Response of broilers to gradual dietary protein reduction with or without an adequate glycine plus serine level

Abstract

This study was aimed to probe broiler responses to the maintenance of adequate level of glycine plus serine in low crude protein (CP) diets by glycine (Gly) addition from 8 to 42 days of age. A total of 1152 7-d-old birds were divided into 8 groups and fed with one of the following diets: (I) normal CP diet; (II, III vIV V) diets with 1.5%, 3%, 4.5% and 6% points less CP than normal diet, respectively; (VI, VII, VIII) diets with 3%, 4.5% and 6% points reduced CP than the normal CP diet, respectively, and added with Gly to achieve 2.32% total Gly þ Ser. Each treatment was replicated with 12 cages. Results showed that dietary CP reduction by 3% or higher compromised (p < .05) growth performance and carcase traits of broilers. Gly fortification in the diet with a 4.5% CP reduction produced similar accumulative growth performance relative to normal-CP group. When Gly fortification in the diet with a 6% CP reduction, the accumulative growth performance were improved (p < .05) but were still inferior (p < .05) to those in normal-CP group. Gly fortification supported a similar (p > .05) abdominal fat percentage of birds fed the diet containing 4.5% points less CP as compared with birds fed the normal-CP diet. Comparatively, Gly fortification in the diet with a 6% CP reduction resulted in breast muscle yield, serum UN content on d 21 and albumin content on d 42 comparable to (p > .05) those in normal-CP group. Collectively, the absence of Gly addition allowed dietary CP reduction by no more than 3% to obtain normal performance and carcase traits of broilers. Gly fortification in the diet with a 3% CP reduction induced no improvements in growth performance and carcase traits of broilers. However, maintain a level of 2.32% total Gly þ Ser via Gly fortification enabled a reduction of dietary CP by 4.5% without deteriorating the accumulative growth performance and carcase traits of broilers. HIGHLIGHTSGly addition that provides 2.32% total Gly þ Ser allows dietary CP reduction of 4.5% without compromising the accumulative growth performance and carcase traits of broilers. Maintaining 2.32% total Gly þ Ser via Gly fortification could not completely overcome the depression of growth performance in broilers fed the diet with a 6% CP reduction.

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

“…Moreover, glycine improved nutrient utilization and protein synthesis, thus improving growth performance [ 23 ]. This statement supports our judgment that glycine supplementation in a reduced protein diet reduced the negative effect on growth performance, which is also in agreement with Wang et al, 2020 [ 24 ]. Also, L-methionine could also be a reason for acceptable growth performance.…”

Effect of Low Protein Diets Supplemented with Glycine on Growth Performance Carcass Traits, Blood Parameters and Antioxidant Status of Mandarah Chicks During Starter and Grower Periods

“…Decreased abdominal fat and increased keel bone length. This results are in agreement with the finding of Wang et al (2020) who found that there were no significant effects due to 1.5% of dietary CP reduction on carcass traits of broilers at 21 and 42 day of age. Lowering dietary CP level by 3% significantly increased abdominal fat percentage of birds on d 42.…”

“…was the best FCR during the overall period. These results are in agreement with the finding of Wang et al (2020) who found that adding glycine to broiler chicks diet to 2.32% total glycine and Serine with a 3% reduction of crude protein level normalized the growth performance of broiler chicks and significantly improved feed conversion ratio during starter and the overall periods as standard protein diet chicks. Supplementation of glycine to the diet with a 4.5% CP reduction restored to the standard levels both of feed conversion ratio (starter period), final Body weight and overall average daily weight gain.…”

“…This results are in agreement with many researches, Zhong et al (2021) found that Diet supplemented with glycine did not affect the concentrations of ALT, AST, total protein, albumin, urea nitrogen, creatinine in pigs. In addition, Wang et al (2020) who found that lowering dietary CP level did not affect serum total protein, albumin, uric acid and creatinine contents of broilers on. Adding glycine decrease significantly serum uric acid and serum urea content.…”

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

“…These results are likely due to broilers eating to satisfy a certain nutrient need like previously recorded for the LCP-fed chicks from 0 to 14 d and such nutrients may include the lower (7.4-8.3%) analyzed tGly+Ser, Trp, or Leu from 28 to 39 d. From 0 to 48 d, broilers fed the LCP88 diet (2.38% unit average analyzed CP reduction) had the highest FCR and linear, but not quadratic, improvements in FCR were observed when increasing dietary tGly + Ser. Similarly, other studies have shown that the addition of Gly had the most impact on improving FCR ( Waguespack et al, 2009b ; Berres et al, 2010 ; Kriseldi et al, 2017 ), possibly by improving nutrient utilization and protein synthesis via enterocyte development or mucin secretion ( Powell et al, 2009 , 2011 ; Wang et al, 2020 ). A lack of a quadratic response may indicate that optimum tGly + Ser levels were not reached even at the highest level of added Gly from 0 to 48 d.…”