the concentrations of albumin, total protein, glucose, lactate, cholesterol, HDL, triglycerides, and uric acid. Serum cortisol concentrations were analyzed using ELISA assay kits (Cayman’s Cortisol ELISA Kit), following the manufacturer’s instructions.
Statistical analysis
Data were submitted to analysis of variance (ANOVA) using a computational package ExpDes.pt, EasyAnova from Software R. The arithmetic mean and standard error of the mean - SEM (collectively for four groups) were calculated for each tested feature. The averages of performance, uniformity, carcass characteristics, litter quality, biochemical and hemogram results were compared by the Scott-Knott test at 5% of significance. The viability result was submitted to Kruskal-Wallis analysis at 5% of significance.
RESULTS
Broiler production performance and carcass yield
In the pre-starter phase, the stocking density affected the broilers performance (Table 3). The broilers reared at 11.46 and 13.54 birds/m² presented higher BWG than broilers reared at 10.42 and 12.50 birds/m³. Broilers reared at 12.50 and 13.54 birds/m² had a higher FI than broilers reared at 10.42 and 11.46 birds/m³. FCR was worse for broilers reared at 12.50 birds/m² relative to the other treatments.
In the period from 1 to 21 and 1 to 35 days, no significant differences were found for any of the evaluated productive performance variables (p>0.05) (Table 3)
The stocking density of 12.50 birds/m² improved the FCR of boilers at 42 days old (Table 3). Broilers reared at 13.54 birds/m² presented the worst FCR, indicating that the increase of density is damaging to broiler development. The Index of Productive Efficiency (IPE) was not influenced by the stocking densities studied (Table 3).
At seven days of age, the stocking density of 10.42 birds/m² resulted in the highest coefficient of variation and the lowest uniformity of broilers. In the period from 1 to 42 days, birds housed at a density of 12.50 birds/m² showed a better uniformity (Table 4).
The carcass yield and cuts were not influenced by the stocking densities studied (Table 5). The average of carcass yield in this study was 84.80%.
Litter Quality
To assess the quality of litter, temperature, humidity, and volatilized ammonia concentration in the litter were evaluated, which are important factors to ensure broiler welfare. On the 42nd day, the litter temperatures were higher for the densities of 12.50 and 13.54 birds/m², as compared to the litter of birds housed in the densities of 10.42 and 11.46 birds/m² (Table 6). No significant differences were observed between the different stocking densities evaluated on the humidity and volatilized ammonia concentration of the litter (p>0.05) (Table 6).
Animal welfare
The following physiological indicators of stress were analyzed to assess animal welfare: serum levels of cortisol, glucose, lactate, albumin, total protein, cholesterol, HDL, triglycerides, and uric acid, in addition to blood count.
A statistical difference was observed in relation to the plasmatic level of total proteins, whereby birds housed under the densities of 10.42 and 11.46 birds/m² presented the highest means of total protein (p<0.05) (Table 7).
No statistically significant differences were verified for the levels of cortisol, glucose, lactate, albumin, cholesterol, HDL, triglycerides, and uric acid between the broilers housed under the different evaluated stocking densities (p>0.05), attesting that the animals did not suffer any type of stress. The levels found were all within the expected range, which shows that the animals were in a pleasant environment that favored their well-being (Table 7).
When evaluating the blood counts, no statistical differences were observed in relation to the variables that make up the erythrogram, that is, no clinical or statistical signs of anemia and/or changes in the general health status of the birds were observed during the housing period (Table 8). However, when analyzing the leukogram, statistical differences were observed for the total leukocyte count, lymphocytes, and leukocyte/thrombocyte ratio (p<0.05). Birds housed at a density of 12.50 birds/m² showed a reduction in the concentrations of total leukocytes, lymphocytes, and in the leukocytes/thrombocytes ratio (Table 8).
