Haemoglobin Type and Fertility of Merino Ewes grazing Oestrogenic (Yarloop Clover) Pastures

Abstract

CLOVER infertility disease in sheep is attributed to the high concentrations of oestrogenic substances found in certain legumes such as subterranean clover, variety Yarloop¹. Reduction in flock fertility can be as high as 75% with additional losses of lambing ewes due to dystocia^2,3. Where large areas of these clovers are grown, as in western and southern Australia, the economic loss is considerable. Significant progress has been made in selecting clover varieties which have a low oestrogen content⁴ but replacement of established oestrogenic species has had limited success and the cost of renovation is often prohibitively high. We wish to report some observations which suggest that it may be possible to select and breed animals likely to be resistant to clover infertility disease using existing flocks classified on the basis of their haemoglobin (Hb) type.