Performance of steer progeny of sires differing in genetic potential for fatness and meat yield following postweaning growth at different rates. 2. Carcass traits

Abstract

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.

Performance of steer progeny of sires differing in genetic potential for fatness and meat yield following post-weaning growth at different rates. 1. Growth and live-animal composition

“…Thus, results of type-and class-based analyses need to be assessed in combination when making conclusions. A case in point was the large differences in weight and weight gain between the Charolais and the other types (consistent with that reported by Gregory et al 1978), and further examples are evident for the carcass traits (McKiernan et al 2009). …”

“…Effects on traits in the carcass as the endpoint are examined in a companion paper to follow (McKiernan et al 2009). …”

“…Although there were few sires only from this breed, the progeny had the lowest growth rates, which would be a major concern. The carcass traits in relation to the other sire types are discussed in the companion paper (McKiernan et al 2009), and we suggest more sires need to be sampled to provide a fair assessment of this breed type.…”

“…The results for the carcass P8 and rib fat depths collected at slaughter are also presented here to show the effect of growth during the feedlot phase on fatness. However, the main effects of treatments on carcass traits are fully discussed in a companion paper (McKiernan et al 2009). …”

“…Data were collected at the abattoir by routine procedures as described by McKiernan et al (2005). Further detail of abattoir processing and subsequent measurements will be given in the papers to follow which report results on carcass traits and meat quality from this experiment (McKiernan et al 2009;J. F. Wilkins, W. A. McKiernan, J. Irwin, B. Orchard and S. A. Barwick, unpubl.…”