Effects of available nutrition and sire breeding values for growth and muscling on the development of crossbred lambs. 2: Composition and commercial yield

Carcasses from 56 lambs representing male progeny of 3 sires selected for muscling (M sire-type), 3 sires selected for postweaning weight (G sire-type), and 3 control sires (C sire-type) were evaluated. Lambs had been raised on low (LOW) or high (HIGH) planes of available nutrition from 10 days of age to approximately 8 months when they were slaughtered at an average cold carcass weight (CCW) of 21.4 kg. When adjusted for CCW, M lambs had more lean tissue in the loin, a greater depth and width of the M. longissimus thoracis et lumborum at the 12th rib, and a greater weight of major hindlimb muscles than did G or C lambs. Although there was no difference in GR tissue depth due to sire-type at an adjusted CCW, there was less total fat in the carcass of M lambs and the amount of fat in the carcass of M lambs on HIGH nutrition was not greater than that on LOW nutrition, as it was for C and G lambs. This reduced propensity of M lambs to deposit fat in the carcass in response to HIGH nutrition was particularly evident in the loin, with fat-trim from the loin decreasing for M lambs in response to HIGH nutrition, whereas fat trim increased for C and G lambs compared at an adjusted CCW.