Effects of food quality on growth and carcass composition in lambs of two breeds and their cross

The effects offood quality, breed type and sex (ram and ewe) on Iamb growth and carcass composition, and their changes throughout growth, were measured. The three breed typeswereScottish Blackface (B; no. = 24), Suffolk (S; no. = 28) and their reciprocal crosses (X; no. 33). The lambs had free access to a nutritionally non-limiting food, H, or a bulky food, L. Each lamb was scanned using X-ray computed tomography to measure the weights offat, lean and bone in the carcass at three degrees of maturity (0·30, 0·45 and 0·65) in live weight. Live weight and food intake data were recorded weekly. Average daily gains in live weight (ADG) and carcass tissues, intake (ADI) and efficiency (EFF = ADG/ADI) were calculated for each lamb between degrees of maturity. Gompertz and Spillman functions were used to investigate relationships between weight and both time and cumulative food intake. There wasa breed byfood interaction forfat and lean proportions (P \u3c 0·05). Only onH wasthere a breed difference (P \u3c 0·05) with S having less fat and more lean than either B or X, which did not differ from each other (P \u3e 0·1). On food L there were no breed effects (P\u3e 0·1). Across breeds, sexes and stages of maturity! food L caused lambs to have0·810asmuchfat and 1·063as muchlean compared with H (F \u3c 0·00l). There were breed byfood interactions for ADG (P \u3c 0·05) and EFF (P \u3c 0·01). ADG on L wasO· 72 of that onH for S, as compared with 0·79 for B and X. EFF on L was 0·463 of that on H for S, as compared with 0·586 for B and X. These were such that S was more sensitive to food effects on growth. The Gompertz and Spillman functions described growth well