Requirements of metabolizable protein by Dorper × thin-tailed Han crossbred ewe lambs

The requirement of net protein (NP) and metabolizable protein (MP) by Dorper crossbred ewe lambs grown from 35 to 50 kg of body weight (BW) was assessed by comparative slaughter experiment. Thirty-five ewe lambs (33.5 ± 0.6 kg BW) of F₁ crosses of Dorper × thin-tailed Han sheep were used: 7 lambs were slaughtered as reference animals at the start of the trial, and the remaining 28 lambs were randomly divided into 4 groups of 7 lambs each. Three of the 4 groups were fed a pelleted mixed diet (concentrate/roughage = 44:56, dry matter basis) for ad libitum intake or 65% or 45% of ad libitum intake, and they were all slaughtered when the lambs that were fed ad libitum reached 50 kg BW. The lambs from the fourth group were also fed ad libitum and slaughtered at 43 kg BW as the intermediate group. The intake of MP by the animals of these 4 groups was estimated, and their total body protein and protein retention were measured. The daily requirements of NP and MP for maintenance were 1.52 and 3.98 g/kg BW^0.75 , respectively, with a partial efficiency of MP utilization for maintenance of 0.38. The MP requirement for growth ranged from 77.4 to 124.5 g/day for average daily gains from 100 to 250 g BW, and the partial efficiency of MP utilization for growth was 0.66. The Dorper crossbred ewe lambs required more MP for both maintenance and growth in comparison with the recommendations of the US nutritional system.