24 May 2002

New index system to improve carcass

A COLLABORATIVE project is preparing to develop a selection index to improve carcass quality of longwool sire breeds and their progeny, while maintaining reproductive performance and maternal ability.

Will Haresign, director of the Institute of Rural Studies at Aberystwyth, said the project had taken place at IRS and ADAS Pwllpeiran between 1997 and 2000. A total of 45 performance recorded Bluefaced Leicester ram lambs had been crossed with 4500 Hardy Speckled Face and Scottish Blackface ewes.

Mule lambs produced were assessed for growth and ultrasonic fat and muscle depth. Wethers were slaughtered and assessed for carcass traits. The 1800 Mule ewes were retained at SAC Edinburgh, ADAS Rosemaund and IRS Aberystwyth to assess lifetime performance. They are being crossed with 90 high and low index Charollais, Suffolk and Texel rams over four seasons.

Prof Haresign said the first results were coming through. The 2208 Mule wether lambs reached a 2/3L fat score, in an average of 196 days. Average carcass weight was 15.9kg and 73% classified O for conformation. But dissections showed high index Bluefaced Leicester sires produced progeny with more lean and less fat in every joint.

Of the first 600 Mule ewes, 94% lambed at two years old. Those that did produced an average of 1.78 lambs a head and reared 84% of them.

Lambs weighed 15.6kg and 26.9kg at five and 10 weeks of age. They gained an average of 300g a day from birth to 10 weeks. Terminal sire cross lambs were finished at 3L fat score, which they reached in 179 days. Carcass weight averaged 18kg and 63% of carcasses classified R and 20% were Us.

High index terminal sires produced faster growing lambs and reached finished condition earlier. Their carcasses were heavier, with thicker muscles, less fat and more saleable meat yield.

"Important carcass benefits have been demonstrated in Mule wethers from selecting high index longwool crossing sires," said Prof Haresign, who emphasised that the same would be true of other widely used crossing breeds.

"Early results show promising growth and carcass benefits from using high index terminal sires. More comprehensive results, including a full evaluation of Mule ewe maternal traits, will be available in future." &#42

Selecting high index longwool crossing sires is proving beneficial, says Will Haresign.