Optimising dietary energy and amino acid levels in the diets of naked neck broilers for growth, nutrient utilisation and immune response in a hot climate

Abstract

AbstractThe need for a critical amino acid (AA) profile for growth, immune response and N utilisation of naked neck broilers during summer was studied. Day‐old naked neck chicks (n = 198) from a single hatch were distributed into 24 groups (four dietary regimens (DRs) with six replicates each) having eight birds in each replicate. The first diet was based on crude protein (CP) and metabolisable energy (ME) (13.40 MJ) as per NRC recommendations (DR1). In the second diet, the CP content was reduced through supplementation of synthetic AAs to achieve critical AA contents as suggested by NRC with 13.40 MJ ME (DR2). In the third diet critical AAs were supplemented to achieve their level at 108% of NRC with 12.6 MJ ME (DR3), while in fourth diet critical AA concentration was reduced to 94% (DR4) of NRC with 12.6 MJ ME to match the ratio of ME to AA concentration as that of NRC (1994). Diets were formulated separately for starter (0–3 weeks) and finisher (3‐6 weeks) phases. A metabolism trial was conducted at the third week of age. At 3 and 6 weeks of age eight birds (four of each sex) per treatment were killed to study the growth of immune organs (Bursa of Fabricius, thymus and spleen). Immune response was studied at the fourth week of age. During the starting phase, the birds fed DR1 and DR2 having 13.40 MJ ME kg−1 diet had higher body weight (P < 0.044) gain (P < 0.048) and better feed conversion ratio (FCR) (P < 0.001) as compared to DR3 and DR4 (12.6 MJ ME kg−1 diets). However, better (P < 0.001) CP efficiency (CP intake kg−1 gain) and lower feed cost kg−1 gain (P < 0.001) was recorded in DR4. A similar trend was also observed during the finisher phase. Dietary regimens had no effect on dry matter (DM) metabolisability, N intake or output and N retention. There was no difference in the weight of immune organs (bursa, thymus and spleen) between dietary treatments at either 3 or 6 weeks of age. The cell mediated and humoral immune response was also not different between the NRC and modified NRC levels. Copyright © 2007 Society of Chemical Industry