|Leeds, Timothy - Tim|
|Taylor, Joshua - Bret|
Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/3/2014
Publication Date: 3/18/2014
Publication URL: www.journalofanimalscience.org/content/92/5/1980.full?sid=057baf48-ba73-4f56-8efc-5d3e0762cf10
Citation: Notter, D.R., Mousel, M.R., Leeds, T.D., Zerby, H.N., Moeller, S.J., Lewis, G.S., Taylor, J.B. 2014. Evaluation of Columbia, USMARC-Composite, Suffolk, and Texel rams as terminal sires in an extensive rangeland production system: VI.Measurements of live-lamb and carcass shape and their relationship to carcass yield and value. Journal of Animal Science. 92(5):1980-1994. Interpretive Summary: Linear measurements on live animals and (or) carcasses may serve as indicators of carcass merit. This study characterized differences in live-animal and carcass shape among crossbred lambs. Associations of these measurements with carcass yield and value were investigated to identify potential prediction strategies. We found significant improvements in accuracy of prediction associated with measurements of carcass length, leg width, shoulder width, and cannon bone length. However, the additional accuracy achieved from use of such measurements was small, highlighting the challenges involved in development of fully automated systems to assess carcass value and the need to consider other sources of information such as ultrasound measurements in live animals, direct measurements of muscling and fatness in ribbed carcasses, and live-animal X-ray computed tomography.
Technical Abstract: Linear measurements on live lambs and carcasses can be used to characterize sheep breeds and may have value for prediction of carcass yield and value. This study used 512 crossbred lambs produced over 3 yr by mating Columbia, USMARC Composite, Suffolk, and Texel rams to adult Rambouillet ewes to assess sire-breed differences in live-animal and carcass shape and to evaluate the value of shape measurements as predictors of chilled carcass weight (CCW); weights of high-value cuts (rack, loin, leg, and sirloin) before (HVW) and after (TrHVW) trimming and deboning of the leg and sirloin; and estimated carcass value before (CVal) and after trimming of high-value cuts (TrCVal). Lambs were produced under extensive rangeland conditions, weaned at an average age of 132 d, fed a concentrate diet in a drylot, and harvested in each year in 3 groups at target mean BW of 54, 61, and 68 kg. Canonical discriminant analysis indicated that over 93% of variation among sire breeds was accounted for by the contrast between tall, long, lightly muscled, and somewhat heavier breeds (i.e., the Columbia and Suffolk) compared with shorter, more thickly muscled, and somewhat lighter breeds. After correcting for effects of year, harvest group, sire breed, and shipping BW, linear measurements on live lambs contributed little to prediction of CCW. Similarly, after accounting for effects of CCW, linear measurements on live animals further reduced residual SD (RSD) of dependent variables by 0.2 to 5.7%, with generally positive effects of increasing live leg width and generally negative effects of increasing heart girth. Carcass measurements were somewhat more valuable as predictors of carcass merit. After fitting effects of CCW, additional consideration of carcass shape reduced RSD by 2.1, 3.6, 9.5, and 2.2% for HVW, TrHVW, CVal, and TrCVal, respectively. Effects of increasing carcass leg width were positive for HVW, TrHVW, and TrCVal. We also observed positive effects of increasing carcass length on TrCVal, and negative effects of increasing cannon bone length on HVW and CVal. Increasing shoulder width had positive effects on CVal but negative effects on TrHVW. Differences in lamb and carcass shape were significantly associated with carcass yield and value, but the additional accuracy associated with use of these measurements was modest relative to that achieved from use of only shipping BW or CCW.