Carcase yield improving following change to Terminal Sire Evaluation

In 2019 Signet changed the way in which we analysed the ultrasound muscle and fat depth data that we collect from sheep. Initially, we used to assess data on an age adjusted basis, whereas we now use weight adjusted data – which provides a better indication of the amount of muscle/fat in the carcase at a standard slaughter weight.

Historically carcase traits had been adjusted for age, however this meant that increases in muscling were confounded with increases in growth rate. The bigger the sheep, unsurprisingly, the bigger the muscle at a fixed age. Adjusting muscle/fat depths for weight provided a better indication of carcase yield, which we can now assess independently of growth rate.

Being a scanning technician, I have found that since 2019, breeders have moved to scan their sheep at an earlier age. This is advantageous in helping breeders to make early breeding decisions and more closely reflects their performance at a typical slaughter weight. They are also lighter to lift into the CT scanner!

Genetic trends for muscle depth, as seen in the graph below, have risen in most terminal breeds which means there is more saleable meat in the carcase and indicates breeders are making faster genetic gain in enhancing overall levels of muscling as a result.

Signet produces new EBVs/Indexes every month (whereas previously breeding values were only updated 3 times a year) and this approach feeds back vital information to breeders to inform commercial decisions about whether to keep animals for breeding or send them to slaughter.

The charts below show the muscle depth EBV’s over the last 23 years. It shows an increase in genetic gain since the change from age adjusted to weight adjusted carcase traits in 2019.

Interestingly they also show a levelling off in terms of changes in fat depth, with animals no leaner at a fixed weight than 5 years ago despite significant increases in growth rates. This trend probably reflects a change in both the way fat depth is now assessed and also the implementation of a small positive weighting on fatness within the terminal sire breeding index.