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 d ietary protein (23% and 19% CP) levels. Significant sire by protein interac tions for body weights at 21, 28 and 35 days of age but not at other ages o f measurements, suggested that there is variation among environments and ag es in expression of genes associated with juvenile growth. Feed efficiencie s at 21, 28 and 35 days of age were superior for chicks fed a 23% CP diet t han 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 da ys but not at 5 days after inoculation than those fed the lower protein die t. Results suggested that in poultry breeding programmes, selection of bree ding stocks for the expression of maximum number of useful genes in desired direction may be influenced by the diet fed and age.