Date of this Version
Macfarlane, Lewis & Emmans in Animal Science (2004) 78.
The effects of for age type, breed type and sex on lamb growth and carcass composition, and their changes throughout growth, were measured. The three breed types were Scottish Blackface (no. =31), Suffolk (no. =28) and their reciprocal cross (no. =30). The lambs were given ad libitum a pelleted rye grass alone, pelleted lucerne alone or a choice of both. Each lamb was scanned using X-ray computed tomography to measure the weights of fat, lean and bone in the carcass at three proportions of mature body weight (0-30, 0·45 and 0·65). Live weights and food intake data were recorded weekly. Average daily gains in live weight and carcass tissues, food intake and efficiency were calculated for each lamb between degrees of maturity. Relationships between weight and food intake were investigated usinga Spillman function. Breed type had no effect on fat or lean proportion in the carcass but Scottish Blackface lambs had 1·04 times the carcass bone proportions of the Suffolk or crossbred lambs. Diet had no effect on carcass tissue proportions, The effect of sex on carcass composition changed with stage of maturity. Breed type and sex effects on intakes and gains in live weight and tissue weights were related to mature size differences. Scaling by (mature size)o·73 did notfully remove these differences. There were no effects of breed type, sex or diet on efficiency. Lambs on ryegrass had lower intakes (0·878 as great) and slower growth (0·851 as fast) than those on lucerne or the choice treatment. The mean proportion of rye grass in the choice diet was 0·366 (s.e. 0·0273); it increased slightly with time. There was no breed type by diet interaction for anyof the variables examined. The Spillman function described growth well andshowed that there were noeffects of breed type, diet or sex on efficiency.