Energy by sire family interactions for growth, feed efficiency, immune competence in commercial broilers

Growth, feed efficiency, and immune competence were measured in commercial broiler chicks from matings of seven sires from a coloured broiler male line and eighty four dams from a coloured broiler female line which were reared in one of the three energy diets. These diets A, B, and C had 2500, 2650, and 2800 kcal ME/kg, respectively. Sire family by energy level interactions were not significant for body weights at any ages of measurements and feed efficiencies at 0 to 14 days and 0 to 28 days but for feed efficiency at 0 to 42 days of age. Among sire families, the trend which was observed at day old body weights was not same at subsequent ages except in one sire in which the body weights were consistently superior to other sires at 14 days of age and all other ages. The chicks fed high energy diet were heavier than those fed either low or medium energy diet. For slaughter traits there were no significant differences neither among sire families nor among energy levels except or percent fat weight where significant differences were observed among various energy levels. Among sire families, the antibody titers to SRBC differ significantly but not among various energy levels. The lymphoid organs (bursa and spleen) did not differ significantly neither among various energy levels nor among various sire families. From this it may be concluded that the genetic make up of a stock plays an important role in growth of lymphoid organs and immune competence rather than level of energy in feed.