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

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.

Influence of increasing glycine concentrations in reduced crude protein diets fed to broilers from 0 to 48 days

“…In experiment 2, birds fed the LCP88 diet had greater absolute and relative fat pad weights than the CTL or RCP group, and increasing the concentration of tGly + Ser linearly reduced abdominal fat deposition, though the lowest relative fat pad weight of all the LCP groups was still 16% higher than that of the CTL group. These results are in agreement with Elahi et al (2020) who showed that supplementing Gly in reduced CP diets can lower fat pad deposition, but not to the level of control-fed broilers. Increasing dietary Gly or betaine (trimethylglycine) has been demonstrated to stimulate lipid oxidation and reduce fat deposition in poultry, rats, and swine ( El Hafidi et al, 2004 ; Fouad and El-Senousey, 2014 ; Zhong et al, 2021 ); however, the role of Gly on broiler lipid metabolism needs further elucidation.…”

“… Hofmann et al (2019) found Glu, Pro, Asn, and Gln plasma concentrations increased with increased tGly + Ser levels, but several other plasma AA concentrations interacted with Gly and CP levels. Although not evaluated in this study, metabolic intermediates such as the ones studied by Elahi et al (2020) and Hofmann et al (2019) could further our understanding of the upregulation or downregulation of certain pathways in response to Gly, Ser, Met, and Cys relationship and this should be considered in future studies. A limitation of the current study is that we were not able to collect blood from birds in the control groups (CTL and RCP) for comparison due to their use in another concurrent experiment.…”

Do Growing Rabbits with a High Growth Rate Require Diets with High Levels of Essential Amino Acids? A Choice-Feeding Trial

“…In broilers, ref. [ 40 ] also observed that by increasing the content of sulphur amino acids from 85% to 100% above requirements (using dietary supplementation with synthetic DL-methionine), the birds showed an increased content of cysteine in plasma, amongst other amino acids. Cysteine intestinal transport involves two carrier-mediated processes [ 41 ] that are selectively inhibited by other amino acids with small polar side chains (such as threonine) or large non-polar side chains (such as methionine).…”

Effects of different dietary threonine and glycine supplies in broilers fed low-protein diets

“…The AMEn-to-CP ratio of LP diets was nearly the same, but only the LP3 treatment resulted in a significant increase in the abdominal fat pad ratio. The use of synthetic Gly supplementation can reduce the fatness of broilers fed LP diets ( 37 , 54 , 55 ). According to studies with poultry, rats, and swine, increasing dietary Gly or betaine (trimethylglycine) has been demonstrated to stimulate lipid oxidation and reduce plasma concentrations of triglycerides and fat deposition ( 56–58 ).…”