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A 3-yr study was conducted to com-prehensively evaluate Columbia, Suffolk, USMARC-Composite (Composite), and Texel breeds as terminal sires in an extensive rangeland production system. The objective was to estimate breed-of-ram effects on ewe fertility, prolificacy, and dystocia, and sire breed effects on lamb survival and growth until weaning at approxi-mately 132 d of age. Data were from 22 Columbia, 22 Composite, 21 Suffolk, and 17 Texel rams with 957 exposures to 574 adult Rambouillet ewes (3- to 7-yr-old at lambing), 908 lambings, and 1,834 lambs. Ram breed did not affect ewe fertility (mean = 94.9%; P = 0.73), total number born per ewe lambing (mean = 2.02 lambs; P = 0.20), number born alive per ewe lamb-ing (mean = 1.90 lambs; P = 0.24), or number weaned per ewe lambing (mean = 1.45 lambs, P = 0.94). Dys-tocia rates were different (P = 0.01) for ewes mated to Columbia (12.2%), Composite (13.5%), Suffolk (25.7%), and Texel rams (31.9%) during I yr of the study, but differences among ram breeds were not repeatable (P > 0.38) during the other 2 yr. Suffolk-sired lambs were heavier (P < 0.02) at birth (5.5 kg) and weaning (40.3 kg) than lambs sired by the other breeds, which did not differ (P > 0.34) for birth weight (mean = 5.3 kg). Texel-sired lambs (37.4 kg) were lighter (P < 0.02) at weaning than Columbia- (38.8 kg) and Composite-sired (38.4 kg) lambs, which did not differ (P = 0.40) for weaning weight. Sire breed effect approached significance (P = 0.06) for lamb survival to weaning; estimated survival probabilities were 0.87 (Columbia), 0.89 (Composite), 0.93 (Suf-folk), and 0.86 (Texel) for lambs reared by their birth dam. Interaction between sire breeds and birth weight affected (P < 0.001) lamb survival and revealed that lightweight Columbia- and Suffolk-sired lambs had a greater risk of death than lightweight lambs sired by Composite and Texel rams, but risk of death did not increase substantially for heavyweight lambs from any of the breeds. When mated to adult Rambouillet ewes in an extensive rangeland production system, the use of Suffolk rams is warranted to improve preweaning growth of market lambs and is not predicted to affect ewe fertility, ewe prolificacy, dystocia, or lamb surviv-al compared with the other sire breeds we tested. [ABSTRACT FROM AUTHOR]

Over 3 yr, postweaning growth patterns and changes in ultrasonic measurements of fat depth (FD) and LM area were assessed for 1,049 crossbred ewe and weather lambs (Ovis aries) produced by mating adult Rambouillet ewes to 1 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 16 wk, and scanned using ultrasound at 2-wk intervals to estimate FD and LM area between the 12th and 13th ribs. Lambs sired by Suffolk rams were 5 to 12% heavier (P < 0.05) at start of test, grew 14 to 22% faster (P < 0.001), and were correspondingly 7 to 14% heavier (P < 0.001) after 90 d on test than lambs sired by rams of the other 3 breeds. At this time, lambs sired by Texel rams were 5% lighter (P < 0.01) than Columbia- or Composite-sired lambs, which did not differ (P > 0.20). Columbia-sired lambs had less FD (8.9 mm) but smaller LM areas (15.6 cm2) at 90 d on test (both P< 0.01) than lambs sired by rams of the other breeds (average of 9.8 mm for FD and 16.6 cm2 for LM area), which did not differ for either measurement at this time. At 60 kg, predicted FD differed among sire breeds (P < 0.001) and were similar for Suffolk- (7.6 mm) and Columbia-sired (7.9 mm) lambs, intemiediate for Composite-sired lambs (9.1 mm), and largest for Texel-sired (10.1 mm) lambs. At a BW of 60 kg, LM area differed between all pairs of sire breeds (P < 0.05), and was largest for Texel-sired lambs (16.7 cm2), followed by Composite-, Suffolk-, and Columbia-sired lambs (15.7, 14.8, and 14.5 cm2, respectively). At a predicted FD of 9.1 mm (the boundary between U.S. Yield Grades 3 and 4), the predicted LM area for Suffolk-sired lambs (16.2 cm2) was similar (P >0.10) to that of Texel-sired lambs (16.0 cm2) and superior (P < 0.01) to that of Composite- (15.7 cm2) and Columbia-sired lambs (15.4 cm2). Lambs sired by Suffolk rams were thus equal or superior to lambs sired by the other 3 breeds in growth, FD, and LM area at comparable ages, fatness at 60 kg, and LM area at a FD of 9.1 mm, but inferior in LM area to Texel- and Composite-sired lambs at comparable BW. [ABSTRACT FROM AUTHOR]

To evaluate terminal-sire breeds, harvest BW, prefabrication carcass measurements, and organ weights were evaluated over 3 yr for 518 crossbred weather lambs (Ovis aries). Lambs were produced by single-sire matings of 22 Columbia, 22 USMARC-Composite (Composite), 21 Suffolk, and 17 Texel rams to adult Rambouillet ewes. Lambs were raised to weaning under an extensive western rangeland production system and finished in a feedlot on a high-energy finishing diet. Wethers were randomly assigned to be harvested at an average BW of 54.4, 61.2, or 68.0 kg and then transported to The Ohio State University abattoir for harvest. Wether BW was recorded before transport (off-test BW) and before harvest. Prefabrication carcass measurements and organ weights were recorded either after harvest or after an approximate 24-h chill. At comparable numbers of days on feed, Suffolk-sired lambs had heavier (P < 0.01) off-test BW, harvest BW, HCW, chilled carcass weight (CCW), and kidney weights than lambs sired by the other breeds. Suffolk-sired lambs had more (P < 0.01) kidney-pelvic fat than did Columbia-sired lambs; Composite- and Texel-sired lambs were intermediate and did not differ (P > 0.06) from the other crossbred lambs. Texel- and Suffolk-sired lambs had larger LM area and greater conformation scores than Columbia-sired lambs (P < 0.03). Texel-sired lambs had greater (P < 0.01) body wall thickness, quality grades, and leg scores than Columbia-sired lambs. Composite-and Suffolk-sired lambs did not differ from each other or from lambs sired by any other breed for body wall thickness (P > 0.18) and were intermediate for quality grades and leg scores. Sire breed did not affect (P > 0.05) shipping shrink, dressing percentage, pelt weight, liver weight, and fat depth. Adjusting data to a comparable off-test BW or CCW modified sire breed rankings for some measurements. Texel-sired lambs were equal or superior to lambs sired by other breeds for HCW, CCW, dressing percentage, pelt weight, LM area, quality grade, and leg and conformation scores. However, Texel-sired lambs also had values for kidney-pelvic fat weight, fat depth, and body wall thickness that were equal to or greater than those of lambs sired by the other breeds, indicating increased fatness at comparable BW. Producers can use these results to select terminal-sire sheep breeds that will complement their production system and improve market lamb value. [ABSTRACT FROM AUTHOR]