In order to investigate the effects of type of breed on carcass composition, an examination was made of 361 lambs from four breeds: Clun Forest and Colbred (termed ewe breeds); and Suffolk and Hampshire (termed ram breeds). The animals were in four carcass weight groups averaging 15, 17, 19 and 21 kg.
Percentage subcutaneous fat was influenced more by carcass weight than by breed, whereas both carcass weight and breed had similar effects on percentage lean. At the mean carcass weight of 18 kg, Colbreds, the leanest breed, had a similar value for percentage lean (about 57 % of carcass tissue weight) to the carcasses over all breeds weighing 15 kg; and Cluns, the fattest breed, had a similar value (about 54%) to those weighing 21 kg. Since the ram breeds were intermediate in composition between the two ewe breeds there was no effect of type of breed on carcass composition. The breed differences were related to eventual mature size and to the stage of maturity at each carcass weight, as judged by body length and bone weight measurements. However, Colbreds were bigger and leaner than published estimates of their mature weight suggested. Humerus weight was a good predictor of lean or total fat weight, explaining 83 % ofvariation when used as a predictor along with carcass weight.
Type of breed had a marked effect on internal fat deposition, the ewe breeds having heavier weights of both kidney knob and channel fat (KKCF) and caul fat (omental fat) than the ram breeds; and on the length oflimb bones, the ewe breeds having longer but thinner bones than the ram breeds. The order of the relative growth of the tissues and fat depots was: subcutaneous fat > caul fat > KKCF > intermuscular fat > lean > bone. Therefore, the internal fat depots were later maturing than intermuscular fat.
The percentage of prime cuts in the carcass was not affected by carcass weight. Colbreds had significantly lower values than the other breeds. Suffolks had the lowest lean to bone ratio.