Comparison of some properties of beef from animals homozygous or heterozygous for muscular hypertrophy

Abstract

Carcass characteristics and meat properties of fifty-eight steers and heifers heterozygous (M +) for muscular hypertrophy were compared with those of fifteen homozygous (M M) steers and heifers. The M M animals had a greater carcass weight (173 versus 162 kg) and killing-out percentage than M+ animals. Age at slaughter (298 days for M M and 304 for M +) and liveweights (280 kg, M M, versus 287 kg) did not differ significantly. Carcasses from M M animals were significantly shorter, with a greater eye-muscle area and thinner subcutaneous fat cover over the loin, than those from M + animals. M. semitendinosus (ST) muscles had similar sarcomere lengths, ultimate pH values and weight losses during cooking—80°C for 90 min—for M M and M + animals. Adhesion values, both peak force and work done, were less for ST samples from M M than M + animals, indicating that the ST of M M animals was potentially more tender. This, and other work, suggests that the mechanical properties of cooked ST samples of M+ animals are intermediate between those of M M and + + animals with the ST of M M animals being the most tender. No dark-cutting, high ultimate pH (>6·0) samples were found in the fifteen M M animals slaughtered commercially in the present experiment.