Effects of pre-weaning castration and age at slaughter on growth performance and carcass characteristics of Crossbred Dorper lambs (Ovis aries, Linnaeus, 1758)

Abstract

The experiment was conducted on 20 post-weaned, male Crossbred Dorper lambs (Ovis aries, Linnaeus, 1758). Castration was performed before weaning using the rubber ring method, nine (9) weeks prior to the start of the experiment. Age at the beginning of the trial for all lambs was 12 weeks and average live weights were 17.7 kg (castrated) and 16.9 kg (intact). Following the grow-out period, lambs were slaughtered at 6 and 8 months old. Carcass quality traits measured were, carcass weight, dressing percentage, loin eye area, internal organ mass, mesenteric fat deposits and the mass of offal. There was no significant difference in initial live weight between the castrated and intact lambs (P > 0.05). Average daily weight gain, at week 7 of the trial, was significantly higher for intact lambs (P < 0.05). Final live weight however, was not significantly affected by castration (P > 0.05). Slaughter time and castration also significantly impacted carcass quality traits such as loin eye muscle area and rack, shoulder and leg weights. Initial body weight was significantly correlated (P < 0.05) with final live weight (r= 0.53), empty body weight (r =0.53) and hot carcass weight (r =0.56). Final live weight and fasted body weight were significantly higher for intact animals slaughtered at 8 months (P < 0.05). Carcass weight was significantly higher for animals slaughtered at 8 months (P < 0.05), compared to those slaughtered at 6 months. However, no significant difference in carcass weight was observed for castrated and intact lambs (P > 0.05) slaughtered at 6 and 8 months respectively. Carcass analysis revealed significantly heavier lungs and gastro-intestinal tracts in animals slaughtered at 8 months (P < 0.05). The weight of head, skin and feet were significantly larger for intact animals slaughtered at 8 months (P < 0.05). Intraperitoneal fat deposits as well as liver and kidney organ mass did not vary significantly between intact and castrated subjects (P>0.05). Skin and head weights were significantly larger (P<0.05) for intact males slaughtered at 8 months. The study revealed that pre-weaning castration negatively impacted growth performance as well as the carcass traits in Crossbred Dorper lambs. The combination of intact animals slaughtered at 8 months proved to be most favorable based on growth and carcass quality traits that were measured. Hence further investigations into optimal castration age and slaughtering time are required to maximize output from Crossbred Dorper lambs grown in Jamaica.