24 October 1997

CT offers genetic fast track

By Sue Rider

GENETIC progress in sheep could increase by up to 50% once use of a sophisticated computer method of assessing body composition is more widespread.

Geoff Simm of the Scottish Agricultural College, Edinburgh, told the Irish Grassland Associations Sheep Conference at Carlow last week (see p48) that computed tomography had the potential to lift rates of gain in carcass traits by up to 50% compared with selection using ultra-sound.

CT is a whole body scan which gives greater muscle depth accuracy than ultra-sound. "The CT scans give a much clearer picture of the difference between fat and muscle than ever achieved with ultra-sound," explained Dr Simm.

CT would be too expensive for widespread use, but there would be real benefits of targeting a small number of potential reference sires.

"To be cost-effective it must be integrated with on-farm ultra-sound scanning. For instance, CT could be used to select among potential reference sires in a sire reference scheme after initial screening on ultrasonic measurements. "We are now working on what the optimal % of rams is to scan by CT after selection by ultrasound. This is where the SRSs come in. A few rams will be widely used. If we select even better reference sires by CT, genetic progress will improve," said Dr Simm.

An estimated 16% of terminal sires in use come from flocks recorded using ultrasound. "This produces benefits for the industry worth about £4.75m a year."

At the same uptake, but combining ultra-sound and CT scanning, a return of up to £6.75m could be achieved. If uptake is increased to 25%, and selection still based on CT and ultra-sound scanning, expected returns could double.

&#8226 A CT unit has been established in Edinburgh by SAC and BioSS (Biomathematics and Statistics Scotland) and research is underway to investigate optimum use of the technique.

SAC is comparing CT measurements with ultrasound and carcass composition, determined by physical dissection and chemical analysis. "We will also scan about 3000 lambs from Suffolk, Texel, and Charollais SRS over three years," said Dr Simm. &#42

Genetic progress in action at Knockbeg sheep unit, Carlow, visited by the Irish Grassland Association at its sheep meeting last last week. Report p48.