Genetic resistance in sheep to parasitic nematodes - A review

Parasitic resistance is an economically important trait for sheep industries because of heavy economic losses in the form of anthelmintic treatment as well as reduction in live weight, fertility and survivability of sheep. Conventional approaches including medication, pasture rotation, sanitation and improved nutrition minimizes the losses due to parasitic infection up to some extent, but these measures are no more effective for control of parasite. Breeding for parasitic resistance is an alternative option to reduce the cost of anthelmintics as well as minimize the adverse effects of parasites on sheep production. Parasitic resistance in breeding programme may be incorporated, if gene (s) of interest conferring resistance could be identified. Identification of gene/marker will allow early selection of genetically superior animals followed by their introgression would accelerate the genetic progress of resistance into susceptible breeds through breeding programme. Investigation of QTL or linked markers is a challenging area of research, due to the involvement of several genes and their complexity. However, combination of new technologies including mapping, candidate gene approach and the advances in functional and comparative genomics will also help in enhancing the progress in the detection and improvement of parasitic resistance in sheep.