The Response of Broiler Chickens to Dietary Soybean Meal Reduction with Glycine and Cysteine Inclusion at Marginal Sulfur Amino Acids (SAA) Deficiency

Simple Summary

Climate change, resource shrinkage, and greenhouse gasses emission are becoming a major issue that could be confronted by using reducing protein levels in poultry diet. Reduced protein with amino acids supplementation improved the overall performance of broiler chickens. Reduced protein diets with glycine supplementation could be the potential solution to maintain the growth performance of the chicken, thus reducing feed cost and nitrogen excretion.

Abstract

The responses of broiler chickens to dietary protein reduction were investigated in the presence of glycine and cysteine inclusion at the marginal deficiency of sulfur-containing amino acids. A total of 432 broiler chickens were allotted to six dietary treatments; SP1 is standard protein diet with 100% total sulfur amino acids (TSAA), SP2 is standard protein diet with 85% TSAA, RP is reduced protein diet without glycine and cysteine supplementation, RPC is reduced protein diet with cysteine supplementation at 0.1%, and RPG is reduced protein diet with 1% glycine supplementation, while RPGC is reduced protein diet with 0.1% cysteine and 1% glycine supplementation. In this study, 4.5% protein is reduced in diets—thus, 17.5% CP (crude protein) for starter phase and 15.5% CP for the grower phase. Reduced protein diets contained 85% TSAA. Broiler chickens fed standard protein diet SP2 had superior bodyweight (BW) (p ≤ 0.05) in the starter and grower phase, average daily gain (ADG) (p ≤ 0.05) in the starter and entire feeding period, average daily feed intake (ADFI) (p ≤ 0.05) in the starter phase, and better feed conversion ratio (FCR) (p ≤ 0.05) in the starter, grower and entire feeding period; however, RPGC showed higher ADG (p ≤ 0.05) in the grower phase, and ADFI (p ≤ 0.05) in the grower and entire feeding period. RPC and RPG diet improved BW (p ≤ 0.05), ADG (p ≤ 0.05), ADFI (p ≤ 0.05), and better FCR (p ≤ 0.05) in starter, grower, entire feeding period compared to RP. The RPGC group had higher BW (p ≤ 0.05), ADG (p ≤ 0.05), ADFI (p ≤ 0.05) and better FCR (p ≤ 0.05) compared to the RPC group. Blood biochemical parameters showed that Broiler chickens fed on the SP2 diet had higher levels of total protein (TP) (p ≤ 0.05), albumin (ALB) (p ≤ 0.05), creatinine (CRE) (p ≤ 0.05), and aspartate aminotransferase (AST) (p ≤ 0.05) and, lower level of uric acid (UA) (p ≤ 0.05), blood urea nitrogen (BUN) (p ≤ 0.05), glucose (GLU) (p ≤ 0.05), and alanine aminotransferase (ALT) (p ≤ 0.05) in the starter phase; however, higher level of TP (p ≤ 0.05), GLU (p ≤ 0.05), CRE (p ≤ 0.05), and AST (p ≤ 0.05), and lower level of ALB (p ≤ 0.05), UA (p ≤ 0.05), and ALT (p ≤ 0.05) in the grower phase; RPGC had higher level of TP (p ≤ 0.05), UA (p ≤ 0.05), GLU (p ≤ 0.05), ALT (p ≤ 0.05) and AST (p ≤ 0.05), and lower level of ALB (p ≤ 0.05), BUN (p ≤ 0.05), and CRE (p ≤ 0.05) in the starter phase; however, in grower phase, RPGC had higher level of TP (p ≤ 0.05), and ALB (p ≤ 0.05), and lower level of UA (p ≤ 0.05), CRE (p ≤ 0.05), ALT (p ≤ 0.05), and AST (p ≤ 0.05). Free amino acids profile showed that broiler fed on standard protein diet SP2 had reduced the methionine (p ≤ 0.05) concentration; RPC increased the concentrations of taurine (p ≤ 0.05), phosphoethanolamine (p ≤ 0.05), threonine (p ≤ 0.05), valine (p ≤ 0.05), isoleucine (p ≤ 0.05), phenylalanine (p ≤ 0.05), ornithine (p ≤ 0.05), and lysine (p ≤ 0.05) and reduced the citrulline (p ≤ 0.05) concentration; RPG increased the concentration of glutamate (p ≤ 0.05), glycine (p ≤ 0.05), cysteine (p ≤ 0.05), and arginine (p ≤ 0.05), and decreased the concentration of tyrosine (p ≤ 0.05); and RPGC increased the concentration of serine (p ≤ 0.05) and reduced the concentration of hydroxyproline (p ≤ 0.05). Serum metabolites analysis showed that reduced protein downregulated the 54 metabolites; however, glycine fortification up-regulated the Benzamide, Pro-Ser, N-Carbamylglutamate, D-gluconate, and Gamma-Glutamylcysteine. Carcass quality showed that SP2 decreased the abdominal fat percentage (p ≤ 0.05). Nitrogen digestibility was higher by the diet RP (p ≤ 0.05). This study demonstrated that protein content could be reduced up to 4.5% with 1% glycine and 0.1% cysteine fortification in diet, which has the potential to inhibit the adverse effect of reduced protein and attain the standard growth performance.

