Effect of phytase and protease combination on performance, metabolizable energy, and amino acid digestibility of broilers fed nutrient-restricted diets

ABSTRACT

Three experiments were carried out to evaluate the effect of dietary combination of different enzymes (phytase + protease) on performance, metabolizable energy, and amino acid digestibility of broiler chickens fed diets with nutritional reduction. A total of 1,400, 336, and 384 male chickens were distributed in a completely randomized design, in the experiments of performance, metabolism, and digestibility, respectively. Treatments were divided as follows: positive control (PC), negative control - NC1 (PC minus 0.16% Ca, 0.15% available P (aP), and 0.5% crude protein (CP)), NC2 (PC minus 0.16% Ca, 0.15% aP, and 1% CP), NC1 added with phytase deriving from citrobacter and protease deriving from Bacillus licheniformis (CBE), NC1 added with phytase deriving from E. coli and protease deriving from microbial fermentation (SE), NC2 added with CBE, and NC2 added with SE. A protein-free diet was included in the digestibility experiment. The nutritional restriction did not affect feed intake of birds in the first experiment; however, the restriction inhibited body weight gain and feed conversion ratio in all phases. In experiment 2, the nutritional restriction decreased AME and AMEn values, although the addition of phytase and protease in diets improved both parameters, mainly in NC2. Treatment NC2 impaired the standardized digestibility of total essential amino acids of animals subjected to experiment 3, although the addition of enzymes helped to recover the digestibility to levels similar to PC. Supplementation of phytase in association with protease is effective to improve performance, energy metabolism, and standardized amino acid digestibility of broilers fed diets with nutrient restriction.

broiler; digestibility; enzyme

1. Introduction

Some antinutritional factors observed in plant-origin ingredients, such as phytate, can limit the use of nutrients in poultry diets and reduce animal performance (Gautier et al., 2018).

Phytate is an indigestible compound capable of forming complexes with minerals and proteins, a fact that impairs their digestion and absorption (Jain et al., 2016). Its incidence in diets limits the use of minerals such as phosphorus, which plays essential role in animal development (Humer et al., 2015). In addition, it limits the use of energy, as well as amino acid digestibility, not only because it binds to nutrients, or because it hinders the access of digestive enzymes to the bolus, but also due to endogenous losses (Selle and Ravindran, 2007) caused by its aggression towards the intestinal mucosa.

Dietary supplementation with exogenous enzymes is often carried out to mitigate these effects, since they act by improving nutrient digestibility and the use of energy deriving from animal feed (Yang et al., 2010; Hahn-Didde and Purdum, 2014). Phytase is an example of exogenous enzyme often used in poultry diets. It derives from genetic changes taking place in microorganisms, mostly in fungi or bacteria belonging to fungal genera Aspergillus niger and Peniophora lycii and bacterial genus Escherichia coli (Jain et al., 2016).

Phytase acts by hydrolyzing phytic phosphorus; this process results in greater bioavailability of this nutrient, as well as of other minerals such as calcium, magnesium, potassium, and zinc, and it also improves amino acid digestibility due to release of molecules linked to hexaphosphate-inositol (Dersjant-Li et al., 2015). Protease supplementation in low-protein diets has beneficial influence on broilers’ performance (Jiang et al., 2020); however, studies focused on investigating the effect of phytase and protease combination on broiler-associated parameters remains scarce in the literature. Assumingly, phytase acts in protein solubility and digestion processes, whereas protease influences amino acid recovery rates in the intestine (Cowieson and Roos, 2016).

The hypothesis of the present study is that dietary supplementation with phytase + protease can help improve the performance of broilers fed diets with reduced nutritional levels. Thus, the objective was to evaluate the effect of combining different enzymes (phytase + protease) in broiler diets on their performance, metabolizable energy values, and amino acid digestibility.

2. Material and Methods

All procedures adopted in the current study were previously evaluated and approved by the ethics committee on the use of farm animals (Registration protocol: 0123/2019), and were in compliance with the ethical principles of animal experimentation established by the Conselho Nacional de Controle de Experimentação Animal (CONCEA). Experiments were carried out in Viçosa, Minas Gerais State, Brazil (20°45'57.19" S, 42°51'35.42" W, and 682 m altitude).

