Resistance to worms in sheep is a heritable trait, which means this characteristic can be passed onto their progeny. There is considerable variation in worm resistance between individuals in a flock. Breeders can use this to their advantage when buying rams.
The WEC ASBV (Worm Egg Count, Australian Sheep Breeding Value) describes the value of an animal’s genes for carrying worm burdens. It is a combination of, being genetically less likely to pick up worms and being able to cope immunologically with the worm burden.
By selecting rams that are not only productive but also have a favourable ASBV, it is possible to improve the genetic resistance of your flock to worms. Worm resistant sheep take longer to achieve worm burdens that require treatment, as many of the infective larvae they ingest do not establish into adult worms in the resistant sheep. The benefits of this are:
- Fewer worm eggs are deposited onto the pastures
- Less infective worm larvae to re-infect the sheep
- Slower rate of infection
- Fewer drenches required each year
- Resilient sheep can better tolerate worms