Why are oestrogenic clovers problematic?

Pastures containing oestrogenic clovers are thought to be widespread throughout Australia, especially in pastures sown prior to the 1970s. Recent surveys conducted in the medium to high rainfall zones of southern Australia have found that old cultivars of subterranean clover remain common in many pastures. Often they have persisted because of their hard seed or tolerance to waterlogging. High levels of oestrogenic compounds can negatively impact sheep health.

History

The link between sheep reproductive health problems and high levels of the oestrogenic compound, formononetin, in the leaves of sub clover was first made in the 1960s. In response, plant breeding programs quickly developed and released new cultivars with lower, safer, levels of formononetin. By the 1980s, the problem was thought to have been largely resolved. Thus,  communication about the problem declined and knowledge on how to identify and remediate highly oestrogenic pastures diminished.

How does grazing highly oestrogenic sub clovers affect livestock?

• most commonly, an increased dry ewe percentage
• unexpected low lambing percentages due to temporary declines in ewe fertility
• an increase in uterine prolapse
• an increase in ewe and lamb mortality around birth
• in severe cases, permanent loss of ewe fertility, milk secretion in maiden ewes and wethers, false bladders in wethers – ‘clover disease’.

Why might highly oestrogenic cultivars be common in a paddock?

High oestrogen cultivars can be very persistent. Even if they were sown > 25 years ago, they can now dominate pastures, even including some renovated pastures.

When might the presence of highly oestrogenic sub clover cause a problem?

If they contribute 20% or more of pasture biomass.