How does ultrasound scanning enhance Terminal Sires?

In recent years there has been an increasing number of breeders have had their lambs measured using Signet’s ultrasound scanning service as part of their breeding programmes. It is a great tool to identify sheep with superior muscling, while avoiding those likely to be excessively fat. This is the best way of identifying animals with superior genes for muscling and this data is used to produce Estimated Breeding Values (EBVs).

What is ultrasound scanning?

The UK sheep industry were pioneers in the use of ultrasound scanning technology to assess muscle and fat levels across the loin in live animals.

In fact, the ultrasonic measurement of muscle depth, taken over the third lumber vertebrae, along with a measurement of liveweight, is a highly effective predictor of muscle yield. Studies have shown a high correlation between the prediction of meat yield obtained by on farm ultrasound measurements and the highly accurate “real” amount as determined using Computed Tomography (CT) scanning.  Additionally, work completed as part of the RamCompare project has highlighted strong correlations between Muscle Depth EBV and Carcase Conformation EBV. This provides clear evidence that on farm ultrasound scanning is doing an excellent job in identifying breeding stock with the right attributes for the modern consumer at a very effective cost to the Breeder and Industry.

The Muscle Depth EBV takes into account measurements collected on all known relatives and is by far a better predictor of genetic merit than the animal’s own measurement, which can be influenced by age and feeding.

Breeders have made significant progress to increase muscling within the carcase and as a result of selective breeding we see larger differences between breeding lines by recorded and unrecorded sires, which can be attributed to an increased uptake of ultrasound scanning technology and a recent change in the way we assess carcase traits to identify the higher yielding animals.

Historically carcase traits were adjusted for age, however this meant that increases in muscling were confounded with growth rate. The bigger sheep, unsurprisingly, tended to have larger muscles at a fixed age.  In the UK, whilst lamb growth rate is important (and EBVs for this trait are readily available), lambs tend to be slaughtered at a fixed weight (and ideally a similar level of finish).  For this reason, Signet changed the Terminal Sire Evaluation in 2016 to highlight genetic differences in lambs when killed at a similar slaughter weight.

This is change was important for a maternal breeding programme as it enabled producers to breed lambs with a better yield of meat in their carcase without increasing ewe mature size. This is an important consideration in breeding programmes that aim to enhance the efficiency of the breeding ewe.