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The present experiment, ‘Regional Combinations'', examined growth, and carcass- and meat-quality traits in the progeny of sires genetically diverse for fatness and meat yield when grown at different rates from weaning to feedlot entry. The present paper is the first of several papers describing results from the New South Wales site, one of four in the project. It reports the effects on growth and body composition of steers during backgrounding and feedlot finishing phases. A total of 43 sires within three carcass-class categories, defined as high potential for meat yield, for marbling or for both traits, was used, based on estimated breeding values for retail beef yield and intramuscular fat. Sires were drawn from Angus, Charolais, Limousin, Black Wagyu and Red Wagyu breeds, providing a range of carcass sire types across the three carcass classes. Matings were by artificial insemination to Hereford dams from a single herd. Steer progeny were grown at conventional (slow: ~0.5 kg/day) or accelerated (fast: ~0.7 kg/day) rates from weaning to feedlot entry weight, targeting group means of 400 kg. Accelerated and conventionally grown groups from successive calvings entered the feedlot at similar entry liveweights at the same time, then having identical management during the 100-day finishing phase before slaughter. Within finishing cohorts, fast backgrounding growth resulted in increased subcutaneous fatness at feedlot entry in steers of all carcass types. Slow growth during backgrounding resulted in faster (compensatory) growth in the feedlot in all classes and sire types. This increased the deposition of fat in slow-backgrounded steers compared with that in fast-backgrounded steers during feedlotting, and thus reduced the difference between the groups in P8 and rib fat at feedlot exit. However, there did appear to be an advantage in the level of compensation in the feedlot in favour of those sire types with a genetic propensity for faster growth. Backgrounding growth rate affected body composition and the rate of weight gain during finishing. Faster growth produced more subcutaneous fat during both backgrounding and finishing. Steer progeny groups clearly showed the expected responses in growth and body composition, on the basis of the genetic potential of their sires. [ABSTRACT FROM AUTHOR]

The steer progeny of sires genetically diverse for fatness and meat yield were grown at different rates from weaning to feedlot entry and effects on growth, carcass and meat-quality traits were examined. The present paper, the second of a series, reports the effects of genetic and growth treatments on carcass traits. A total of 43 sires, within three ‘carcass class'' categories, defined as high potential for meat yield, marbling or both traits, was used. Where available, estimated breeding values for the carcass traits of retail beef yield (RBY%) and intramuscular fat (IMF%) were used in selection of the sires, which were drawn from Angus, Charolais, Limousin, Black Wagyu and Red Wagyu breeds, to provide a range of carcass sire types across the three carcass classes. Steer progeny of Hereford dams were grown at either conventional (slow: ~0.5 kg/day) or accelerated (fast: ~0.7 kg/day) rates from weaning to feedlot entry weight, with group means of ~400 kg. Accelerated and conventionally grown groups from successive calvings were managed to enter the feedlot at similar mean feedlot entry weights at the same time for the 100-day finish under identical conditions. Faster-backgrounded groups had greater fat levels in the carcass than did slower-backgrounded groups. Dressing percentages and fat colour were unaffected by growth treatment, whereas differences in ossification score and meat colour were explained by age at slaughter. There were significant effects of sire type for virtually all carcass traits measured in the progeny. Differences in hot standard carcass weight showed a clear advantage to European types, with variable outcomes for the Angus and Wagyu progeny. Sire selection by estimated breeding values (within the Angus breed) for yield and/or fat traits resulted in expected differences in the progeny for those traits. There were large differences in both meat yield and fatness among the types of greatest divergence in genetic potential for those traits, with the Black Wagyu and the Angus IMF clearly superior for IMF%, and the European types for RBY%. The Angus IMF progeny performed as well as that of the Black Wagyu for all fatness traits. Differences in RBY% among types were generally reflected by similar differences in eye muscle area. Results here provide guidelines for selecting sire types to target carcass traits for specific markets. The absence of interactions between growth and genetic treatments ensures that consistent responses can be expected across varying management and production systems. [ABSTRACT FROM AUTHOR]