Abstract
Increasing lean meat yield % and redistribution of lean tissue to more highly priced parts of the carcase will increase its value. Selection for the Australian Sheep Breeding Value (ASBV) for greater post weaning eye muscle depth (PEMD) increased eye muscle area and weight of the eye of the short loin, although had minimal impact on carcase lean meat yield %. We hypothesised that selection using the PEMD-ASBV would increase saddle lean weight, without altering whole carcase lean weight when animals were compared at the same carcase weight Lamb carcases (ie1218) from the Sheep CRC Information Nucleus were scanned in ‘quarters’ (fore, saddle, and hind) using Computed Tomography (CT) to determine fat lean and bone weights. Data was analysed using the allometric equation y=axb, fitted in its log-Iinearised form logy = log a +b.logx. Fixed effects were site-yeast sex, sire type, bulb-type rear-type and kill group within site-year, with random terms sire and dam by year. At a given carcase weight the lean tissue was 4.2% heavier (P<0.01), and fat 8.7% lighter in the whole carcase (P<0.05) across the 7 unit PEMD range. When compared at the same lean weight, the lean tissue in the saddle was 4.9% heavier (P<0.01), and lean in the forequarter was 4.8% lighter (P<0.01) across the PEMD range. Aligning with our hypothesis, there was more lean tissue in the saddle, although unexpectedly this was at the expense of the forequarter only. The mechanistic reason for this redistribution is not clear, and will be investigated with more extensive sampling from tissues across the carcase. In contrast to our hypothesis, PEMD was associated with increased total carcase lean, and reduced fat. The leaner and more muscular composition appears to be independent of maturity as there was not a corresponding increase in bone weight. These impacts on lean weight and distribution to the loin will increase carcass value.