Modelling relationships between host genotype and disease epidemiology in domestic animals: nematode infections in ruminant livestock.

Models of nematode infections which incorporate hosts genetics are reviewed. They demonstrate two general features of relevance to animal breeders: (1) that responses to selection are greater than predicted by quantitative genetic theory, being a function of changes in both host genotype and the disease epidemiology, with these epidemiological benefits enhancing productivity; and (2) when considering discrete units of resistance, e.g. genes for resistance, it is not necessary to make the whole population genetically resistant in order to greatly reduce the risk from the disease of concern. It is suggested that models incorporating both disease epidemiology and host genetics can, in the future, be used as decision-making tools to determine when selection for resistance to an infectious disease is an appropriate activity, to determine optimum balances between resistance and production traits in selection indices, and to predict possible rates of parasite co-evolution. This review has also been published in Animal Breeding Abstracts (1999) Vol. 67(7), pp. 547-553.