Genetic and environmental influences on beef tenderness

Mechanical tenderness measurements of M. longissimus (LM) and M. semitendin osus (ST) were analysed from 1392 tropically adapted (Brahman, Belmont Red and Santa Gertrudis) cattle grown out and finished in both tropical and tem perate environments, and 2408 temperate breed (Angus, Hereford, Murray Grey and Shorthorn) cattle grown out and finished in a temperate environment. G roups of cattle from both environments were managed under 2 finishing syste ms (pasture and feedlot) to market liveweights of 400, 520 (steers and heif ers) and 600 kg (steers only). Carcasses were electrically stimulated and c are was taken to minimise stress before slaughter. Estimated genetic variation (GV) of compression of unaged LM and ST muscles was 0.006 and 0.018 kg(2) respectively in tropically adapted and 0.004 and 0.009 kg(2) in temperate breeds (phenotypic means 1.7, 2.1, 1.6, 2.1 kg; h eritabilities, h(2) = 0.16, 0.24, 0.10, 0.16). Estimated GV for LM and ST s hear force was 0.24 and 0.12 kg(2) in tropically adapted and 0.06 and 0.02 kg(2) in temperate breeds (means 4.3, 4.6, 4.0 and 4.7 kg; h(2) = 0.38, 0.4 0, 0.11, 0.06). Genetic correlations among shear and compression forces of the ST and LM ranged from 0.28 to 0.95 in tropically adapted and -0.20 to 0 .60 in temperate breeds. The fixed effects model (market, finish, breed, bi rth herd, management group and interactions) explained about half the varia tion in compression measurements, but only 16% and 27% of the variation of LM shear force in tropically adapted and temperate breeds. The relatively low genetic variation and inconsistent genetic correlations in temperate breeds suggest genetic improvement in tenderness may be less i mportant than effective pre- and post-slaughter management protocols. The h igher additive genetic variances and moderate heritabilities in tropically adapted breeds suggest genetic improvement is possible but this will be mos t effective if combined with effective control of slaughter protocols.