Effect of tail docking in Awassi lambs on metabolizable energy requirements and chemical composition of carcasses

Abstract

AbstractThe effect of tail docking on metabolizable energy requirements and carcass characteristics was studied using 80 weaned entire Awassi male lambs. Docking was performed within 3 days of birth and lambs were weaned at 90 days old. Docked and undocked lambs were randomly allocated to four groups, individually penned and offered different amounts of a pelleted concentrate diet. The pelleted diet was estimated to contain 11·8 MJ of metabolizable energy (ME) and 182 g of crude protein (CP) per kg dry matter (DM). Lambs on the high levels of intake were slaughtered at a target weight of approximately 45 kg. Other lambs were maintained on the diet for 149 days before being slaughtered. The right sides of all carcasses were cut into standardized commercial cuts then dissected into muscle, fat and bone. The soft tissue was pooled and analysed for DM, C P, ash and fat. Prediction of live-weight gain (LWG) and empty body gain for a given ME intake (MEI) was made using the growth and MEI data. MEI was expressed as MJ per kg metabolic body weight (M 0·75) per day. Tail docking had no effect (P > 0·05) on lamb growth from birth to weaning. During the post-weaning growth period, LWG and empty body gain were significantly higher (P < 0·05) for undocked lambs than docked lambs, at feeding levels between 0·31 and 0·52 MJ/kg M 0·75 per day and similar (P > 0·05) at high levels of intakes (between 0·74 and 1·1 MJ/ kg M 0·75 per day). Hot and cold carcass weights were similar (P > 0·05) for the two groups. Differences in empty body weight and fleece-free empty body weight were significant (P < 0·05) only for the 0·443 to 0·522 MJ/kg M 0·75 per day level of ME intake. Predicted ME requirements were higher for docked lambs for an estimated LWG between 0 and 100 g/day and lower for higher LWG (125 to 225 g/day). Docking had no effect (P > 0·05) on food conversion efficiency (FCE). Carcasses from docked lambs had significantly lower (P < 0·001) internal plus tail fat. Pooled soft tissue excluding tail fat, for the undocked lambs contained significantly more (P < 0·01) protein, less (P < 0·001) fat, higher (P < 0·01) moisture and similar (P > 0·05) ash content.