Sire by protein interactions for growth, feed efficiency and immunoresponsiveness in coloured broilers

Growth, feed efficiency and immunoresponsiveness were measured in coloured broiler chicks (1 - 43 days of age) from 4 sire families, maintained on 2 dietary protein (23% and 19% CP) levels. Significant sire by protein interactions for body weights at 21, 28 and 35 days of age but not at other ages of measurements, suggested that there is variation among environments and ages in expression of genes associated with juvenile growth. Feed efficiencies at 21, 28 and 35 days of age were superior for chicks fed a 23% CP diet than those fed a 19% CP diet. Chicks fed the higher protein diet had better persistency in antibody production to sheep red blood cells at 10 and 15 days but not at 5 days after inoculation than those fed the lower protein diet. Results suggested that in poultry breeding programmes, selection of breeding stocks for the expression of maximum number of useful genes in desired direction may be influenced by the diet fed and age.