2.1. Enzymes

Combinations of enzymes produced by two different companies operating in the Brazilian market were used in the experiments. The first combination (CBE) comprised phytase-6 deriving from bacterial species Citrobacter braakii- expressed in fungal species Aspergillus oryzae, as well as protease resulting from serine protease preparation (E.C.3.4.21.), which is produced by a genetically modified Bacillus licheniformis strain. The second combination (SE) comprised phytase-6 deriving from E. coli, which was produced based on submerged fermentation and on special granulation technology, as well as thermostable protease deriving from the microbial fermentation of refined advanced strains capable of acting at wide temperature (from 35 to 42 °C) and pH (3.5-7.5) ranges.

Phytases are enzymes capable of hydrolyzing the phytic acid molecule to myo-inositol and inorganic phosphates (Pi), which consequently eliminates its antinutritional characteristic and makes it available to the animal. Phytase-6 has the ability to completely dephosphorylate phytic acid (Scottá et al., 2014). With regard to microbial proteases, the mechanism of action occurs through competition with trypsin inhibitors for active sites, which consequently reduces the activity of these factors and improves the use of protein and amino acids by the animal. However, these factors can be inactivated as well as eliminated (Aderibigbe et al., 2020).

2.2. Experimental design, diets, and animals

Experimental treatments applied in the present research comprised positive control (PC; basal diet); negative control 1 (NC1; PC minus 0.16% calcium, 0.15% aP, and 0.5% crude protein [CP]); NC1 added with CBE; NC1 added with SE; negative control 2 (NC2; PC minus 0.16% calcium, 0.15% aP, and 1% CP); NC2 added with CBE; and NC2 added with SE.

The PC diet was formulated in compliance with nutritional recommendations by Rostagno et al. (2017), and was divided into starter diet (provided to broilers at the age of 1 to 21 days) and grower/finisher diet (provided to them at the age of 22 to 42 days), based on corn and soybean meal (Table 1). The nutritional level of diets adopted in the PC was reduced in diets adopted for negative controls (Table 2). Enzymes were added “on top” to the experimental diets by considering the following values: phytases (50 g/ton) and proteases (200 g/ton).

Table 1
Ingredients and nutrient composition of experimental diets

Ingredient (%)	Starter (1-21 days)			Grower (22-42 days)
	PC	NC1	NC2	PC	NC1	NC2
Corn	50.579	54.409	56.313	50.579	62.110	63.758
Soybean meal	41.422	39.183	37.482	32.892	31.271	29.854
Soy oil	3.847	2.960	2.592	4.549	3.791	3.492
Dicalcium phosphate	1.786	0.986	0.997	1.489	0.685	0.694
Limestone	0.924	1.038	1.045	0.715	0.826	0.832
Salt	0.515	0.515	0.516	0.472	0.472	0.472
DL-Methionine, 99%	0.318	0.296	0.310	0.252	0.224	0.236
BioLis, 54.5%	0.136	0.176	0.226	0.253	0.256	0.317
L-Threonine, 98%	0.048	0.012	0.022	0.030	0.012	0.022
Vitamin supplement1	0.130	0.130	0.130	0.130	0.130	0.130
Mineral supplement2	0.130	0.130	0.130	0.130	0.130	0.130
Choline chloride, 60%	0.100	0.100	0.100	0.100	0.100	0.100
Salinomycin3 (12%)	0.055	0.055	0.055	0.055	0.055	0.055
Antioxidant (BHT)	0.001	0.001	0.001	0.001	0.001	0.001
Total	100	100	100	100	100	100
Calculated nutritional composition
Metabolizable energy (kcal/kg)	3000	3000	3000	3150	3150	3150
Crude protein (%)	23.23	22.52	22.06	20.00	19.50	19.00
Calcium (%)	0.937	0.777	0.777	0.758	0.598	0.598
Available phosphorus (%)	0.440	0.290	0.290	0.374	0.224	0.224
Sodium (%)	0.218	0.218	0.218	0.200	0.200	0.200
Digestible arginine (%)	1.460	1.404	1.404	1.224	1.184	1.145
Digestible Gly+Ser (%)	1.871	1.808	1.808	1.595	1.551	1.507
Digestible lysine (%)	1.256	1.238	1.238	1.070	1.052	1.052
Digestible Met+Cys (%)	0.929	0.893	0.893	0.792	0.756	0.756
Digestible threonine (%)	0.829	0.761	0.761	0.706	0.662	0.645
Digestible tryptophan (%)	0.267	0.257	0.248	0.224	0.216	0.209
Digestible valine (%)	0.967	0.936	0.926	0.827	0.805	0.783