DISCUSSION
Broiler production performance
The broiler performance in the pre-starter phase is important because of the positive correlation between early growth rate and slaughter weight. Lower stocking densities could favor the broiler´s access to feed and water, ensuring a superior body weight gain. However, in the present study, the broilers reared at 11.46 and 13.54 birds/m² presented higher BWG than broilers reared at 10.42 and 12.50 birds/m²; and broilers reared at the higher stocking densities (12.50 and 13.54 birds/m²) had the highest FI. The results for broiler stocking densities and their influence in broiler performance are controversial in the literature. Feddes et al. (2002) reported that broilers reared at 11.9 birds/m² consumed the least feed compared to 23.8, 17.9, 14.3 birds/m². Linhoss et al. (2021) verified that stocking density (29.3 kg/m² and 43.9 kg/m²) had no significant effect on bird performance or crop fill; and that 86% crop fill at 24 h was achieved in broilers at 14 days old. According to Li et al. (2020), the feeding and drinking behaviors of broilers were similar among stocking densities (27-39 kg·m−2), and a lower stocking density may not necessarily stimulate broiler feeding and drinking. Franco-Rosseló et al. (2022) concluded the birds housed in low stocking density showed higher BW and better FCR than those in high stocking density, which was only evident after day 28. Therefore, the type of house, the management, the control of ventilation, air removal, temperature, and feeder and drinker access are important factors in the study of storage density.
The body weight gain of broiler at 42 days old was not affect by the stocking densities studied (10.42 to 13.54 birds/m²), but the feed conversion ratio was better for the stocking density of 12.50 birs/m². Although the increase of stocking densities has been reported to decrease body weight gain in some studies (Henrique et al. 2017; Sun et al., 2017; Velo & Ceular, 2020); in the present experiment, it is possible that there were enough feeders and drinkers for the broilers, causing no competition and allowing birds to develop homogenously. The birds reared to 12.50 birds/m² were more efficient in the use of diet nutrients, because they presented lower feed intake and similar body weight gain. Sugirhato (2022) reported a high stocking density to induce intestinal mucosa damages, resulting in compromised digestive and absorptive functions in broilers.
An important variable to consider regarding competition for feeders and broiler performance is the uniformity of birds. Uniformity below 60% indicates low uniformity in the treatment, while uniformity around 70% is medium, and uniformity above 80% indicates a good level of uniformity (Cobb-Vantress, 2018). In our study, we verified that the broilers of all treatments presented medium uniformity at 42 days of age.
Carcass Yield
The carcass yield of broilers was not affected by the different stocking densities studied (10.42 to 13.54 birds/m2). The stocking densities studied were probably not high enough to result in differences in carcass parameters. Nasr et al. (2021) reported that 20 birds/m² resulted in the worst carcass, breast and thigh weight, and dressing percentage; as well as a higher cooking and drip loss of breast and thigh muscles, and the highest bacterial count compared to lower stocking densities (14 and 18 birds/m²). Kryeziu et al. (2018) reported that birds housed at medium (18 birds/m²) and low (14 birds/m²) densities had higher carcass weight when compared to birds housed at a high stocking density (22 birds/m²), as well as higher yield of breast and thigh and drumstick. Likewise, Li et al. (2019) also noticed a decrease in carcass yield with increasing stocking density. Velo & Ceular (2017) reported that high stocking densities caused decreases in body weight, carcass weight and thigh weight amounting to respectively 10.5%, 9.4%, and 16.2%.
Litter Quality
Stocking density affects the temperature of the litter, resulting in an increase of temperature with the increase of stocking density. Litter quality is associated with animal well-being and productivity. As the birds’ body mass increases, they begin to produce more heat per area. With increasing age, there is also an increase in excreta in the litter, increasing humidity and leading to more litter fermentation, which raises litter temperature and also that of the shed, harming animal welfare. Škrbić et al. (2011b) verified an increase of humidity and temperature of the litter under a high stocking density; as well as a higher incidence of foot pad lesions and hock burns in broilers at 6 weeks of age. The authors also reported that high stocking density, inadequate air circulation and high outside humidity worsen litter quality of litter and increase the incidence of foot pad dermatitis and hock burns.
