BREEDING FOR DISEASE RESISTANCE IN MERINO SHEEP IN AUSTRALIA

Breeding far disease resistance in Merino sheep in Australia has attra cted considerable research and development attention. Increased labour costs, the reduced efficacy of common anthelmintics and insecticides, consumer demand for products which are free of chemicals and the poor prognosis of alternative long-term control strategies are all forcing sheep breeders to contemplate the best animal health options availabl e, including selective breeding for resistance. The three major diseas es which affect sheep production include gastrointestinal nematode par asites, flystrike (cutaneous myiasis) and footrot. Genetic improvement has been shown to be feasible in all these diseases, possibly with li ttle adverse effect on genetic progress in other production traits. Pr ogrammes for resistance to internal parasites to be included in practi cal breeding programmes are now in progress. This paper deals with the incentives for focusing on the three major diseases in Merino sheep, the potential sources of genetic variation, and the means to exploit t hese sources of variation. The authors also highlight gains and benefi ts achieved in experimental selection flocks, and the difficulties and options available for commercial breeders.