Effect of postweaning growth and bulls selected for extremes in retail beef yield and intramuscular fat on progeny liveweight and carcass traits

The present study is a component of a multi-site experiment, using Bos taurus cattle generated at four locations across southern Australia, designed to examine postweaning growth pathways for progeny whose sires were extreme in retail beef yield and intramuscular fat. Treatment and interaction effects on beef production and meat quality were examined within and across sites. The present paper describes the effect of postweaning growth and sire carcass type on liveweight and carcass traits at the Hamilton site. Angus sires selected on estimated breeding values for extremes in retail beef yield (RBY%), intramuscular fat (IMF%) (estimated breeding values for IMF% are derived by using live-animal ultrasound scanning) or both and sire breed types considered to be more extreme in those traits (Limousin, and Belgian Blue for yield, and Wagyu for intramuscular fat) were joined to crossbred and straight-bred cows. After weaning, the resultant 645 steer and heifer progeny were grown on a fast and slow growth path to similar to 550 kg and slaughtered, averaging 0.68 kg/day and 22.2 months, and 0.49 kg/day and 27.8 months for growth rate and age at slaughter, respectively. Growth path, sire carcass type and sex affected carcass traits; however, there were no sire carcass type by growth treatment interactions. The fast growth-path cattle were fatter, had more intramuscular fat (measured chemically), a higher Meat Standards of Australia (MSA) USA and AUS marble score, and a higher predicted MSA eating-quality score. Progeny of Wagyu sires were lighter at weaning and slaughter and had a lower hot standard carcass weight than the other sire carcass types. The Belgian Blue and Limousin progeny had a higher dressing percentage, a higher RBY% and a lower P8 and rib-fat depth and lower IMF% than the other sire breed types. Progeny of the high RBY% Angus had a lower rib-fat depth, a lower IMF% and higher RBY% than those selected for high IMF%. There was no difference in IMF% between the Wagyu or the high IMF% Angus. Progeny from the Belgian Blue, Limousin and Wagyu had a larger eye muscle area than the other sire breeds. The results indicate that simultaneous selection for supposedly antagonistic traits of IMF% and RBY% would result in carcass having high values of both measurements. Females were lighter than steers at slaughter, had a lower hot standard carcass weight, were fatter at the P8 and rib, and had a higher marble score and IMF%, a lower yield and a lower MSA-predicted eating-quality score than did steers. There was no interaction between postweaning growth and sire carcass type. These results indicate that with the use of appropriate sire carcass types and BREEDPLAN, and post-weaning nutrition, beef producers can confidently change carcass parameters to suit market specifications.