• PC: positive control; NC1: negative control 1; NC2: negative control 2.
• 1 Vitamin supplement - guaranteed levels per kg of feed: vitamin A, 9,375 IU; vitamin D3, 2,375 IU; vitamin E, 35 IU; vitamin B1, 2.50 mg; vitamin B2, 6.25 mg; vitamin B6, 3.5 mg; vitamin B12, 0.015 mg; nicotinic acid, 37.5 mg; B.C. pantothenic acid, 12.5 mg; vitamin K3, 1.88 mg; B.C. folic acid, 0.875 mg; biotin, 0.088 mg.
• 2 Mineral supplement - guaranteed levels per kg of feed: selenium, 0.375 mg; manganese, 88 mg; iron, 62.5 mg; zinc, 81.3 mg; copper, 12.5 mg; iodine, 1.25 mg.
• 3 Anticoccidia.

Table 2
Analyzed composition of some nutrients from experimental diets

Nutrient (%)	PC	NC1	NC1 + CBE	NC1 + SE	NC2	NC2 + CBE	NC2 + SE
Dry matter	88.40	88.50	88.60	88.70	88.80	88.90	88.10
Crude protein	25.86	22.31	21.49	22.47	22.49	22.55	21.03
Digestible protein	24.01	20.29	19.92	21.24	20.29	21.07	19.58
Total arginine	1.84	1.49	1.44	1.49	1.49	1.51	1.39
Digestible arginine	1.75	1.39	1.35	1.42	1.39	1.43	1.30
Total phenylalanine	1.29	1.21	1.17	1.21	1.20	1.22	1.13
Digestible phenylalanine	1.20	1.11	1.10	1.16	1.10	1.16	1.07
Total histidine	0.69	0.61	0.60	0.62	0.59	0.62	0.58
Digestible histidine	0.64	0.55	0.55	0.58	0.53	0.58	0.53
Total isoleucine	1.03	1.08	1.02	1.05	1.01	1.05	1.00
Digestible isoleucine	0.96	1.01	0.97	1.02	0.94	1.01	0.95
Total leucine	2.12	1.96	1.91	1.96	1.92	1.96	1.88
Digestible leucine	1.95	1.78	1.79	1.86	1.73	1.84	1.76
Total lysine	1.69	1.44	1.41	1.48	1.50	1.57	1.43
Digestible lysine	1.58	1.33	1.34	1.41	1.39	1.50	1.34
Total methionine	0.68	0.67	0.63	0.62	0.68	0.67	0.69
Digestible methionine	0.66	0.65	0.62	0.61	0.65	0.66	0.68
Total threonine	1.04	0.89	0.86	0.89	0.94	0.91	0.85
Digestible threonine	0.95	0.79	0.78	0.83	0.82	0.83	0.77
Total valine	1.15	1.08	1.03	1.06	1.03	1.08	1.01
Digestible valine	1.06	0.98	0.95	1.00	0.93	1.00	0.93

• PC: positive control; NC1: negative control 1; NC2: negative control 2; CBE: phytase deriving from citrobacter added with protease deriving from Bacillus licheniformis; SE: E. coli-derived phytase added with microbial fermentation protease.

In total, 1,400 male Cobb 500 chicks in the age group 1 to 42 days were used to assess animal performance (experiment 1). They were weighed and distributed into seven treatments by following a completely randomized design, with 10 repetitions and 20 birds per experimental unit. Chicks were housed in masonry shed divided into 1.0 × 2.0 m boxes lined with wood shavings. Animals were subjected to 24-h light program at 32 ℃ in their first week of life. Subsequently, there was a reduction of 1 h of light daily until reaching 20 h of light and 4 h of dark, which was used until the end of the experiment. Birds had access to feed and water ad libitum throughout the experimental period; maximum and minimum temperatures inside the facilities were recorded on a daily basis by three thermometers positioned at strategic points, at birds’ height.

