This warning comes from Lincoln University’s Professor Derrick Moot who says the warm, wet weather experienced in many parts of New Zealand is conducive to the development of fungal infections in lush 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 10-14 days before they go to the ram. They can be returned to the crop immediately after they have been mated.
“The highest risk of having problems with lucerne is in an autumn like this which has been wet with high humidity.”
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 ewes 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.
Moot says the last year that produced similar problems was 2014 when a wet autumn depressed lambing rates by 10-20% for ewes and hoggets mated on lucerne. Since then a PhD study at Lincoln University has investigated the causes and effects of elevated coumesterol on lucerne and shown 10-14 days off the lucerne is sufficient to reverse any potential effects.