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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 BW0.75 , 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.

Comparative slaughter trials were conducted to determine the net zinc (Zn) requirements for Dorper crossbred ram lambs and ewe lambs. Thirty-five Dorper×thin-tailed Han crossbred lambs [20 kg body weight (BW)] of each gender were subjected to the same slaughter procedures: seven lambs were randomly chosen and slaughtered at 20 kg BW as the baseline group for measuring the initial body composition; another seven lambs were also randomly chosen and offered a pelleted mixed diet for ad libitum intake and slaughtered at 28 kg BW; the remaining 21 sheep were randomly divided into three groups containing seven sheep each and subjected to the same diet either ad libitum or at 70% or 40% of ad libitum intake. The three groups were slaughtered when the sheep fed ad libitum reached 35 kg of BW. Finally, the body Zn contents were determined. The net Zn requirements for maintenance were 97 and 165 μg/kg BW for Dorper×thin-tailed Han crossbred ram lambs and ewe lambs, respectively, and the requirements for growth decreased from 23.4 to 23.2 mg/kg BW gain for ram lambs and from 23.8 to 22.1 mg/kg BW gain for ewe lambs as their BW increased from 20 to 35 kg. These findings were similar to those reported by most nutritional systems, except that the maintenance requirements for ewe lambs were greater than the previously published values.

A comparative slaughter trial was conducted to estimate the phosphorus (P) requirement for maintenance and growth of crossbred lambs of Dorper with a Chinese indigenous sheep breed, thin-tailed Han sheep. Thirty-five Dorper×thin-tailed Han crossbred, noncastrated ram lambs (20.3±0.22 kg of shrunk body weight (SBW)) were used. Seven lambs were randomly chosen and slaughtered at 20 kg SBW as the baseline group for measuring initial body composition. Another seven lambs were also randomly chosen and offered a pelleted mixed diet for ad libitum intake and slaughtered at 28 kg SBW. The remaining 21 sheep were randomly divided into 3 groups with 7 sheep each and subject to the same diet of either 70 or 40% of ad libitum intake. The 3 groups were slaughtered when the sheep fed ad libitum reached 35 kg of SBW. Body P contents were determined after slaughter. The results showed that the net P requirement for maintenance was 30.0 mg/kg of empty body weight (EBW) or 23.4 mg/kg body weight (BW), and the P requirement for growth decreased from 5.3 to 5.0 g/kg of EBW gain as the lamb grew from 20 to 35 kg. The net P requirement for growth of Dorper×thin-tailed Han crossbred ram lambs was lower than that of sheep adopted by the American nutritional system.

This study aimed to determine the energy requirements of Dorper crossbred sheep that have been used for meat production in China. Thirty-five 1/2 Dorper×1/2 thin-tailed Han crossbred noncastrated ram lambs [34.1±0.6 kg body weight (BW)] were used in a comparative slaughter trial. Seven ram lambs were randomly selected as the baseline group and slaughtered at 35 kg BW. The remaining 28 lambs were randomly divided into four groups of seven lambs each. Three of the four groups were fed a mixed diet either for ad libitum intake, 60% or 45% of the ad libitum intake. The three groups were slaughtered when the ram lambs that were fed ad libitum reached 50 kg BW. The ram lambs from the fourth group were also fed ad libitum as an intermediate group and slaughtered at 43 kg BW. Total body energy, nitrogen, fat, ash, and moisture content were measured. In a digestibility trial, another 15 ram lambs (41.3±0.8 kg BW) were housed in metabolism cages to estimate the metabolizable energy (ME) value of the diet at the three levels of feed intake. The daily net energy (NE) requirement for maintenance was 263 kJ/kg 0.75 of BW or 278 kJ/kg 0.75 of shrunk BW (SBW), with a partial efficiency of ME utilization for maintenance of 0.69. The NE requirement for growth ranged from 1.12 to 5.31 MJ/d for daily gains of 100–400 g BW, or from 1.29 to 6.18 MJ/d for daily gains of 100–400 g SBW. The partial efficiency of ME utilization for growth was 0.46. The energy requirements of Dorper×thin-tailed Han crossbred ram lambs were lower than those recommended by the British or American nutritional systems.