SUMMARYThe effects of slaughter weights on light lambs (n=45): 22.3 ± 2. 8 kg and 60 ± 2.4 days of age and heavy lambs (n=21): 43. 1 ± 6.3 kg and 169 ± 8.9 days of age on carcass and meat quality of 24 females, 23 cripthorchid and 19 castrated Corriedale (n=21) and Hampshire Down x Corriedale (n=23) and Southdown x Corriedale (n=22) lambs was studied. Slaughter weights affected (P≤0.05) all carcass characteristics evaluated. Heavy lambs had better conformation (0.320 vs 0.190 kg / cm, 1.09 vs 1.07, 55.7 vs 51.9 carcass and leg compacticity of heavy and light lambs, respectively), better fat grade (15.7 vs 7.3 mm GR, heavy and light lambs, respectively) and more favourable tissue composition (2.9 vs 1.9 meat/bone, 2.5 vs 2.2 meat / fat, heavy and light lambs, respectively). Nevertheless, light lamb carcasses had a better commercial yield of high value cuts than those of heavy lambs. Interms of the measurable quality characteristics of meat, only the pH was affected by slaughter weight. In the sensory analysis, sex and cross only affected meat tenderness. Meat from females or castrated lambs was more tender than cripthorchid lambs, particularly if they were crossbred lambs. Slaughter weights affected all sensory characteristics, with the meat from heavy lambs receiving the best scores in terms of tenderness, flavor quality and acceptability.

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The aims of the present study were to describe intermuscular differences in meat-quality traits in 15 young-sheep muscles, and to study the associations between meat quality and fibre typing across all (pooled) muscles as well as in previously selected homogeneous contractile–metabolic groups of muscles (slow-oxidative, intermediate and fast-glycolytic muscles). Meat-quality traits (pH, colour, expressed juice, cooking losses, tenderness and sarcomere length) and fibre typing were evaluated after 24 h of slaughter in 15 muscles from five cross-bred young sheep. Across all the studied muscles, intermuscular differences in some meat-quality traits (pH24, a* and expressed juice) seemed to be mainly explained by muscle oxidative activity, while intermuscular variation in other meat-quality traits (L*, b* and Warner–Bratzler shear force) were mainly explained by differences in fibre sizes. Within fast-glycolytic muscles, larger fast-glycolytic fibres and reduced oxidative activity were generally associated with lower ultimate pH, higher L* values, lower a* values and longer sarcomeres. Within intermediate muscles, larger fast-glycolytic fibres and reduced oxidative activity were generally associated with lower ultimate pH, higher L* values, shorter sarcomeres and reduced meat tenderness. Within slow-oxidative muscles, larger fast-glycolytic fibres and reduced oxidative activity were generally associated with lower amounts of expressed juice, lower a* values and reduced meat tenderness. The present study has contributed to a better understanding of the influence of muscle fibre types on intermuscular meat-quality variation, suggesting that although muscle fibre diversity may explain, at least in part, intermuscular differences in meat quality, these associations can also slightly vary among muscle contractile–metabolic groups.

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