In total, 720 male Cobb 500 chicks were used in experiments 2 and 3. They were raised in protective circles lined with wood shavings and equipped with tubular feeders and pendular drinkers for free access to water and feed. Animals were fed the initial basal diet based on corn and soybean meal, according to recommendations by Rostagno et al. (2017). A 24-h light program was carried out at ambient temperature of 32 °C in the first experimental week; this time was gradually shortened based on recommendations in the Cobb^® strain manual.

In total, 336 chicks (14 days old) were weighed and transferred to metallic cages with two-floor compartments, which were arranged in a 68-m² room with ceiling height of approximately 2.8 m; it was done to determine apparent metabolizable energy (AME) and nitrogen-corrected apparent metabolizable energy (AMEn). Cages were equipped with nipple drinkers and chute feeders. The adopted treatments were the same as in experiment 1, but this one comprised eight repetitions and six birds per experimental unit. The diet provided to the animals was the same diet initially described in Table 1. The experimental period took place from the 14th to the 23rd day of life of chicks; we adopted five days for animals’ adaptation and five days for total excreta collection in each experimental unit—and a 12-h interval between collections. Plastic-coated aluminum trays were placed under the cages for excreta collection purposes. Collected excreta were placed in plastic bags, identified based on experimental unit, and kept in freezer until the end of the collection period. Feed intake was measured during the excreta collection period.

In total, 384 chicks (in the age group 18 to 23 days of life) were distributed in a completely randomized design, with eight treatments and eight repetitions, with six birds per experimental unit, to determine the apparent and standardized digestibility coefficients of amino acids in the diets. Treatments comprised all seven experimental feeds used in the performance experiment, as well as a protein-free diet (PFD), to determine endogenous losses (Table 3).

Table 3
Composition of protein-free diet (PFD)

Ingredient	PFD (%)
Starch	82.75
Sugar	5.00
Soybean oil	5.00
Dicalcium phosphate	1.62
Limestone	0.80
Salt	0.45
Corn cob	3.00
Mineral supplement1	0.05
Vitamin supplement2	0.13
Choline chloride (60%)	0.20
Bookmark (Celite)	1.00
Total	100

• 1 Mineral supplement - guaranteed levels per kg of feed: selenium, 0.375 mg; manganese, 88 mg; iron, 62.5 mg; zinc, 81.3 mg; copper, 12.5 mg; iodine, 1.25 mg.
• 2 Vitamin supplement - guaranteed levels per kg of feed: vitamin A, 9,375 IU; vitamin D3, 2,375 IU; vitamin E, 35 IU; vitamin B1, 2.50 mg; vitamin B2, 6.25 mg; vitamin B6, 3.5 mg; vitamin B12, 0.015 mg; nicotinic acid, 37.5 mg; B.C. pantothenic acid, 12.5 mg; vitamin K3, 1.88 mg; B.C. folic acid, 0.875 mg; biotin, 0.088 mg.

2.3. Performance, metabolizable energy, and amino acid digestibility

Body weight, feed intake, and leftover feed rates were recorded for animals (at the ages of 1, 21, and 42 days) in each experimental unit to determine body weight gain (BWG), mean feed intake (FI), and feed conversion ratio (FCR) during experimental periods 1-21, 22-42, and 1-42 days.

Excrements collected in each cage were weighed at the end of the experimental period and homogenized for the energy test. To do so, 200-g samples were pre-dried at 55 °C for 72 h and ground in ball mill (Tecnal Equipamentos para Laboratório, TE-350, São Paulo, Brazil) for 5 min, until it turned into a fine mix.

Animals subjected to the digestibility trial were slaughtered at their 23rd day of life for collecting the ileal digesta. Their abdominal cavity was opened and all intestinal contents found 40 cm away from the terminal ileum, anterior to the ileocecal junction, were removed. The ileal digesta of animals used in each repetition was combined to form a composite sample for each treatment. Ileal digesta samples were lyophilized at −40 °C for 72 h.

