A Taranaki farming family is mystified at the sudden death of 120 cows on the property in one day.
The cows at the Oeo property owned by Chris and Catherine Cook started falling to the ground half an hour after water troughs were topped up from a portable tank on Wednesday.
Mrs Cook's brother, John Murphy, says a number of vets quickly arrived but there was little they could do to save the cows which were part of a herd of 600. He says the family is very distressed.
The Ministry for Primary Industries will investigate what caused the deaths.
A spokesperson for Dairy New Zealand, Dr Nita Harding, says the industry organisation will coordinate offers of help for the family, which include replacing the cows.
Dr Harding says it was an unfortunate set of circumstances and the farmer did nothing wrong.
Federated Farmers, Taranaki vets, the Rural Support Trust and Fonterra are involved in helping the farmers.