Lincoln University’s Professor Derrick Moot says warm, wet weather is conducive to the development of fungal infections in lucerne crops. The plant responds to these infections by producing coumestrol, an oestrogenic compound which suppresses ovulation, particularly in young sheep.
While ewes can be flushed on the crop, Moot says ewes should be removed 1–14 days before they go to the ram. They can be returned to the crop immediately after they have been mated.
Moot says the weather conditions which increase the risk of elevated coumestrol levels in lucerne typically means there is plenty of grass available, and this should be the first option as a feed over mating.
From a flock perspective, the mixed-age ewes are less susceptible to increased coumestrol levels than ewe lambs.
Where there is limited pasture available, he suggests keeping the ewe hoggets on lucerne while the mixed-age ewes are mated and then swapping them around – provided the ewe hoggets are off the lucerne 10–14 days before they go to the ram.
Moot says there is no quick test available to test coumestrol levels but ewe lambs can be used as the canary in the mine. If, after grazing lucerne, ewe lambs develop pronounced udders and/or teat elongation then coumestrol levels will be elevated.