2.4. Chemical analysis

Diets and excreta were analyzed to determine dry matter (DM) and CP rates (AOAC, 1990). The Kjeldahl method was used to determine nitrogen levels, both in diets and excreta, based on official analysis methods (AOAC, 1990). Excreted nitrogen (EN) was calculated by multiplying the total excretion amount (in DM) by the nitrogen rate found in the excretion (also in DM). The same method was applied to calculate nitrogen consumption (NCon). Retained nitrogen (RN) was calculated by subtracting EN from NCon. Retained nitrogen rate (%RN) was calculated by considering the amount of nitrogen that was consumed. Nitrogen balance (NB) was obtained based on the amount of consumed nitrogen minus the excreted nitrogen. Gross energy (GE) values were determined by using a C5001 adiabatic calorimetric pump (IKA-Werke GmbH & Co. KG, Staufen, Germany). Values of AME and AMEn were calculated based on GE values recorded for food and excreta by using the equations described by Sakomura and Rostagno (2016):

$$\begin{gathered} \mathrm{AME}=\left({\mathrm{GE}}_{\mathrm{ing}}-{\mathrm{GE}}_{\mathrm{exc}}\right)/{\mathrm{DM}}_{\mathrm{ing}}\mathrm{and} \\ \mathrm{AMEn}=\left({\mathrm{GE}}_{\mathrm{ing}}-{\mathrm{GE}}_{\mathrm{exc}}-\left(8.22*\mathrm{NB}\right)\right)/{\mathrm{DM}}_{\mathrm{ing}} \end{gathered}$$

in which GE_ing = gross energy ingested, GE_exc = gross energy excreted, and DM_ing = dry matter ingested.

Dry matter, fecal indicator, and indigestibility factor (IF) (AOAC, 1990) of ileal digesta collected from broiler chickens were analyzed for digestibility calculation purposes. Laboratory analyses based on HPLC (high-pressure liquid chromatography) were performed to determine amino acid contents in animals’ diets and excreta. Apparent and standardized amino acid digestibility coefficient rates were calculated by using the acid-insoluble ash (AIA) indigestibility factor, based on equations presented by Sakomura and Rostagno (2016). The AME, AMEn, and amino acid digestibility coefficients were calculated based on the equations described by Sakomura and Rostagno (2016):

$$\begin{gathered} {\mathrm{CDAA}}_{\mathrm{apa}}=\left(\left({\mathrm{AA}}_{\mathrm{ing}}-\left({\mathrm{AA}}_{\mathrm{dig}}*\mathrm{IF}1\right)\right)/{\mathrm{AA}}_{\mathrm{ing}}\right)*100 \\ {\mathrm{CDAA}}_{\mathrm{sta}}=\left({\mathrm{AA}}_{\mathrm{ing}}-\left(\left({\mathrm{AA}}_{\mathrm{dig}}*\mathrm{IF}1\right)-\left({\mathrm{AA}}_{\mathrm{end}}*\mathrm{IF}2\right)\right)/{\mathrm{AA}}_{\mathrm{ing}}\right)*100 \end{gathered}$$

in which CDAA_apa = apparent amino acid digestibility coefficient; AA_ing = ingested amino acid; AA_dig = digesta amino acid; IF1 = indigestibility factor 1, IF1 = AIA_diet/AIA_digesta; IF2 = indigestibility factor 2, IF2 = AIA protein-free diet/AIA_digesta; CDAA_sta = standardized amino acid digestibility coefficient; and AA_end = endogenous amino acid.

2.5. Statistical analysis

The adopted statistical model was:

${\mathrm{Y}}_{\mathrm{ik}}=\mathrm{\mu }+{\mathrm{\tau }}_{\mathrm{i}}+{\mathrm{\epsilon }}_{\mathrm{ik}}$

in which Y_ik = value recorded for the response variable observed in the k-th repetition of the i-th level of the tested factor, μ = mean value recorded for treatments, τ_i = effect of the i-th level of the tested factor, and ε_ik = experimental error associated with the observed Y_ik value.

All collected data were subjected to analysis of variance at 5% significance level by using the ExpDes.pt package of the R statistical software (R Software v. 4.0.4). Data were subjected to Shapiro-Wilk test to determine normality of residuals; subsequently, they were subjected to analysis of variance (ANOVA). Dunnett’s test was used at 5% significance level to compare means recorded for the control treatment to those of other treatments.

