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This article was published in 1981
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Oestrogens in Lucerne
J.W. Plant, Special Veterinary Research Officer, Veterinary Research Station, NSW Dept. of Agriculture, Glenfield
There have been several enquiries recently concerning the oestrogens present in lucerne and their possible effect on the fertility of sheep and cattle. Some concern has been expressed that some of the newer varieties of lucerne may cause infertility.
The oestrogens present in lucerne belong to the coumestans, which include coumestrol, methoxycoumestrols, trifoliol, medicagol, lucernol, sativol, repensol and wariol. They occur in lucerne, white clover and soya beans and probably several other legumes.
CLINICAL SYNDROMES ASSOCIATED WITH THE COUMESTANS
Cattle: the effects are those of hyperoestrogenism i.e. sterility, some abortions, swelling of the udder and vulva in virgin heifers, endometritis and irregular oestrous cycles. Cystic ovaries and nymphomania have also been reported.
Pigs: clinical signs of oestrogens are often associated with oestrogens produced by fungi on grain. There is a swelling of the vulva, with congestion and oedema of the vulval lips and there may be a vaginal prolapse.
Goats: lucerne and clover hay has been suspected of causing 'low fertility rates, delayed pregnancy, low fecundity with single kids and twins of male sex, false pregnancies and lactation problems'.
Sheep: low twinning rates have been recorded in ewes that grazed on lucerne prior to mating. The low twinning rates are due to low ovulation rates caused by coumestans present in the lucerne.
Coumestans have no effect on oestrus or signs of oestrus in the ewe.
In the ewe, the effect on ovulation rates have been shown to have a linear relationship to the coumestan content of the feed, fed immediately prior to oestrus i.e. within 7 days. It has been suggested that in sheep, the coumestans act by inhibiting the expected increases in multiple ovulations following improved nutrition
Factors influencing the Coumestan levels in Pastures
There are some minor variations between strains, but season has little effect. The major accumulation of coumestans occurs later in the growing season in older plants and, is associated with an increase in the incidence of foliar disease. Foliar diseases may be the result of fungal, viral or insect infestations.
There is often an increase in oestrogenic activity in silage.
Levels in lucerne at the cutting stage (when 10 per cent of the crop is in bloom) have ranged from 0.2 ppm to over 200 ppm. Levels as low as 25 ppm can affect ovulation rates in sheep.
Reducing the Effects of Coumestan in Fertility
In sheep there is a high degree of recovery if ewes are withdrawn from the affected pasture 11 days prior to mating.
In general, sheep or cattle which are being joined should not graze on lucerne or other clover pastures which are showing evidence of foliar disease. These pastures should be grazed by other stock. Management should aim to have breeding stock being joined on young actively growing lucerne with no evidence of foliar disease.
If breeding stock being fed on hay or silage show signs of excess oestrogens in the diet, then the source of feed for these animals should be changed.
There is no evidence that coumestans cause a permanent infertility in sheep, similar to that seen with the oestrogenic isoflavones in some varieties of subterranean clover. The effects in cattle, goats and pigs are not clearly understood. The effects are likely to be more permanent in animals developing an endometritis or cystic ovaries.