Ryegrass staggers are rife in some farming regions where rain has fallen following prolonged dry weather.
South Wairarapa vet Peter Morris said "grass staggers" usually arrived in summer or autumn and this year the problem has been more pronounced because of the drier conditions.
The fungi that creates the toxinbringing on grass staggers grows in the seed heads and lower stems of ryegrass.
Afflicted animals suffer from head wobbles, stiff legs and can take what appear to be seizures.
Mr Morris said symptoms are worse when stock is being moved or otherwise "excited".
Most stock will recover without the need to call in a vet, he said.
Mr Morris said lifestyle farmers who may not have a lot of experience, and people driving in rural areas who see sheep that seem to be having "fits", are those who should be made aware of the onset of grass staggers.
Lester Fletcher, a pasture scientist at Agresearch's Lincoln centre became a world leader in researching endophytic fungi after showing in the early 1980s that an endophyte was causing ryegrass staggers in livestock.
The endophyte also protected the ryegrass against Argentine stem weevil -- a serious pasture pest.
