Genetics - The inherent worm resistance of Merinos
In subtropical areas such as India and Indonesia, where livestock can become burdened with enormous worm loads, natural selection has seen the emergence of sheep breeds with exceptional worm resistance. However, these breeds lack the valuable wool and production traits of Merinos.
Australian geneticists have proved that Merinos can retain their productivity while achieving an equivalent level of worm resistance to their Asian counterparts.
The proof is in selection lines established 20 years ago in each of Australia’s different climate zones. A good example is the Rylington Merino line, founded by Dr John Karlsson of the Department of Agriculture and Food, Western Australia. In 2007, the line celebrates its 20-year anniversary as one of the most worm-resistant Merino flocks in Australia, while substantially improving production characteristics over the past two decades.
“We have found that the animals have cross-resistance to the major parasites, including barber’s pole worm, that cost the industry $400 million a year,” Dr Karlsson says. “However, the resistance does not seem to involve one or two genes of major effect, so molecular markers won’t provide a quick fix but a useful adjunct for breeding. Currently, selection is based on faecal egg counts (FEC), using test regimes suitable for different climate zones.”
With Sheep Genetics Australia already incorporating the FEC test into its Australian Sheep Breeding Values (ASBVs), Dr Karlsson emphatically believes that ram breeders can make substantial genetic gain by exploiting the genetic resistance inherent to Merinos.
Indeed, he has already done so on his own 2000 head of sheep. He started in the 1980s, when he sensed that chemical drenches and mulesing were in for long-term problems.
“On the back of that breeding, I stopped mulesing in 2000 and I have nearly phased out drenches,” Dr Karlsson says. He is adamant that there are whole-farm benefits to breeding for worm resistance and other ‘easy-care’ traits.
More information: Dr John Karlsson, jkarlsson@agric.wa.gov.au
See also: Vale to a bare breech trailblazer and Bare-breech rams opening frontiers.
Return to Beyond the Bale Issue 28 index page.