Authors : A.F.T. Amarante and M.R.V. Amarante
Abstract: Control of gastrointestinal nematodes in sheep relies heavily on anthelmintic treatments of the flocks. This strategy has been frequently useless as a consequence of the appearance of nematode populations with resistance to drugs. An alternative to alleviate the problems associated with chemotherapeutics is the breeding of sheep for resistance to nematodes. As the resistance to parasites is heritable, the efficiency of worm control can be increased through objective and accurate identification of genetically resistant individuals and an understanding of mechanisms underlying such genetic resistance. Mechanisms responsible for resistance are not fully understood. However, the development of resistance against nematodes has been associated with a response mediated by lymphocytes Th2 CD4+, increase in mast cell numbers in mucosa, eosinophilia, production of specific antibodies, increased mucus production and the presence of inhibitory substances in the mucus. Since resistant breeds are generally poorly productive, simple substitution of a susceptible, productive breed by a resistant breed is not always a viable option. Mapping genes for resistance will possibly allow marker-assisted selection based on individual quantitative trait loci. It may be possible to utilize resistance genes from a resistant breed by introgression through backcrossing into a more productive breed using marker assisted selection.
A.F.T. Amarante and M.R.V. Amarante , 2003. Breeding Sheep for Resistance to Nematode Infections . Journal of Animal and Veterinary Advances, 2: 147-161.