Mechanisms of immune-mediated scouring in parasite-resistant Merino sheep
Symptoms of parasite-infection in sheep include reduced weight gain and scouring (diarrhoea). Control of parasites in sheep has relied heavily on treatment with anthelmintic chemicals. This reliance has led to a high level of parasite resistance to anthelmintic treatment. A long-term, sustainable solution is to breed sheep that are naturally resistant to parasites on the basis of low faecal worm egg counts. However, scouring is not reduced in these resistant sheep and in some environments is significantly increased. The aim of my research is to discover the mechanisms underpinning this increased scouring in parasite-resistant Merino sheep. The results of this research will help researchers to identify sheep that are both resistant to parasites and not susceptible to scouring.
Nematode parasites cost the Australian sheep industry approximately $500 million every year. There is a need to develop clean, green and ethical parasite-control methods due to parasite resistance to chemical treatment and consumer demand for meat and wool produced with a minimum of chemical inputs. Harnessing the natural immunity of sheep by breeding for parasite-resistance is a long-term and sustainable solution. However, it has become apparent that in adult sheep scouring is often due to the immune response of the sheep rather than the effects of the parasite (‘immune-mediated scouring’). Therefore parasite-resistant sheep may scour just as badly as or even worse than susceptible sheep. Scouring leads to a build up of faecal material on wool around the breech. This reduces the value of the wool, pre-disposes sheep to flystrike and is a major source of microbial contaminants in meat carcasses. Therefore it is crucial to understand the mechanisms underpinning immune-mediated scouring so sheep can be bred that are both resistant to parasites and not susceptible to scouring.