A Whakatane dairy farmer is rallying farmers across the country to help a South Taranaki couple who had 120 cows die on their farm this week.

About 15 vets rushed to the Oeo farm of Chris and Catherine Cook on Tuesday but could not save the dying animals, part of a herd of 600 and worth an estimated $400,000.

Vets are not saying what caused the deaths but had ruled out nitrate poisoning this morning.

And while industry bosses say the farmers would be unlikely to be insured against such an event, Whakatane dairy farmer Rod McPherson is calling on fellow farmers to help the Cooks out.

McPherson had contacted Fonterra to arrange for anyone who wanted to donate a cow to help rebuild the couple's livelihood to get in touch.

"They've set up a spreadsheet to take contacts of anyone who wants to donate an animal."

He said he would touch base with Fonterra later on to arrange getting the cows to Taranaki.

McPherson remembered the generosity of a farming couple who helped him out in the floods that struck the Bay of Plenty in 2004.

He said the farming community was great for helping each other out.

"It's just what we do, there must be 12,000 cows in the area so surely we can muster up 120."

He said five or six cows had been donated from the Bay of Plenty area already.

Mrs Cook's brother, John Murphy, said this morning the family was not ready to speak but was grateful for all the support they had received.

The couple, who have a young family, said farmers had offered them cows and people were taking meals to their house.

The wider community, including Fonterra and DairyNZ, was supporting the couple.

About 20 cows were still sick and were being looked after and milked only once a day.

The rest of the herd was fine.

Murphy said he thought it would be a long time before the couple were ready to talk about their ordeal.

Meanwhile, Newstalk ZB has reported this morning the cows died after a water trough was topped up with a portable tank used earlier to dissolve nitrogen.

But Taranaki Veterinary centre chief executive Stephen Hopkinson, of Hawera, said he would not release the cause without the permission of his clients.

"It'll be up the family to make that decision - when they're ready to discuss it," he said.

"But to avoid scaremongering, I can say it's not nitrate poisoning."

Murphy said he expected tests being undertaken by the Ministry of Primary Industries to take some time.

Federated Farmers Taranaki president Harvey Leach said most farmers didn't insure their herds because it was too expensive.

"Some farmers insure for electrocution, but that would be about it," he said.

"Cows die, that happens every year and you just can't afford it (insurance). It's just one of those ones where you just have to take the loss."