“I knew nothing about it until afterwards,” he said.

“I’ve spoken to a lot of people and no one knows about it.”

Mr Webber had been weaning his cows, so they were hungry when they were let out into a pasture containing kikuyu.

Uralla vet Jo Hoad, who treated the cows, said it was “not that common and not well understood”.

“The symptoms can look similar to milk fever,” she said.

The damaged was caused by oxalates in the grass, which form crystals in cow’s kidneys, causing a rapid drop in their calcium levels.

Mr Webber wants his story to be a cautionary tale to others. “Had I known, I could have taken steps to prevent it – it happened in a hurry when it happened,” he said.