Khama Kelman

The Australian lamb industry uses Australian Sheep Breeding Values for reduced postweaning subcutaneous fat depth (PFAT) to select for leanness and increased lean meat yield. Selection for reduced PFAT results in increased loin muscle weight (Gardner et al 2010) potentially leading to lower oxidative capacity in muscle (Greenwood et al 2006). Isocitrate dehydrogenase activity (ICDH) is an accepted indicator of aerobic metabolism, and therefore we hypothesise that selection for reduced PFAT results in a decrease in ICDH levels.

Introduction - Due to the nutritional importance of iron and zinc in human diets, marketing campaigns for lamb and beef are often focused on these minerals. Iron and zinc are associated with muscle aerobicity which may be diminishing in lamb meat due to selection practices targeting leanness and muscularity to increase lean meat yield (Pannier et al. 2010). Aerobicity of muscle has also been linked to intramuscular fat (IMF) percentage, and like-wise IMF is also depressed through selection for leanness (Gardner et a!. 20 I 0). Poor nutrition will also reduce carcase fatness and JMF, potentially limiting the scope for other genetic factors to impact. Therefore it seems plausible that the impact of selection for leanness will be less in a poor nutrition environment. Thus we hypothesised that selection for leanness would reduce carcase fatness and IMF, reduce aerobicity, and therefore reduce iron and zinc concentration, but these impacts will be depressed within flocks maintained on sites with poorer nutrition.