Kelly Pearce, Graham Gardner, Fiona Anderson
School of Veterinary and Biomedical Science, Murdoch University

Why is lean meat yield important?
Lean meat yield – a definition: Lean meat yield percentage (LMY%) refers to the proportion of a carcase that is composed of lean tissue (muscle).
In Australia, 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 (i.e. more bone and fat) compared to beef, pork and chicken and is typically more expensive, especially when compared on a $/kg lean at retail. 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 increase deficiency in the boning room. These carcases require less labour to trim fat and there is less carcase wastage. 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.
How can producers improve LMY%?
Sheep Genetics Australia produces Australian Sheep Breeding Values (ASBVs) which are used to predict the performance of a sire for many economically significant wool and carcase traits. ASBV’s use performance information of an individual sheep, its relatives (pedigree) and its progeny to predict the breeding value of a sire. The 3 main ASBVs that we use to indirectly select for lean meat yield are post weaning weight (PWWT), C-site fat depth (PFAT) and eye muscle depth (PEMD). Combinations of these ASBVs are used to create selection indices for ranking sires eg. Carcase Plus.
What are these ASBV’s delivering?
Post weaning eye muscle depth (PEMD): The progeny of high PEMD terminal sires have increased weight of the loin and eye muscle area. Recent analysis of the CT data has also shown more muscle in the saddle but has also demonstrated that this offset by a decrease in the amount of forequarter lean tissue. Due to the value of the loin cuts this will have a positive impact on the value of the carcase. About 100gms of short loin per 7 units of PEMD.
Post weaning weight (PWWT) impacts on carcase weight: Increasing PWWT had its major economic influence by delivering heavier carcases earlier. Lambs with high PWWT values are faster growing and reach heavier slaughter weights or target weights sooner. Thus terminal sire lamb offspring had an increased pre-slaughter live weight and HCW of 3.00kg and 2.22kg respectively over 10 PWWT ASBV range. The impact of the PWWT ASBV is largely related to maturity at slaughter, with animals moving toward a larger mature size and therefore are at an earlier stage of maturity at slaughter. Even so, this is having only a small impact on LMY% and only in females.
Post weaning fat depth (PFAT): Decreasing PFAT gives a leaner more muscular animal. A decreasing PFAT value decreases whole carcase fatness. It has previously been thought that this would be a site specific effect, impacting at the site of measurement (C-site). Across a 4 unit range in PFAT there was shown to be on average a 13% decrease in carcase fat. This was offset by an increase in carcase lean and bone. Decreasing PFAT had no effect on the distribution of tissues within the carcase.
Conclusion
Lean meat yield % can be measured but this is currently difficult to do accurately at high speed in the abattoir. There are financial benefits of improving LMY% along the supply chain. LMY% can be manipulated using the Australian Sheep Breeding Values for growth, fat and muscling, with PWWT increasing size, PEMD increasing muscling and PFAT decreasing fat. It is important to monitor the impact of increasing LMY% on eating quality to maintain long term consumer satisfaction and confidence in the lamb industry.