Growth, immune competence and disease resistance in diverse stocks of broiler parents reared under various energy levels

An experiment was conducted to measure growth, immune competence and diseas e resistance in chicks from four different male broiler parent lines mainta ined under three diets. The diets A, B, and C contained 2500, 2700 and 2900 kcal ME/kg of feed, respectively. In each diet for each genotype, there we re twenty-five chicks, which were randomly distributed in five replicates o f five chicks in each. At 36 days of age, chicks from two replicates in eac h genotype under each diet were injected with sheep red blood cells (SRBC), another two replicates with E. coli (serotype Oil) culture and the respons e was measured five days post inoculation. At 41 days of age, the chicks of other replicate were injected intradermally in wattle with Phytohemaglutti nin-M (PHA-M) and the thickness was measured at 12 and 24 hrs post inoculat ion. There was significant genotype by diet interaction for body weight at 28 da ys of age but not at any other ages. Similarly, there were significant geno type by diet interactions for feed efficiencies at 0-28 and 0-35 days of ag e but not at 0114 days of age. This may be attributed to differences in phy siological functions of genes when fed with various diets differing in ener gy levels. The antibody titers were significant for genotypes and for diets . Genotypes, which had the lowest body weight at 35 days of age had the hig hest antibody titers. Chicks fed high energy diet had the highest antibody titers compared to those fed other two (low and medium) energy levels. Ther e were significant differences among genotypes for SRBC titers, E. coli sco re, relative spleen weight and thickness of wattle. Energy variation in die ts could not influence the immune status except for SRBC titers where high energy (diet C) fed groups had high levels of antibody. For all the immune traits, the genotypes with low body weight exhibited a higher response comp ared to other genotypes which may be due to prioritization of resource allo cation towards immunophysiological functions.