Energy requirements of Dorper crossbred ewe lambs1

The ME and NE requirements of Dor- per crossbred ewe lambs grown from 35 to 50 kg BW were assessed in a comparative slaughter trial. Thirty- five ewe lambs (33.5 ± 0.6 kg BW) of F 1 crosses of purebred Dorper and thin-tailed Han sheep were used: 7 lambs were slaughtered at the start of the trial to pro- vide baseline measures of body composition and 7 lambs were fed ad libitum and slaughtered when they reached 43 kg BW to provide intermediate measures of body composition. The remaining 21 lambs were divided into 3 groups of 7 lambs each and fed a pelleted mixed diet (concentrate:roughage = 44:56, DM basis) for ad libitum intake or 65 or 45% of ad libitum intake. All 3 groups were slaughtered when the ad libitum group reached 50 kg BW. Total body energy, N, fat, ash, and moisture content were measured. In a separate trial, 15 ewe lambs (39.5 ± 0.7 kg BW) of F 1 crosses of purebred Dorper and thin-tailed Han sheep were housed in metabolism cages to evaluate the ME value of the diet at each of the 3 lev- els of feed intake. In vivo methane production was mea- sured by open-circuit respirometry along with the collec- tion of all feces and urine. The daily NE m requirement of the ewe lambs was 280 kJ/kg metabolic BW (BW 0.75 ) or 292 kJ/kg metabolic shrunk BW (SBW 0.75 ), whereas the daily ME requirement for maintenance was 418 kJ/kg BW 0.75 or 437 kJ/kg SBW 0.75 , with a partial efficiency of ME utilization for maintenance of 0.67. The NE g require- ment ranged from 1.37 to 3.94 MJ/d for ADG from 100 to 250 g BW, and the partial efficiency of ME utilization for gain was 0.44. The NE and ME requirements of Dorper × thin-tailed Han crossbred ewe lambs were lower than the recommendations of the United States' nutritional system.