Response of Broiler Chicks to Dietary L-Leucine Supplementation in the Starter Period

Abstract

This experiment was conducted to investigate the effects of leucine (Leu) supplementation on performance and carcass traits of broilers along with the re-evaluation of standardized ileal digestible (SID) Leu requirement of broiler chicks on days 0-14. Birds were fed seven experimental diets with SID Leu levels of 16.3 (basal), 17.3, 18.3, 19.3, 20.3, 21.3, and 22.3 g/kg. Some 280 male broiler chicks were randomly assigned to the seven dietary treatments in a completely randomized design with five replicates. Dietary SID Leu levels had significant effects on body weight gain(BWG), feed conversion ratio(FCR), carcass, and breast percentages. BWG increased (p<0.05) when the broilers fed diets with 18.3 to 21.3 g/kg SID Leu compared to the basal diet. FCR decreased (p<0.05) by dietary SID Leu levels of 18.3 to 21.3 g/kg in comparison with the basal diet. Carcass yield increased (p<0.05) by SID Leu levels of 19.3 to 21.3 g/kg. Breast percentage increased (p<0.01) when the broilers received diets with 18.3 to 22.3 g/kg SID Leu and the highest value obtained by the SID Leu level of 21.3 g/kg. Abdominal fat decreased linearly by Leu supplementation (p<0.01). Regression analysis indicated the SID Leu requirement of 18.67, 18.88, and 19.85 g/kg for BWG, FCR, and breast meat yield, respectively. It can be concluded that broiler performance characteristics, especially breast yield, improve by Leu supplementation. Based on the results, the Leu requirement of modern broilers has increased dramatically due to genetic selection for a higher growth rate.

Beta‐hydroxy‐β‐methyl butyrate‐supplemented diet for broiler chickens is more conducive to dietary protein reduction than a leucine‐supplemented diet until 21 days old

“…This indicates that the plasma and intracellular levels of leucine were below the minimum needed for protein accretion. 14,16 The decreased FI in the LPD, LLPD and HLPD groups during the starter phase indicates that FI was negatively affected by the quantity and quality of dietary protein, as aligned with a previous finding. 4 Disproportionate levels of leucine in broiler diets cause an imbalance in the ratio among BCAAs 10,11 and probably antagonistic effects on the valine.…”

“…5,9,10 Also, during the starter phase, the decrease in the FI of the LLPD broilers could have induced a deficiency of isoleucine and valine as well, which is associated with growth depression. 8 The results concerning the impacts of the LLPD treatment on the carcass and non-carcass components agreed with the findings of Kratei and Shahir, 14 who reported that dietary leucine supplementation improved carcass and breast yields. However, our results on the relative abdominal fat weight and the fat contents of the studied meats did not confirm the hypothesis that leucine plays a regulatory role in fat reduction.…”

“…However, our results on the relative abdominal fat weight and the fat contents of the studied meats did not confirm the hypothesis that leucine plays a regulatory role in fat reduction. 14,34,35 This discrepancy between the previous study and our own may be related to increasing one EAA, leading to an increased need for the next limiting EAA to avoid protein synthesis limitations and decreased growth. 5,32,34 The lack of impact of leucine on the studied parameters may also be because the leucine requirement of modern broilers has increased dramatically as a result of genetic selection for a higher growth rate.…”

“…5,32,34 The lack of impact of leucine on the studied parameters may also be because the leucine requirement of modern broilers has increased dramatically as a result of genetic selection for a higher growth rate. 14 An adverse impact of dietary HMB on the broiler performance was observed in the starter phase, in contrast to previous studies. [18][19][20] However, this was not reflected in the performances at the finisher phase and the end of the experiment.…”

“…15,19,20,37 This inconsistency among studies may be related to differences in the growth rate of the birds used and changed impacts of HMB. 14,19 The small intestine and its morphologic indices are among the tissues that respond first to nutritional intervention and critical factors. Indeed, based on the results relating the morphometric indices affecting the absorption of nutrients, 6,30 a reduction in villus height indicated a growth response, represented by lower BW at marketing age, but a higher one implied the opposite.…”