Clover disease is an induced infertility in sheep as a result of the animals consuming clovers containing high levels of oestrogenic compounds.

Clover disease was prevalent during the 1960s and 1970s when many pastures were sown to some older varieties of sub clover that were high in oestrogen.

While newer varieties do not have this problem, oestrogenic varieties have continued to increase in southern pastures from remnant populations and if not kept in check could potentially impact on sheep production again.

The two main problem varieties are Dwalganup, which was sown extensively in NSW, and Dinninup, which was a low level contaminant in uncertified seed from WA.

Both of these varieties are early maturing and have a high hard seed level helping them survive false breaks and dry springs.
Consequently, they have been able to persist in many paddocks.

It is important to note that not all older varieties are high in oestrogens and varieties released since 1990 such as Goulburn, Urana, Coolamon and Riverina have been screened for oestrogen levels before release.

The newer varieties are also higher in hard seed content.

Drought conditions during the past six years has seen sub clover set dramatically affected. Dwalganup and Dinninup will have had an advantage in seed set over later maturing varieties with low levels of hard seed and may now be the dominant remaining clover.

If one of your pasture recovery strategies is to increase the sub clover population by using the existing clover plants then you should check that they are not oestrogenic varieties.

Unfortunately, very few farmers or agronomists will be able to accurately identify sub clover varieties.

In practice, it may be easier to assume if you have not sown a paddock to one of the newer varieties it is likely to contain a high level of oestrogenic clover.

Sub clover plants that survive a long cropping phase are also more likely to be an oestrogenic variety so introduce new varieties when sowing back to pasture.

Include an earlier maturing variety in the sowing mix to compete with Dwalganup and Dinninup.

This may be important if drier conditions are going to be more prevalent.

There is an excellent Sub Clover Agfact on the NSW DPI web site which can help you choose the right variety for your area and identify oestrogenic varieties that may be in your paddocks.

Clover disease does not affect cattle and will only impact sheep flocks if more than 30 per cent of their diet is oestrogenic clover.

Infertility in a flock may be due to a number of factors, so consult your veterinarian if you have any problems.