CT scanning helps detect superior genetics in sheep

Computed tomography (CT) scanning accelerates genetic improvement, provides live eating quality estimates and could help cut methane output.

This is according to SRUC sheep geneticist Nicola Lambe, who spoke at a webinar on terminal sire breeding (17 November) at the Sheep Breeders Round Table online conference.

She said CT scanning is an increasingly important tool for identifying superior genetics within flocks.

The equipment uses low-level X-rays from a source that rotates around the sheep to generate cross-sectional images.

See also: Guide to CT scanning and how it can benefit your flock

New traits

Lambing ease

It is possible to measure the pelvic width, height and area along with a calculation of the angle between the pelvis and spine, Dr Lambe said.

These traits proved to be highly heritable and matched lambing difficulty scores.


A close correlation has been found between methane output and the size of the reticulo-rumen in the sheep’s stomach. Animals with larger reticulo-rumens produced more methane in trials.

Cross-referencing revealed a high heritability, which could allow methane emissions to be brought under genomic control.

This achieves greater accuracy of measurements at up to 96%, compared to ultrasound scanning at about 60% accuracy, Dr Lambe suggested.

The equipment can now measure:

  • Weight and percentage of fat, muscle and bone in the carcass
  • Killing-out percentage
  • Muscle-to-bone and muscle-to-fat ratios
  • Muscle distribution
  • Gigot shape
  • Vertebrae number and spine length
  • Predicted intramuscular fat
  • Eye muscle area across the loin.

Once measured, results and carcass data are cross-referenced with estimated breeding values to provide reliable breeding information.

However, whole-flock scanning is not cost-effective, with charges ranging from £55-£98 a lamb – although some regions offer subsidies of up to 50%.

Instead, ultrasound is used to identify the best 15-20% of animals in a flock to go forward for the CT scanner.

Breeder experiences

Irene Fowlie, Essie flock

Sheep breeder Irene Fowlie’s Essie flock has seen a trebling of genetic merit since CT scanning began 10 years ago.

Ms Fowlie uses the Edinburgh-based scanning service to improve genetics and muscularity in Suffolk rams and females for sale or to rear as replacements.

Since 2010, the Essie flock has sent 147 rams to the Edinburgh scanning unit. These are initially selected from the wider flock by eye before confirmation from ultrasound results.

Last year at scanning, Essie lambs were 4kg heavier and had 2mm more muscle depth than the Suffolk breed average.

Scanning has also been used to detect and breed from 21-vertebrae animals that have higher muscling, weight and length.

A key benefit for the flock is the added confidence and assurance that can be given to buyers.

Ms Fowlie makes up a catalogue of detailed performance characteristics ahead of sales for buyers to select the best rams to meet their needs.

Scott Brown, Capielaw Suffolks

Scott Brown of Capielaw Suffolks has increased ram values through genetic improvement and greater assurances for customers

The flock started using CT scanning five years ago, with ultrasound identifying candidates at 21 weeks old.

Information gleaned from CT scanning has created greater transparency and assurance for customers, adding value, Mr Brown said.

“I can quickly provide potential buyers with detailed information, including fillet size and potential eating quality through intramuscular fat measurements. This is far more valuable than the existing grid system, which doesn’t reward farmers for quality.”

He attributed CT scanning results for helping to achieve more than £1,000 for a ram at Kelso sales in September.

Of the Capielaw ram lambs sold at Kelso, the 10 that had been CT scanned achieved an average of £260 more than animals that had not, Mr Brown added.