Metabolisable energy (ME) intake and body compositional and energy changes were measured in grazing lambs weaned at 4 or 12 weeks of age and in light or heavy ewes offered 3 herbage allowances during early lactation. Body energy change (MJ/kg) from 4 to 12 weeks of age varied markedly between early weaned (7.4) and suckled lambs (13.4) because of different rates of body fat deposition but was similar for both groups (16.4) from 12 to 24 weeks of age. Average efficiency of utilisation of ME for growth was 0.38 and maintenance energy requirement 0.691 MJ ME/kg W0.75/d. The ME intakes of lambs were considerably higher than those estimated using MAFF (1975) and ARC (1980) data, particularly between 4 and 12 weeks of age. The energy content of body weight loss (MJ/kg) was greater in light (60) than in heavy ewes (37) because of a higher proportion of fat in weight loss in light ewes. Absolute body energy loss (MJ/d) was lower in light (6.3) than in heavy ewes (7.9), but ME intake (MJ/d) and milk energy production (MJ/d) were similar for each class of ewe.
Proceedings of the New Zealand Society of Animal Production, Volume 45, , 121-124, 1985
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