Permanent infertility in ewes exposed to plant oestrogens.

In Australia, more than 1 million ewes have permanently damaged reproductive tracts because they have been grazed on oestrogenic pasture. These effects occur in the absence of classical clinical "clover disease". The lesions result from an "organisational" action of oestrogen, causing a mild sexual transdifferentiation to occur in ewes during adult life, with the main lesion being found in the cervix. Diagnosis of the problem depends primarily on detection of the pathological changes, rather than history or clinical signs. On average, affected flocks have around a 10% increase in non-pregnant ewes, but most farmers can achieve an acceptable lambing rate by increasing their management and feed inputs to produce more twin lambs. Agronomic approaches have been used in the past to combat "clover disease", but further progress with the present problem may depend on the development of animal-based solutions.