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×lnner 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-l, 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-~ DM, respectively. The NE requirement for maintenance （NEro） was 255 kJ kg-1 BW0.75, and the ME requirement for maintenance （MEre） was 352 kJ kg-I BW~.75, with a partial energy efficiency for maintenance （km） of 0.72. The NE requirement for growth （NEg） ranged from 1.26 to 4.66 MJ d-1as average daily gains increased from 100 to 300 g d-1, with a partial energy efficiency for growth （ks） of 0.45. These results indicated that the NEg required by crossbred female lambs of German Mutton Merinoxlnner Mongolia Merino was lower than the recommendation of the American or British nutritional system.