31 March 2000

Booroola gene may hit weight

RESEARCH in New Zealand shows that the Booroola gene, which increases litter size in sheep, may have a negative effect on liveweight gain through genes piggy-backing one another during transfer.

Roslin Institutes Grant Walling said New Zealand flock owners had been disappointed to find that breeding with the Booroola gene had a downside.

"They want low maintenance sheep combined with the benefits of increased lambing percentage." But during breeding programmes the advantages of improved litter size were being outweighed by lower liveweights at weaning. This had a knock-on affect on an animals mature liveweight during its lifetime, he said.

"Lighter lambs always struggle to catch-up," said Dr Walling, who added that this finding almost spelled the end of work with the Booroola gene. But subsequent research identified an accompanying quantitative trait locus (QTL) affecting liveweight and not the Booroola gene.

When the Booroola gene was moved to crossbred sheep to improve their lambing percentage, a closely linked QTL piggy-backed its way across in the transfer and began to affect liveweight, he said.

That highlighted one problem of transferring genes through generations of back-crossing – it could drag in undesirable qualities as well, he added. "This study showed that the QTL affecting liveweight to weaning can hitch-hike with the Booroola allele."

Dr Walling said future work with the Booroola gene would need to break the link between it and the QTL that affects liveweight, if benefits of lambing percentage were to be gained without detrimental side effects. &#42