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This study aimed to investigate the net and metabolizable energy (NE and ME) requirements of Dorper crossbred lambs. Thirty-five Dorper×thin-tailed Han crossbred intact male lambs weaned at approximately 50 d of age (20.26±1.29 kg of BW), were used. Seven randomly selected lambs were slaughtered at the start of the trial (baseline group). An intermediate group consisting of 7 randomly selected lambs fed for ad libitum intake was slaughtered when the lambs reached an average BW of 28.2 kg. The remaining 21 lambs were alloted randomly to 3 levels of dry matter intake: ad libitum, or restricted to 70 or 40% of the ad libitum intake. All the lambs were slaughtered when the ad libitum fed sheep reached 35 kg of BW. Total body energy, crude protein, fat, ash, and moisture contents were determined. In a digestibility trial, fifteen Dorper×thin-tailed Han crossbred intact male lambs (32.38±2.23 kg of BW) were housed in metabolism cages and used in a completely randomized design experiment to evaluate the ME value of the diet at 3 feed intake levels. The results showed that the maintenance requirements for NE and ME were 250.61 and 374.21 kJ/kg metabolic shrunk body weight (SBW0.75), respectively. The partial efficiency of energy use for maintenance was 0.67. Net energy requirements for growth ranged from 1.12 to 5.31 MJ/d, for the lambs gaining 100 to 350 g/d from 20 to 35 kg BW. Partial efficiency of ME for growth was 0.42. In conclusion, the current study suggested that the NE requirement for maintenance and growth of Dorper×thin-tailed Han early-weaned crossbred lambs were lower than those reported by existing AFRC and NRC nutritional systems.

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.

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.