3. Results

3.1. Performance

There were no differences among the treatments on FI of chickens in starter phase (from 1 to 21 days old). Negative controls showed lower BWG results, whereas enzyme addition to the diets did not lead to BWG results different from those of PC. All treatments, except for NC1 + SE, recorded worse FCR results than PC.

In the growth phase (from 22 to 42 days), there was no difference between PC and the other treatments for all variables except BWG, where NC2 was lower than CP.

There was no difference between the treatments and PC on FI for the whole experimental period (1 to 42 days). Treatment NC2 was the only to show difference in BWG during this period, recording the worst BWG results. Treatments NC1 and NC2 recorded worse FCR results than PC, whereas the other treatments did not show difference in this parameter (Table 4).

Table 4
Results observed for feed intake (FI), body weight gain (BWG), and feed conversion ratio (FCR) at all three performed experimental stages

Treatment	1 to 21 days			22 to 42 days			1 to 42 days
	FI (kg)	BWG (kg)	FCR	FI (kg)	BWG (kg)	FCR	FI (kg)	BWG (kg)	FCR
PC	1.227	1.049	1.170	3.693	2.196	1.682	4.920	3.245	1.516
NC1	1.243	0.990*	1.256*	3.698	2.157	1.716	4.941	3.146	1.571*
NC1 + CBE	1.250	1.033	1.209*	3.651	2.134	1.712	4.900	3.167	1.547
NC1 + SE	1.238	1.035	1.196	3.705	2.232	1.661	4.942	3.267	1.513
NC2	1.197	0.974*	1.230*	3.573	2.070*	1.726	4.769	3.044*	1.567*
NC2 + CBE	1.256	1.035	1.214*	3.677	2.171	1.696	4.933	3.206	1.540
NC2 + SE	1.283	1.057	1.214*	3.671	2.184	1.681	4.954	3.241	1.528
SEM	0.0068	0.0059	0.0046	0.0156	0.0115	0.0063	0.0184	0.0141	0.0044
P-value	0.3434	0.0464	<0.001	0.4843	0.0201	0.3479	0.7923	0.0489	0.0112

• PC: positive control; NC1: negative control 1; NC2: negative control 2; CBE: phytase deriving from citrobacter added with protease deriving from Bacillus licheniformis; SE: E. coli-derived phytase added with microbial fermentation protease.
• SEM - standard error mean.
• Means followed by * in the same column differ from PC, based on Dunnett's test, at 5% significance level (P<0.05).

3.2. Metabolizable energy

Treatments NC1 and NC2 recorded AME and AMEn values lower than those of PC. The addition of both enzymes to the diet provided in NC1 helped improve these parameters, which achieved values similar to those of PC. Addition of enzymes to the diet in NC2 led to higher results than those recorded for PC.

Treatments NC1 and NC1 + CBE recorded NCon similar to that of PC, whereas the other treatments recorded lower NCon values. Treatment NC1 was the only treatment recording EN similar to that of PC; all other treatments recorded lower EN values. Retained nitrogen in NC1 + CBE recorded higher values than that of PC, whereas the other treatments did not show difference in this parameter (Table 5).

Table 5
Results observed for apparent metabolizable energy (AME), nitrogen-corrected apparent metabolizable energy (AMEn), nitrogen consumption (NCon), excreted nitrogen (EN), and retained nitrogen (RN)

Treatment	Variable
	DMI (kg)	AME (kcal/kg)	AMEn (kcal/kg)	NCon (g/bird)	EN (g/bird)	RN (%)
PC	0.398	3498.70	3276.80	16.38	5.65	65.52
NC1	0.403	3243.40*	3026.00*	16.05	5.38	66.45
NC1 + CBE	0.397	3549.60	3323.00	15.82	4.65*	69.27*
NC1 + SE	0.383	3548.20	3331.50	15.22*	4.87*	66.25
NC2	0.399	3391.00*	3198.50*	14.29*	4.94*	65.42
NC2 + CBE	0.403	3625.30*	3431.60*	14.11*	4.61*	67.33
NC2 + SE	0.384	3631.90*	3441.20*	13.81*	4.91*	64.44
SEM	0.0022	18.9639	19.2461	0.1474	0.0654	0.3248
P-value	0.6139	0.0385	0.0394	<0.001	<0.001	<0.001

• PC: positive control; NC1: negative control 1; NC2: negative control 2; CBE: phytase deriving from citrobacter added with protease deriving from Bacillus licheniformis; SE: E. coli-derived phytase added with microbial fermentation protease.
• SEM - standard error mean.
• Means followed by * in the same column differ from PC, based on Dunnett’s test, at 5% significance level (P<0.05).

