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Title:   Author  item
                                            NOTTER, DAVID - Virginia Polytechnic Institution & State Universityitem
                                            Leeds, Timothy

                                                         - *Tim*item
                                            Mousel, Michelleitem
                                            Taylor, Joshua

                                                         - *Bret*item
                                            Kirschten, Daviditem
                                            Lewis, Gregory
  Submitted to: Journal of Animal Science
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 2/13/2013
                                    Publication  Date: 3/9/2012
                                    Citation: Notter, D.R., Leeds, T.D., Mousel, M.R., Taylor, J.B., Kirschten, D.P., Lewis, G.S. 2012. Evaluation of Columbia, USMARC-Composite, Suffolk, and Texel rams as terminal sires in an extensive rangeland production system:  II. Postweaning growth and ultrasonic measures of composition.. Journal of Animal Science. 90:2941-2952..Interpretive Summary: A large percentage of the market lambs in the U.S. are born and reared to weaning in extensive Western rangeland production systems.  After weaning, the lambs are commonly moved to feed yards and fed high-energy diets until they are harvested for human foods.  The efficiency of growth from weaning to harvest, and carcass merit and value, are important determinants of profitability. Loin muscle area and depth of fat over the loin muscle are reliable predictors of carcass merit.  Thus, USDA, Agricultural Research Service and Virginia Tech scientists conducted a multiyear study to determine the effects of sire breed on the performance of crossbred lambs that were produced under extensive Western rangeland conditions.  Rams of the Columbia, USMARC Composite (Composite), Suffolk, and Texel breeds were mated with Rambouillet ewes to produce the lambs for this study.  Results from the study indicate that Suffolk-sired lambs were heavier at weaning and grew faster after weaning than did Composite-, Columbia-, or Texel-sired lambs.  At comparable body weights, Suffolk- and Columbia-sired lambs had less fat over the loin muscle than did Texel- and Composite-sired lambs, but Composite- and Texel-sired lambs had greater loin muscle areas, which are an indicator of overall muscling, than did Suffolk- and Columbia-sired lambs.  However, at similar fat depths, loin muscle area of Suffolk-sired lambs was greater than that of  Composite-, Columbia-, and Texel-sired lambs.  We concluded that a substantial premium would be required for larger loin muscle area to compensate for slower growth and greater fatness at comparable body weights in Composite- and Texel-sired lambs.  Sheep producers can use the data from this study to select sire breeds that are consistent with their production and marketing objectives.
                                Technical Abstract: Over 3 yr, postweaning growth patterns and changes in ultrasonic measurements of fat depth and loin muscle area were assessed for 1,049 crossbred ewe and wether lambs produced by mating adult Rambouillet ewes to one of 22 Columbia, 22 USMARC-Composite (Composite), 21 Suffolk, or 17 Texel rams and raised to weaning under extensive Western rangeland conditions.  After weaning, lambs were transitioned to a high-energy finishing diet in a feedlot, weighed weekly for 13 to 17 wk, and scanned using ultrasound at 2-wk intervals to estimate fat depth and loin muscle area between the 12th and 13th ribs.  Lambs sired by Suffolk rams were 5 to 12% heavier at start of test, grew 14 to 22% faster, and were correspondingly 7 to 14% heavier at 90 d than lambs sired by rams of the other 3 breeds.  At 90 d, Texel-sired lambs were 5% lighter than Columbia- or Composite-sired lambs, which did not differ.  Columbia-sired lambs had less fat depth (8.9 mm) but smaller loin muscle areas (15.6 cm2) at 90 d on test compared with lambs sired by rams of the other breeds (average of 9.8 mm for fat depth and 16.6 cm2 for loin muscle area), which did not differ for either measurement at this time.  At 60 kg, predicted fat depths were similar for Suffolk- (7.6 mm) and Columbia-sired (7.9 mm) lambs, intermediate for Composite-sired lambs (9.1 mm), and largest for Texel-sired (10.1 mm) lambs.  Loin muscle areas differed between all pairs of sire breeds at 60 kg, and was largest for Texel-sired lambs (16.7 cm2), followed by Composite-, Suffolk-, and Columbia-sired lambs at 15.7, 14.8, and 14.5 cm2, respectively.  Lambs sired by Suffolk rams were thus equal or superior to lambs sired by the other 3 breeds in growth, fat depth, and loin muscle area at comparable ages, fatness at 60 kg, and loin muscle area at a fat depth of 9.1 mm (the boundary between U.S. Yield Grades 3 and 4), but inferior in loin muscle area to Texel- and Composite-sired lambs at comparable BW.


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