Using crystalline amino acids to supplement broiler chicken requirements in reduced protein diets

Reducing dietary CP can reduce N pollution. Much research has been reported in corn-based diets; however, the amino acid (AA) profiles of wheat-based diets differ. Poor performance as a result of reduced protein (RP) has been overcome in corn-based diets with essential AA and glycine (Gly) supplementation. The current study examined RP levels and Gly in wheat-based diets. An industry standard protein (SP) diet plus 3 RP diets with and without Gly supplementation, to match the SP treatment at 0.713 and 0.648% digestible Gly for the grower and finisher periods respectively, were fed to male broilers from day 10 of age. Grower CP included 22.5, 20.6, 18.3, and 17.7% (days 10–21) and finisher CP included 19.7, 17.8, 16.2, and 15.5% (days 21–35). Performance, meat yield, N efficiency, water intake, and apparent ileal digestibility of N and AA were measured. No difference in body weight gain (BWG), feed intake, or feed conversion ratio (FCR) were observed at 20% CP compared to the SP treatment. However, further reducing protein reduced BWG (P < 0.001), feed intake (P < 0.001), and increased FCR (P < 0.001). Supplementation of 0.713% Gly in the grower period increased BWG (P < 0.001) and reduced FCR (P < 0.001). Relative meat yield was not affected by dietary protein, however reducing CP increased relative fat pad weight (P < 0.001). Nitrogen efficiency increased with decreased CP in both grower (R² = 0.69) and finisher (R² = 0.80) treatments. Water intake decreased (R² = 0.83) with decreasing CP intake. Apparent ileal digestibility of AA and N were higher in RP diets (P < 0.05). The benefits of reduced water intake and increased N efficiency and the disadvantages of poor performance and increased body fat in RP corn-based diets have been identified in RP wheat-based diets. Furthermore, at 18.5% CP the supplementation of crystalline AA and Gly can maintain BWG and FCR observed in SP diets.

Performance, intestinal permeability, and gene expression of selected tight junction proteins in broiler chickens fed reduced protein diets supplemented with arginine, glutamine, and glycine subjected to a leaky gut model

Changing dietary protein and amino acids may impact intestinal barrier function. Experiments were conducted in broiler chickens to evaluate supplementation of L-glutamine, glycine, and L-arginine in a reduced protein (RP) diet. Experiment 1 examined the growth performance of broilers fed 5 dietary treatments: 1) a standard diet; 2) an RP diet (193.9 g/kg CP in grower and 176.9 g/kg CP in finisher); 3) RP diet supplemented with 10 g/kg L-Gln; 4) RP diet supplemented with 10 g/kg Gly; 5) RP diet supplemented with 5 g/kg L-Arg. Each experimental diet was replicated 6 times with 10 birds per replicate. In a subset of 96 birds, experiment 2 tested the 4 RP diets with and without dexamethasone (DEX) to induce leaky gut. Each diet was replicated 24 times. Fluorescein isothiocyanate dextran (FITC-d) was used to test intestinal permeability (IP). Gene expression of selected tight junction proteins in ileal and jejunal tissues was assayed by quantitative PCR. From day 7 to 35, the RP diet increased feed intake (FI) (P < 0.05) and body weight gain (BWG) compared with the standard diet while Gln reduced FI and BWG (P < 0.05) compared with RP. Gly had no effect on BWG or FCR. Supplementation of Arg improved FCR from day 21 to 35 and day 7 to 35. In experiment 2, Arg tended to lower FITC-d (P = 0.086). DEX increased passage of FITC-d into the serum (P < 0.001). The villi surface area was increased in birds fed higher Arg (P < 0.05). DEX and diet interacted (P < 0.01) for jejunal claudin-3 mRNA level where DEX upregulated claudin-3 for all diets except the Arg diet. In summary, with a moderate reduction of protein, satisfactory performance can be obtained. Although Gln and Gly had no demonstrable positive effect on IP and performance of broilers, increasing the dietary Arg by approximately 140% improved FCR and showed indications of improved intestinal barrier function of birds fed an RP diet under a stress model.