PSX-25 Performance, carcass, wholesale, and retail cuts yield of genetically improved entire or castrated crossbred lambs fed total rations under heat stress conditions

Abstract Lamb production in tropical areas is generally conducted with native animals in extensive grazing conditions on naturalized pastures under heat stress. Strategies to enhance productivity using genetically improved intact or castrated crossbred lambs fed with total ratios (TR) need to be evaluated. The performance of intact Dorset-Criollo (n = 10, EDSC, 20.48 kg), intact Dorper-Criollo (n = 8, EDPC, 20.58 kg) and castrated Dorper-Criollo (n = 4, CDPC, 18.40 kg) lambs fed a TR during the growing-finishing phase was evaluated. The TR contained 70% concentrate and 30% grass hay and was fed at 4% of lamb body weight (DMB) until slaughter (SBW, 38 to 40kg). During the trial lambs dry matter intake was recorded daily while weekly weights were taken to determine days on feed (DOF) to reach SBW, average daily gain (ADG) and feed conversion (FC). At slaughter, yields of hot (HCY) and cold (CCY) carcass, wholesale cuts (WSC) including neck (N), shoulder (SL), ribs 5-12 (RIBS), loin (LN) and leg (LG), and retail cuts (RTC) including shoulder chops (SCH), French chops (FCH), ribs (RS), back leg (BL) and shanks (SH) of lambs were determined. The WSC and RTC yield were determined as percentage of cold carcass weight. Performance data were analyzed as a randomized experimental (CRD) design over time. Carcass and cut yields data were analyzed as a CRD. LS-means were using for mean separation. Days on feed to reach SBW was less (P < 0.05) in EDSC (107 d) and EDPC (102 d) than CDPC (123 d). The ADG was greater (P < 0.05) in EDSC (215.0 g) and EDPC (189.0 g) than CDPC (167.6 g), but FC was similar (EDSC = 5.2, EDPC = 5.8, CDPC = 6.0). HCY and CCY were similar for EDSC (44.2% and 41.7%), EDPC (45.5% and 43.2%) and CDPC (46.1% and 43.2%). For WSC, N yield was greater (P < 0.05) in EDSC (4.3%) than EDPC (3.8%) and CDPC (3.5%), but RIBS was less (18.9% vs 20.9% and 20.9%, respectively). Yields of SL, LN, and LG were similar for EDSC (31.9%, 12.5% and 33.5%), EDPC (30.7%, 12.2% and 33.9%) and CDPC (31.1%, 13.0% and 33.9%). For RTC, the yield of SCH was greater (P < 0.05) in CDPC (26.6%) than EDPC (24.4%), but similar to EDSC (25.9%). FCH was less (P < 0.05) in EDSP (11.8%) than EDPC (14.4%) and CDPC (15.2%). No differences in RS (EDSC 6.5%, EDPC 6.3%, CDPC 5.5%), BL (EDSC 28.9%, EDPC 29.2%, CDPC 29.0%), and SH (EDSC 7.0%, EDPC 7.3%, CDPC 7.4%) were detected. In summary, castration decreases performance of genetically improved lambs as evidenced by longer DOF to reach SBW and lower ADG than intact animals, but did not influence carcass yield. Differences in WSC and RTC yield were observed among genetic groups and animal type.