Energy Requirements for Maintenance and Growth of German Mutton Merino Crossbred Lambs

A comparative slaughter trial and a metabolism trial were conducted to determine the requirement of net energy (NE) and metabolizable energy (ME) by the crossbreed of German Mutton Merino×Inner Mongolia Merino for fattening from 35 to 50 kg of body weight (BW). 49 crossbred female lambs ((33.9±2.3) (SD) kg BW) of German Mutton Merino×Inner Mongolia Merino were used. 34 lambs were randomly chosen for comparative slaughter, which were offered an identical mixture diet (concentrate:roughage=55:45) at 100, 75 or 55% of ad libitum intake, whereas the remainders were used in the metabolism trial to evaluate the ME of the diet after methane production was measured by open-circuit respirometry. As feed intake decreased from 100 to 75 and 55% of ad libitum intake, the apparent digestibility of dry matter (DM) linearly increased ( P =0.010) from 60.8 to 63.6 and 66.9%, respectively, and methane production decreased from 52.1 to 44.3 and 39.9 L d −1 , respectively, but the ratio of methane energy to gross energy intake increased linearly ( P =0.010) from 8.20 to 8.96 and 10.97%, respectively. Consequently, the ME values of the diet increased from 9.35 to 9.64 and 9.85 MJ kg −1 DM, respectively. The NE requirement for maintenance (NE m ) was 255 kJ kg −1 BW 0.75 , and the ME requirement for maintenance (ME m ) was 352 kJ kg −1 BW 0.75 , with a partial energy efficiency for maintenance (k m ) of 0.72. The NE requirement for growth (NE g ) ranged from 1.26 to 4.66 MJ d −1 as average daily gains increased from 100 to 300 g d −1 , with a partial energy efficiency for growth (k g ) of 0.45. These results indicated that the NE g required by crossbred female lambs of German Mutton Merino×Inner Mongolia Merino was lower than the recommendation of the American or British nutritional system.