Roundworms are considered to be the most costly animal health condition of Australian livestock, costing sheep producers up to $500 million per year in lost productivity. The Australian Merino accounts for 75% of the national flock and is particuarly susceptible to roundworm infections. Roundworm infections of sheep often result in reduced fleece weight, fibre diameter and staple length and in severe cases death may result. In addition, producers have the added impact of control and treatment costs. Drug treatment is the control method of choice, but control is threatened by the evolution of drug resistance in roundworm populations. New strategies for control are urgently needed in order to improve sheep health and welfare, as well as maintaining wool quality.
Eosinophils, a specialised white blood cell of the sheep immune system, have been shown to play a major role in reducing worm length and fertility. Research performed by the immunogenetics research group at the AgriBio Centre for AgriBioscience have demonstrated that sheep that are resistant to infection with roundworms demonstrate high blood eosinophil counts, as well as lower faecal egg counts and smaller worms as compared to roundworm susceptible sheep. It is currently unknown whether this same correlation exists for eosinophils at the site of infection, the stomach, as well as how eosinophils are able to reduce worm fertility and length.
Selective breeding of sheep that are resistant to roundworms is an effective strategy for control, however this strategy often requires many years to establish a resistant flock. A better understanding of exactly how eosinophils are able to promote resistance to roundworms will provide valuable information for the development of a point-of-care diagnostic test to identify roundworm resistant sheep. This will allow wool producers to make informed animal management decisions on-farm by testing their flock for roundworm resistant sheep. An on-farm diagnostic test to identify resistant sheep will help to maintain wool production and reduce treatment costs for producers.