INFLUENCE OF CASTRATION AND POSTNATAL ENERGY RESTRICTION ON THE CONTRACTILE AND METABOLIC CHARACTERISTICS OF BOVINE MUSCLE

Twenty-four Montbeliard calves were raised with milk replacer to achie ve a high or low rate of gain, 1 167 and 658 g/d, respectively. At 146 kg, the animals were weaned and 6 calves from each group were castrat ed. Thereafter, and until slaughter, animals of the same weight receiv ed the same diet in both groups. Biopsy samples of Semitendinosus (ST) muscle were taken in all animals at 140 kg, 305 kg, and at slaughter, 541 kg. The biochemical, contractile and metabolic characteristics of the ST samples were analyzed. The results showed that castration at t he age of 4 months had a significant effect only on muscle characteris tics measured at slaughter, 13 months after castration. The muscles of the steers contained smaller fibers, fewer type IIA fibers and more t ype IIB fibers than those of the bulls. In contrast, feed restriction before weaning resulted in changes to fiber characteristics after wean ing at 305 kg. Restricted animals had smaller muscle fibers, a lower p ercentage of type I fibers and a higher percentage of type IIB fibers than animals fed ad libitum. These changes were no longer observed at slaughter.