17 August 2001

Suffolk sires resistance trait

SUFFOLK sheep can begin to be selectively bred for natural resistance to worms after the publication of a new estimated breeding value.

The EBV is not incorporated into the Suffolk Sire Reference scheme index, but gives producers a further option when selecting terminal sires.

Worm resistance has high heritability, similar to liveweight or muscle depth, so progress through selective breeding is possible, says MLCs senior geneticist Gert Nieuwhof. He believes this trait will improve flock health and have a significant environmental impact.

"Organic producers are particularly interested in the new value, as they can select replacement terminal sires to gradually improve immunity to worms. Selectively improved animals will also benefit commercial flocks, as worm burdens in pasture will be cut – worm resistant animals spread fewer eggs," he says.

But an end to worm drenching could take 5-10 years to become a reality in improved flocks, he adds.

The EBV, developed by Mr Nieuwhof, is based on the analysis of 1000 faecal egg counts (FEC) from 20-week-old Suffolk lambs in the breeds Sire Reference Scheme.

Lambs were drenched four weeks before sampling to kill off any existing worms. To challenge lamb resistance, they were put on infected pasture. Lambs with natural immunity fought off worm burdens, so when examined, their faeces contained fewer worm eggs.

"When looking at a rams FEC EBV, the lower the figure the fewer worm eggs counted. Values range from high resistance at -0.7 to low resistance at 0.7," says Mr Nieuwhof.

Next year, he is encouraging all Suffolk breeders to participate in the resistance sampling so other sires can be included.

More breeds are planned for inclusion and this September will see the publication of FEC EBVs for the Texel SRS. &#42