|Van Vleck, Lloyd|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2005
Publication Date: 1/3/2005
Citation: Rios-Utrera, A., Cundiff, L.V., Gregory, K.E., Koch, R.M., Dikeman, M.E., Koohmaraie, M., Van Vleck, L.D. 2006. Effects of age, weight and fat slaughter end points on estimates of breed and retained heterosis effects for carcass traits. Journal of Animal Science 84:63-87. Interpretive Summary: Comparison of beef breeds for carcass traits usually is at a common end point such as a specified slaughter age. Other end points might be a specified level of fat thickness at the 13th rib or level of slaughter weight. This study of 14 carcass traits of 1,664 purebred (9) and composite breed (3) steers showed that rankings of breed groups for some traits may depend on the end point and level of end point used. Estimates of retained heterosis for composite breeds may also depend on the end point and level of the end point. In general important differences in carcass traits were found among the breed groups. Exploitation of breed groups for optimal income from beef production will require attention to different slaughter end points and how they interact with the production system and marketing situation. The specific results for steers in this analysis may not apply to marketing of heifers and bulls or hormonally implanted steers due to potential differences in the carcass traits relative to carcass traits for non implanted steers such as used in this study.
Technical Abstract: The influence of different levels of fat thickness (AFT) and hot carcass weight (HCW) slaughter end points (covariates) on estimates of breed and retained heterosis effects was studied for 14 carcass traits from 1,664 purebred and composite steers, serially slaughtered, from the Germ Plasm Utilization Project at the U.S. Meat Animal Research Center (MARC). Linear contrasts among breed solutions were estimated at 0.7, 1.1 and 1.5 cm of AFT, and at 295.1, 340.5 and 385.9 kg of HCW. For constant slaughter age, linear contrasts were adjusted to the overall mean (432.5 d). Estimates of (co)variances for animal models were obtained by REML. Breed effects for Red Poll, Hereford, Limousin, Braunvieh, Pinzgauer, Gelbvieh, Simmental, Charolais, MARC I, MARC II, and MARC III were estimated as a deviation from Angus. In addition, purebreds were pooled in three categories based on lean-to-fat ratio and then differences were estimated among groups. Retention of combined individual and maternal heterosis was estimated for each composite (F3 generation). Mean retained heterosis for the three composites was also estimated. Breed rankings and expression of heterosis varied within and among slaughter end points. For example, Charolais had greater (P < 0.05) dressing percentages than Angus at the two largest levels of AFT, smaller (P < 0.01) percentages at the two largest levels of HCW, whereas the two breeds did not differ (P ' 0.05) at a constant age. The MARC III composite produced 9.7 kg more (P < 0.01) fat than Angus at AFT of 0.7 cm, but 7.9 kg less (P < 0.05) at AFT of 1.5 cm. For MARC III, estimate of retained heterosis for HCW was significant (P < 0.05) at the lowest level of AFT, but at the intermediate and at the highest levels, estimates were nil. The pattern was the same for MARC I and MARC III for LM area. Adjustment for age resulted in near zero estimates of retained heterosis for AFT and, similarly, adjustment for HCW resulted in nil estimates of retained heterosis for LM area. For actual retail product as a percentage of HCW, the estimate of retained heterosis for MARC III was significantly (P < 0.05) negative (-1.27%) at 0.7 cm, but was significantly (P < 0.05) positive (2.55%) at 1.5 cm of AFT. Furthermore, for MARC III, estimates of heterosis for some traits (fat as a percentage of HCW as another example) also doubled in magnitude depending on different levels of AFT end point.