Effect of Supplementation with Valine, Isoleucine, and Tryptophan Amino Acid on Growth Performance, Carcass Traits, and Nitrogen Excretion, of Broiler Chickens Fed Low-Protein Diets

This study investigated the effects of supplementing low-protein diets with valine (Val), isoleucine (Ile), and tryptophan (Trp) on growth performance, carcass traits, blood parameters, and nitrogen excretion in broiler chickens. A total of 168 one-day-old unsexed Ross-308 broiler chicks were randomly divided into six groups: a positive control (PC) fed a basal diet, a negative control (NC) fed a low-protein diet supplemented with six essential amino acids, and four groups fed the NC diet with additional Val+Ile (5% or 10%) and Trp (5% or 10%). The results showed that the NC+5% Val+Ile group had significantly higher body weight gain (BWG) and European production efficiency index (EPEI) than the PC and NC groups at 38 days of age. The feed conversion ratio (FCR) was significantly improved in the NC+5% Val+Ile group compared to that in the PC and NC groups. Tryptophan supplementation had no additive effect on growth performance. Low-protein diets decrease nitrogen excretion and improve protein metabolism. Broilers fed the NC diet had significantly lower serum lipid profiles and higher antioxidant biomarker levels than those in the PC group. Supplementation with 5% Val+Ile was adequate to improve antioxidant biomarkers and immunoglobulins M and A compared with the controls. In conclusion, supplementing low-protein diets with 5% Val+Ile improved growth performance, serum lipid profiles, immune response, and environmental sustainability, suggesting that these diets are deficient in Val and Ile, but adequate in Trp.