Effects of growth path, sire type, calving time and sex on growth and carcass characteristics of beef cattle in the agricultural area of Western Australia

摘要

Growth, carcass characteristics and meat quality of the steer and heifer progeny of autumn (AC: March–April)nand winter (WC: June–July) calving cows following weaning in January in each of 3 years (2003–05) were measured. Thencows were mated to sires with a high estimated breeding value for either retail beef yield (RBY), intramuscular fat (IMF) ornboth RBY and IMF. After weaning, the progeny entered one of three growth paths until slaughter at an average steernliveweight of 500 kg: (i) fast – fast growth from weaning on a high concentrate feedlot diet; (ii) slow – slow growth fromnweaning (~0.6 kg/day) to 400 kg liveweight followed by growth at over 1 kg/day on high quality pasture; or (iii) comp. – 10%nweaning weight loss, immediately after weaning followed by compensatory or rapid growth of over 1 kg/day on high qualitynpasture. Steers on the fast growth path had higher (P < 0.001) P8 fat thickness than those on the slow or comp. growth pathsnwhereas heifers on the fast growth path only had higher (P < 0.001) P8 fat thickness than those on the slow growth path.nAnimals on the fast growth treatment had higher (P < 0.001) levels of IMF% than the slow animals which were highern(P < 0.001) than the comp. growth treatment. AUS-MEAT and US marbling scores were not different among growth paths.nAnimals finished on the fast growth path had a lower (P < 0.001)RBY%than those on either the slow or comp. growth paths.nThe RBY-sired progeny had higher (P < 0.001) finishing liveweight and hot standard carcass weight than either RBY andnIMFor IMF-sired animals. IMF-sired progeny had higher (P<0.01) rib fat thickness than eitherRBYorRBY-and IMF-sirednanimals. There was also a similar trend for P8 fat thickness but the effects were not significant. The RBY-sired animals hadnlower AUS-MEAT marbling scores (P < 0.01), US marbling scores (P < 0.001) and levels of IMF% (P < 0.01) than either ofnthe other two sire treatments. RBY-sired animals also had higher (P < 0.001) estimatedRBY%than those from the IMF siresnwhile those by RBY and IMF sires were intermediate and not significantly different from either. Calving time had littleninfluence on most carcass characteristics. However,WCanimals tended to be fatter and have higher marbling scores thanACnanimals. The IMF% was higher (P < 0.01) in WC animals from RBY and IMF sires than in the corresponding AC animals.nHeifers had lighter slaughter liveweight, carcass weight, were fatter and had higher marbling scores than steers. Heifers alsonhad lower (P < 0.001) RBY% than the steers. Ossification scores for heifers were higher (P < 0.001) than for steers by ~30nunits in AC calves and by 20 units inWCcalves. The results of this experiment confirm the effectiveness of using sires withnhigh estimated breeding value for the required characteristics in producing the desired improvements in the progeny. Thenabsence of any interactions of sire type with growth path indicates that differences between sire types will be similarnregardless of environmental conditions. Animals raised on a faster growth path after weaning produce carcasses with more fatnand more IMF% than those grown on slower growth paths.