Effect of nutritional restriction and sire genotype on forelimb bone growth and carcass composition in crossbred lambs

The aim of this study was to assess the effect of low or high whole-of-life nutritional planes on bone growth, maturation, and carcass composition in lambs from sires (n = 9) with high estimated breeding values (EBVs) for post-weaning eye muscle depth (PEMD) or liveweight gain (PWWT), compared with sires of industry average for both traits. Lambs (n = 54) were killed at 8 months of age before measurement of forelimb bones, radiographic scoring, and histological measurement of growth plates, and bone ash mineral analysis. A subset of these (n = 36) had carcass composition serially assessed during growth by CAT-scan. Results reveal that the nutritional restriction imposed in this experiment caused signifcant restriction of skeletal growth, as reflected by shorter, thinner forelimb bones, altered limb proportions, narrowing (and in some cases permanent closure) of growth plates, and an altered bone mineral profile. CAT-scan analysis showed restriction of bone growth was similar to that of muscle growth. Progeny of high muscling (PEMD) sires showed greater muscle growth, but were possibly more susceptible to some of the skeletal effects of nutritional restriction. Greater sire EBVs for PEMD, PWWT, or fat depth were associated with narrower growth plates, suggestive of slower longitudinal bone growth and shorter adult limb length, although bone mass was not affected according to earlier CAT-scan data. Results also suggest that progeny of high PEMD or PWWT sires are earlier maturing in terms of skeletal (or at least limb) growth, although their bone mineral pro. le (magnesium content) was more consistent with that of physiologically less mature animals.