PSIX-15 Performance, and carcass, and retail cuts yield of genetically improved lambs weaned and slaughtered at two body weights and fed total rations during the growing and finishing periods.

Abstract The use of genetically improved lambs, and management and nutritional strategies to enhance performance and carcass characteristics, has become critical for increasing sheep production in tropical regions. Likewise, information on the optimal weaning and slaughter body weight for maximizing lamb production is needed. This experiment evaluated daily growth, carcass, and retail cuts yield of genetically improved lambs fed total rations (TR) from weaning to slaughter at two body weights. The research was conducted at the University of Puerto Rico Small Ruminant Project. Eight crossbred lambs (Dorset-Ile de France ram × Criollo ewe) were used as experimental units. Lambs were weaned (W) and slaughtered (S) at two body weights (lighter lambs, LL, W = 14.5 kg and S = 35.0 kg and heavier lambs, HL, W = 20.5 kg and S = 46.0 k). Lambs were fed a TR containing 60% concentrate (14% CP) and 40% grass hay, offered at 4% of body weight during the feeding period. Weekly body weight measurements were taken to calculate daily gain from weaning to slaughter as a criterion to determine lamb productive performance. At slaughter, hot carcass yield (HCY), cold carcass yield (CCY), and retail cuts’ whole weight and yields relative to cold carcass weight were determined in three lambs per treatment. Retail cuts included neck (NC), ribs (RB), loin (L), shoulder (SL), French chops (FC), shanks (SH), and back leg (BL). Data were analyzed using a completely randomized design with two treatments and four and three repetitions for performance and carcass characteristics, respectively. Days on feed to reach slaughter weight were 124 and 168 for LL and HL, respectively. The average daily gain was higher (P< 0.05) for LL than HL (172.3 vs. 155.8 g/d). HCY (LL = 39.32%, HL = 39.30%) and CCY (LL = 38.58%, HL = 38.44%) were similar for both groups. As expected, retail cut weights were higher (P< 0.05) in HL than in LL. The yield of NC (4.09% vs 3.69%) and SH (7.56% and 6.96%) relative to cold carcass weight was higher (P< 0.05) in LL than HL, but SL (25.09% and 25.77%), FC (10.99% and 11.52%), and BL (28.5%1 vs 27.19%) were similar. The HL had higher (P< 0.05) RB (8.21% vs 7.55%) and L (14.42% vs 12.94%) yield than LL. In conclusion, weaning and slaughtering body weight significantly affects productive and carcass characteristics of genetically improved lambs that fed total rations during the growing and finishing periods.