1University of Maryland Eastern Shore, Princess Anne, MD
2Maryland Cooperative Extension, College Park, MD
3WMREC, Keedysville, MD

At weaning, 43 Suffolk-(SK), Texel-(TK), and Dorper-(DK) sired Katahdin crossbred lambs were randomly removed from pasture and placed in a feedlot (GF), while 125 TK, SK, and DK lambs remained on pasture (PF) to determine the effects of feeding regime on carcass traits. At an average BCS of 2.8 (1-5 scale with 1=emaciated and 5=obese), 5 lambs/breed from both GF (134 ± 1.2d of age) and PF (153 ± 1.5d of age) were slaughtered to collect carcass data. The PF lambs had greater (P < 0.05) transport BW loss (-1.9 vs -1.0 ± 0.1 kg) and greater (P < 0.01) empty digestive tract weight (EDT; 5.3 vs 3. 6± 0.1kg), dressing percentage (50.7 vs 46.7 ± 0.7%), LEA (17.9 vs 16.0 ± 0.5 cm², leg circumference (85.5 vs 77.5 ± 1.4cm), carcass length (103 vs 98.2 ± 0.8cm) and retail cut weights (14.5 vs 13.2 ± 0.3 kg) compared to GF lambs. DK lambs had the lowest (P < 0.01) pluck and retail weights (1.8 ± 0.1 and 13.1 ± 0.3kg, respectively) when compared to SK (2.1 ± 0.1 and 14.2 ± 0.3 kg, respectively) and TK (2.0 ± 0.1 and 14.3 ± 0.3kg, respectively) lambs. EDT, hot and cold carcass weights were lower (P < 0.05) in DK lambs (4.3 ± 0.1, 19.0 ± 0.5, and 18.7 ± 0.4 kg, respectively) than SK lambs (4.8 ± 0.1, 20.8 ± 0.5, and 20.3 ± 0.4kg, respectively) while TK lambs (4.4 ± 0.1, 20.3 ± 0.5, and 19.9 ± 0.4 kg, respectively) were intermediate. SK lambs had longer (P < 0.05; 107 ± 0.8cm) carcasses than TK (97.8 ± 0.8cm) and DK (97.1 ± 0.8cm) lambs. DK lambs (3.6 ± 0.3 mm) had greater (P < 0.05) back fat than TK lambs (2.4 ± 0.3 mm) while SK lambs (3.0 ± 0.3 mm) were intermediate. LEA was largest (P < 0.01) in TK (18.3 ± 0.65 cm²) lambs compared to both DK (16.3 ± 0.65 cm²) and SK lambs (16.4 ± 0.65 cm²). In addition, the carcasses from TK lambs received the highest (P < 0.05) quality grades and CIE L* and hue angle values and SK lambs had the highest (P < 0.05) mechanical shear force values. Overall, PF lambs had more muscle mass than their GF counterparts when slaughtered at a similar BCS, and sire breed had differential effects on carcass traits.