For litter to be within ideal use standards, its humidity must be below 35% (Cobb-Vantress, 2018). Therefore, even when increasing the density from 10.42 to 13.54 birds/m², the litter remained in good condition. Moisture levels above 35% are already considered a critical situation, as the litter becomes “caked” and produces high levels of ammonia, causing respiratory diseases and reduced weight gain (Corkery et al., 2013).
Pepper & Dunlop (2001) reported that the concentration of ammonia can become a problem due to conditions of excessive humidity in the litter and, according to Sheikh et al. (2018), increased humidity favors the microbial decomposition of uric acid, thus increasing the concentration of ammonia, which did not occur in the present study.
Animal welfare
Birds housed at densities of 10.42 and 11.46 birds/m² had the highest means of total protein, but it was not possible to determine that there were any metabolic issues in the animals, since the levels found were within the normal range, between 2.5 and 4.5 g/dL (Harr, 2002). Likewise, Ismail et al. (2014) reported that a high stocking density (16.66 birds/m²) reduced plasma concentrations of total protein when compared to a normal density (11.90 birds/m²), while still remaining within the range considered normal (2.5 to 4.5 g/dL).
Reducing stocking density has been reported to positively affect comfort, foraging and play behaviours, indicating improved welfare (van der Eijk et al., 2022).
The stress generated by overcrowding at high densities can cause significant physiological impacts, such as increased serum concentrations of glucose, total proteins, lactate, and cortisol. Cortisol is a stress-response hormone that results in glycogen and glucose catabolism, and protein catabolism, which are associated with lactate production. These considerations serve to highlight the fact that, in the present work, birds did not show signs of physiological stress, displaying acceptable levels of animal welfare.
Škrbić et al. (2011a) concluded that stocking densities up to 16 birds/m² had no influence on biochemical parameters, glucose, and cholesterol, and that, from a physiological point of view, bird well-being was not harmed. Najafi et al. (2015) reported high stocking density to be physiologically stressful to broiler chickens, as indicated by serum corticosterone, ovotransferrin, α1-acid glycoprotein, and ceruloplasmin concentrations, and HSP 70; but not detrimental to growth performance or survivability.
According to Black et al. (2011), stressful situations lead to leukocytosis, heterophilia and lymphopenia. For this reason, it has been proposed that a way to quantify the degree of stress would be to change the heterophil/lymphocyte ratio, which in most species will increase. Unlike what was found, Silas et al. (2014) reported that a higher housing density reduced red blood cell values, possibly due to the stress of decreasing space per bird. Qaid et al. (2016) found an increase in the percentage of heterophils in the blood of chicks from 1 to 14 days of age as the housing density increased. In contrast to the heterophils, the percentage of lymphocytes significantly decreased as housing density increased and, consequently, heterophil:lymphocyte ratios also increased as housing density increased.
In summary, the stocking densities used in this research did not negatively affect the welfare of the birds up to 42 days of age, based on the physiological stress indicators analyzed. Likewise, the evaluated densities did not alter the carcass and cuts yields. The increase in density promoted greater production of live weight/m² of shed. However, in the analysis of the productive performance of the broilers, the broilers housed in a density of 12.50 birds/m² showed a better value for feed conversion ratio, caused by the lower feed intake of these birds.
CONCLUSIONS
The stocking density of 12.50 birds/m² is recommended to optimize the feed conversion ratio during the production cycle of 42 days, and the stocking densities studied did not affect the welfare of broilers.
ACKNOWLEDGMENTS
The authors would thank to CAPES/FAPEG by funding of the postgraduate scholarship of the first author.
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Data availability
Data will be available in Biblioteca Digital de Teses e Dissertações (BDTD).
Publication Dates
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Publication in this collection
01 Nov 2024 -
Date of issue
2024
History
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Received
13 Dec 2023 -
Accepted
16 May 2024
