Martin Cake

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.

Animal maturity is an important concept in the meat industry, with emphasis on producing less mature (i.e. “physiologically younger”) animals with superior carcase characteristics such as greater tenderness and lower fatness. Unfortunately the concept of ‘maturity’ remains poorly defined. Where specified, ‘maturity’ usually refers to some proportion or index expressed relative to the mature state, in which the animal is in anatomical and/or compositional equilibrium. However indices of maturity referenced to body weight or composition (e.g. muscle:bone ratio) are problematic for assessing genotypic effects in modern prime lamb production, where terminal sires may be selected for specific compositional traits such as rapid muscle growth or low body fat. In such cases it may be preferable to define other indices such as skeletal maturity, by staging development in relation to longitudinal bone growth and mineral maturation.