Effects of dietary energy and protein levels on growth performance and immune competence of CARI-Nirbheek chickens in tropical environments.

An experiment was conducted to evaluate the effects of graded concentrations of metabolizable energy (ME) and crude protein (CP) in diet on growth performance, serum biochemical parameters, and immune response of CARI- Nirbheek chickens under tropical environments. CARI-Nirbheek is an improved indigenous dual-purpose chicken variety developed by the Central Avian Research Institute (CARI), India, for rural backyard poultry production under tropical conditions. A total of 288-day-old chicks were randomly allotted to nine dietary treatments containing three levels of ME (2,900, 2,700, and 2,500 kcal/kg) and three levels of CP (20, 18, and 16%) in a 3 × 3 factorial design, with four replicates per treatment. Birds receiving 2,900 kcal/kg ME with 20% CP yielded higher body weight gain during the starter phase (0-4 weeks), whereas optimal growth was achieved with 2,700 kcal/kg ME and 16% CP during the grower phase (5-14 weeks). Feed intake during 5-14 weeks was increased (P ≤ 0.05) with 20% CP and 2700 kcal/kg ME, while feed conversion ratio (FCR) did not differ significantly (P ≥ 0.05) among dietary treatment groups. Serum biochemical parameters remained within physiological ranges; however, higher serum total protein was observed (P ≤ 0.05) in chickens fed 20% CP. Immune responses measured by phytohemagglutinin-P (PHA-P) and sheep red blood cell (SRBC) titres were highest (P ≤ 0.01) in birds receiving 2,500 kcal/kg ME and 20% CP. Thus, it may be concluded that a dietary regimen of 2,900 kcal/kg ME with 20% CP (0-4 weeks) and 2,700 kcal/kg metabolizable energy with 20% crude protein (0-14 weeks) supports optimal growth, immune competence, and metabolic health in CARI Nirbheek chickens under tropical environments.