Fiona Anderson

Lean meat yield is a key efficiency and profit driver throughout the supply chain. Lamb is sold in lower yielding formats at a retail level (ie more bone and fat) compared to beef, pork and chicken and is typically more expensive, especially when compared on a $/kg lean at retail (Pethick, Ball et al. 2010). High yielding carcases deliver cuts that have a better shape and ensure retailers do not have to present products of overly fat animals for display and sale. For processors a high yielding animal represents increased efficiency in the boning room. These carcases require less labour to trim fat and there is less carcase wastage. For producers, higher yielding animals can be finished to heavier weights without becoming overly fat and accruing penalties. Additionally, fast growing, high yielding animals can be finished either faster or to heavier weights, in a shorter period of time, offering the producer savings on feed costs. The challenge is to produce a fast growing lamb that can be turned off quickly, that are of favourable conformation, and also gives a satisfactory return to the producer. It is increasingly important that price signals reflect not just more carcase as it may represent increasing amounts of fat. With continued evolution of the payment scheme of lamb there is the potential to improve profitability through the use of genetic selection for increased yield.

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.