The impact of carcase estimated breeding values on yield and quality of sheep meat

The aims of this study were to investigate the impact of carcase estimated breeding values on carcase size and lean meat yield of lambs and to determine whether nutrition alters these responses. Selection for high estimated breeding values for growth increased carcase size by as much as 4 kg in lambs fed a high plane of nutrition. On a low plane of nutrition, this effect was reduced by 60%, highlighting the importance of nutrition for realizing the potential of this trait. Selection for estimated breeding values for muscling reduced total carcase fatness by 3% in lambs fed at a low plane of nutrition and by 10% in lambs fed at a high plane of nutrition, resulting in an increase in lean meat yield and improved economic returns for sales based on a lean-meat-yield grid. Selecting for estimated breeding values for low fat depth reduced total carcase fatness by 4%; this effect was the same whether lambs were maintained on high or low planes of nutrition. Other aspects of meat quality maybe influenced by using sires selected for muscling. Meat tenderness may be reduced due to greater connective tissue content, but it is likely that this can be controlled by concurrent selection for growth. Juiciness and flavour may be reduced due to reduced intramuscular fat content, but this can be attenuated by nutritional practices and, in the longer term, by alleviating the negative selection for fatness. Selection for a combination of muscling and growth estimated breeding values in terminal sires is an excellent way to increase both carcase size and lean meat yield of lambs - and to provide greater returns for producers

Genotype and gender effects on sheep limb bone growth and maturation: selection for loin depth causes bone hypotrophy

This study aimed to compare limb bone growth between offspring of typical crosses used in Australian prime lamb production. Limb bones from sheep of five genotypes - Merino (M × M), Border Leicester sire × Merino (BL × M), Poll Dorset sires selected for growth × Merino (PDg × M), Poll Dorset sires selected for eye muscle depth (PDm × M) × Merino, or second cross (PDg × BLM) - at four time points from 4 to 22 months of age (n = 593) were dissected, measured and weighed. Growth curves were fitted within genotype groups and used to compare (i) overall limb bone growth in terms of length and weight, (ii) differences in allometric growth coefficients for individual bones, (iii) relative limb bone proportions, and (iv) maturity proportion. Results showed two distinct phenotypes in terms of limb bone growth: (i) relative bone hypotrophy of lambs from PDm × M, suggesting that selection for loin depth (PEMD EBV) may be linked with smaller limb size and that their higher muscle:bone ratio may be due to a relative decrease in bone rather than increase muscle weight; and (ii) Merinos were found to have comparable limb length to terminal sire crosses, although distal limb elements were proportionately longer at the expense of the proximal segments that are associated larger muscles. There was a general lack of major differences in bone growth between sheep very different in other production traits, particularly when compared allometrically. Thus, differences in bone growth, proportion or skeletal maturation were greater between ewes and wethers than between these divergent genotypes. PD m × M and BL × M were found to be earlier maturing in terms of limb length, although the bone mineral profile (magnesium content) of PDm × M was suggestive of relative physiological immaturity

Sheep genotype, age and muscle type affect the expression of metabolic enzyme markers

The objective of this study was to determine whether genotype, age (4, 8, 14 and 22 months), sex (ewe and wether) and muscle type influence ovine (n = 587) muscle metabolic characteristics. The genotypes represented were Poll Dorsetgrowth × Border Leicester Merino, Poll Dorset growth × Merino, Poll Dorsetmuscling × Merino, Merino × Merino and Border Leicester × Merino. Between 4 and 22 months of age, myoglobin concentration within all muscles and all genotypes doubled, with the bulk of this response occurring between 4 and 8 months of age. Levels in the longissimus thoracis et lumborum (LT) and semimembranosus muscles were double those seen in the semitendinosus (ST) muscle, and Merinos had the lowest myoglobin concentrations of all genotypes. The other aerobic indicator, isocitrate dehydrogenase, had lower activity in the ST compared with the LT, was lower in 22-month-old sheep compared with all other ages, and decreased as selection for leanness increased. Both phosphofructokinase and lactate dehydrogenase activity tended to increase with age, were lower in the ST compared with the LT, and had higher activity in the Border Leicester × Merino sheep. The correlation between the percentage of total myofibre area comprising type 2X myofibres and metabolic markers was far higher for the oxidative indicators isocitrate dehydrogenase and myoglobin, which both decreased as relative area of type 2X fibres increased. However, the strongest correlations were with the relative area of type 2A myofibres, which were consistently high for both oxidative and glycolytic metabolic markers implying positive coregulation with both energy producing pathways