Effect of dietary valine supplementation to low protein diets on performance, intestinal morphology and immune responses in broiler chickens

Abstract

The current trial was conducted to study effects of dietary valine (Val) supplementation in low crude protein (CP) diets on performance, gut development and immune responses in broiler chickens. A total of 540 day-old broiler chicks (Ross 308) were assigned to 6 dietary treatments, comprising 6 replicates of 15 birds based on a factorial arrangement of treatments (2 × 3) in a completely randomized design during 1–12, 12–24 and 24–42 days of experiment. Dietary treatments included 3 diets with 100% (CP100; starter:217 g/kg, grower: 200 g/kg, finisher: 180 g/kg), 90% (CP90; starter: 195.3 g/kg, grower: 180 g/kg, finisher: 162 g/kg) and 85% (CP85; starter: 184.5 g/kg, grower: 170 g/kg, finisher: 153 g/kg) of dietary crude protein requirement of Ross 308 broiler chickens each supplemented with or without Val. Valine was supplemented to CP85 and CP90 diets in order to fulfill Val requirement of Ross 308 broiler chickens in which CP85 contained 9 g/kg digestible Val in starter, 7.9 g/kg digestible Val in grower and 7.1 g/kg digestible Val in finisher periods and CP90 contained 9 g/kg digestible Val in starter, 7.9 g/kg digestible Val in grower and 7.1 g/kg digestible Val in finisher periods. However, Val supplemented to CP100 with equal magnitude supplemented to CP90 in order to offer chickens with Val beyond their requirement. (starter: 9.9 g/kg digestible Val; grower: 8.7 g/kg digestible Val; finisher: 7.9 g/kg digestible Val). Supplemental Val could restore the compromising effect of CP85 and CP90 on growth of broilers during starter and growing phases equal to broilers received CP100 (P < 0.05) while failed to ameliorate growth of broilers during the finishing and entire rearing periods. Supplementation of Val in low CP diets improved breast yield of broilers compared to those fed on CP90 and CP85 diets (P < 0.05). Villus height to crypt depth ratio was higher in broilers received diets supplemented with Val in low CP diets than those fed on CP100 (P < 0.05). Total serum antioxidant activity decreased in broilers fed with CP90 compared to those received CP100 (P < 0.05) whereas Val supplementation could not ameliorate the impaired serum antioxidant activity compared to CP100 (P < 0.05). In conclusion, dietary Val supplementation could decrease negative effect of feeding low CP diets in broiler chickens through the beneficial effect on protein accretion and intestinal morphology while failed to improve immune responses.