The Genetics of Parasite Resistance in Sheep

Abstract

Results are summarized of a series of studies designed to quantify the genetic basis for resistance and resilience in Haemonchus contortus infected sheep and to obtain estimates of productivity responses to selection for these traits. The heritability of resistance to infection was estimated at 0.30–0.40, but the heritability of resilience was too low to allow substantial progress by direct selection for this trait. It was concluded that selection for polygenically controlled resistance would lead to substantial progress for this trait and would also increase productivity of infected animals whilst not affecting productivity in the absence of infection. Moreover, evidence was obtained for the presence of a major resistance gene and it was shown that practical breeding strategies exploiting such a major gene would lead to dramatic improvements of resistance to infection with H. contortus .