Sheep farmers are praying for a prolonged spell of cold weather to kill off a midge population that could be carrying the Schmallenberg virus.
Breeding for the main lambing is now underway and ewes in early pregnancy are at high risk of contracting the virus, which can result in abortions and malformed lambs.
IFA sheep chairman James Murphy said the discovery of two cases of Schmallenberg in Ireland in the past week was a concern for breeders.
Lambs affected by the virus have bent limbs, fixed joints, stiff necks, curved spines and nervous problems.
Farmers have been urged not to use excessive force when assisting the birth of deformed lambs and to contact their vet if they find aborted foetuses or newborn animals showing malformations or nervous signs.
"We will be hoping that a spell of dry, hardy and cold weather would kill off the remaining midge population," said Mr Murphy.
A stillborn calf on a Co Cork farm and a malformed calf on a Banbridge, Co Down farm tested positive for Schmallenberg last Tuesday and Thursday respectively.
A second calf on the Co Down farm tested negative for the virus, even though it displayed signs consistent with those associated with the disease.