3.3. Amino acid ileal digestibility coefficient

Both negative control treatments impaired the digestibility of amino acids such as arginine, histidine, leucine, lysine, and threonine; these two treatments recorded amino acid digestibility results lower than that of PC; however, the addition of both enzymes to animals’ diets was capable of improving the digestibility coefficient of all the aforementioned amino acids. Nutritional reduction did not affect the isoleucine digestibility coefficient, whereas the addition of both enzymes to the investigated diets helped improve these coefficients, which reached values higher than those of PC.

Methionine digestibility was only impaired in NC2; however, enzyme addition to the diet was capable of improving this parameter. The NC2 was the only group recording total essential amino acid digestibility lower than that of PC (Table 6).

Table 6
Results observed for standardized digestibility of essential amino acids (AA)

Variable	PC	NC1	NC1 + CBE	NC1 + SE	NC2	NC2 + CBE	NC2 + SE	SEM	P-value
Crude protein	92.83	90.93*	92.70	94.53*	90.23*	93.47	93.10	0.2137	0.0335
Arginine	94.75	93.27*	94.31	95.21	92.83*	94.99	93.76	0.1508	0.0292
Histidine	92.13	90.32*	92.42	94.01*	89.49*	92.89	92.69	0.2291	0.0421
Isoleucine	93.69	94.05	95.30*	96.76*	93.17	95.76*	95.25*	0.1946	<0.001
Leucine	92.40	90.79*	93.52	94.98*	89.93*	94.04*	93.86*	0.2597	0.0227
Lysine	93.90	92.61*	94.65	95.46*	92.50*	95.59*	94.02	0.1838	<0.001
Methionine	97.89	97.64	98.07	98.71	96.13*	98.89*	98.22	0.1392	0.0376
Phenylalanine	93.17	92.07	94.01	95.46*	91.52*	94.60*	94.22	0.2045	0.0108
Threonine	91.10	88.82*	90.61	93.25	86.83*	91.51	91.03	0.3229	0.0123
Valine	91.98	91.39	92.68	94.39*	90.01*	93.23	92.24	0.2185	0.0405
Total essential AA	92.75	92.19	93.91	95.27*	91.33*	94.60*	93.88	0.2029	0.0443

• PC: positive control; NC1: negative control 1; NC2: negative control 2; CBE: phytase deriving from citrobacter added with protease deriving from Bacillus licheniformis; SE: E. coli-derived phytase added with microbial fermentation protease.
• SEM - standard error mean.
• Means followed by * in the same line differ from PC, based on Dunnett’s test, at 5% significance level (P<0.05).

4. Discussion

Significant nutritional reductions without enzyme supplementation can have negative impact on broiler performance, mainly by reducing BWG and FI, and by hindering FCR. The present study recorded decreased CP, aP, and Ca levels in the analyzed animals; these nutrients play essential role in several metabolic functions in their body. Phosphorus and calcium are essential minerals involved in several metabolic processes such as skeletal development, energy transfer, enzyme activation, and basic acid balance, among others (Jlali et al., 2020; Bavaresco et al., 2020). Protein reduction can lead to higher body fat deposition (Chrystal et al., 2020) and result in worsened weight gain and poor feed conversion.

Results observed for BWG and FCR in the stage from 1 to 21 days explain the effect of enzymes on the assessed parameters, since the reasons for using them is to make dietary nutrients available, and to improve their use, to enable better weight gain and feed conversion (Babatunde et al., 2022). The combined use of enzymes may have improved the availability and absorption of nutrients that were not available in traditional feed types, since it promoted the use of amino acids that play important role in animal growth. Among them is lysine, which plays essential role in the synthesis of muscle proteins and acts in the formation of structures such as collagen and digestive enzymes. Results recorded in the stage from 1 to 42 days were similar to each other for the same reason.

Previous studies about the use of phytase + protease have shown controversial results. According to Cowieson et al. (2019), supplementation with phytase + protease can help improve BWG and FCR, whereas Walk and Poernama (2019) showed that protease supplemented with phytase did not change animal performance results. Kamel et al. (2015) used protease in diets, presenting reduced nutritional levels, and concluded that such a supplementation improved parameters such as animal performance, villus height, and villus:crypt ratio. Proteases have proteolysis functions that are characterized by the breakdown of peptides bond of protein chain. Proteases are classified as endopeptidases or exopeptidases; in other words, they will act hydrolyzing the peptide chains in smaller molecules or hydrolyzing the carboxyl-terminal domain, releasing free amino acids, thus, improving the nutrient utilization and animal development (Sakomura et al., 2014).

Results recorded for energy metabolism can be explained by the presence of phytate in the diet, since it can limit the use of phosphorus (Dersjant-Li et al., 2015), which plays key role in energy metabolism processes. Using phytase enables higher P availability to act in energy metabolism, as seen in AME and AMEn values recorded in the current study. Using phytase can also lead to increased use of dietary energy; it mainly happens because phytase favors mucin availability due to higher cell turnover, which is triggered by its presence in the diet (Bao et al., 2013; Cowieson et al., 2017). Furthermore, phytase can act by preventing the formation of binary protein-phytate complexes through hydrolysis, by reducing endogenous protein flow and nitrogen losses, as well as by increasing nitrogen retention (Cowieson et al., 2017; Gallardo et al., 2020).

The incidence of phytate in birds’ diet leads to amino acid complexation, endogenous enzyme inhibition, and increased endogenous amino acid secretions, a fact that affects their digestibility (Bao et al., 2013). Based on results in the current study, treatments without enzyme addition showed amino acid digestibility deterioration, whereas phytase + protease addition to treatments with reduced nutritional levels improved the digestibility of all essential amino acids.

The importance of essential amino acids lies on the fact that they are not synthesized by the body fast enough to meet maximum performance requirements; thus, they must be supplied via diet, which consequently promotes their good digestibility and enables them to perform their functions in the body (Bertechini, 2012). Results observed in the current study based on phytase + protease combination can be explained by the fact that phytase has increased pepsin and trypsin activity (Murugesan et al., 2014), and the microbial protease competed with trypsin inhibitors for the binding sites, which consequently decreased the activity of these antinutritional factors and increased protein and amino acid utilization by the animal (Aderibigbe et al., 2020). These two enzymes, which play essential role in protein digestion, are inhibited by the presence of phytate in the diet. Protease acts by increasing amino acid digestibility, as well as by improving intestinal parameters, and can lead to better absorption of nutrients such as amino acids (Kamel et al., 2015).

Another factor linked to phytase addition to diet of birds lies on the fact that this enzyme is associated with lower loss of endogenous amino acids (Dersjant-Li et al., 2015; Gallardo et al., 2020). It happens because phytic acid associates with basic amino acid residues, such as lysine, arginine, and histidine, to form large insoluble aggregates when birds eat the prepared diet and reaches the gastric digestion stage. This effect encourages birds to secrete hydrochloric acid and pepsin to restore food solubility and digestibility; this process increases the need of gastric and intestinal mucin, as well as of sodium bicarbonate, to ensure intestinal integrity. Thus, the negative effect of phytic acid on amino acid digestibility is significantly associated with higher loss of endogenous amino acids in the intestine, rather than with direct impact on dietary protein digestibility. This very same factor is also linked to the use of protease in animals’ diet since, according to Cowieson and Roos (2016), protease helps reduce endogenous amino acid losses through the hydrolysis of peptide chains into smaller molecules.

5. Conclusions

The dietary combination of phytase and protease is effective to improve performance, metabolizable energy, and amino acid digestibility of broiler chickens fed nutrient-deficient diets. Although all assessed enzymatic combinations show good results, the SE combination shows better results in the majority of assessed parameters. Therefore, the SE enzymatic combination is recommended for broiler chickens fed nutrient-deficient diets.

Acknowledgments

The authors thank Suntaq Enzymes for the financial support and the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES, Brazil) for granting the scholarship to the first author.

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Publication Dates

• Publication in this collection
  25 July 2022
• Date of issue
  2022

History

• Received
  14 Jan 2022
• Accepted
  1 Apr 2022