The five-month-old koala lost his mum when a herd of bovines trampled her to death as she crossed their paddock at Mirboo North.

Many koalas are killed or injured each year when territorial cows with calves at heel act in concert to circle and trample koalas when they go to ground to change trees.

Wildlife Victoria experts said it sounded “bizarre”, but the killer instinct in cows in western Victoria and Gippsland was common knowledge among farmers and wildlife carers.

“I’ve had a joey come in after being found sitting on the back of a cow,” said Colleen Wood, who runs the Southern Ash Wildlife Shelter, where Sam the Black Saturday survivor lived.

“Its mother has been killed on the ground and the joey has climbed up the closest thing to her body, which happened to be one of the killer cows,” she said.

Ms Wood said that even a large male koala weighing 14kg could not survive being run down by a 500kg cow.

“I’ve seen them with every rib broken, with head injuries, with every organ ruptured,” Ms Wood said.

“One cow will see a koala and call the others over and they all trample and butt it.

“The poor koala has got nowhere to go and stands there stranded and takes it,” she said.

“They don’t have a strong fight or flight instinct, whereas a wallaby or roo or wombat would make a run for it.”

A male koala, aged about four, was put down in Portland on Monday after its jaw was shattered by a blow from a cow’s hoof.

Wildlife Victoria rescuer Sharon Webster said the helpless koala was seen lying on its back, trying to swat at the herd.

“The farmer grabbed a doona and picked it up and, bless him, put it on the back seat of his car where it could be kept calm,” Ms Webster said.

“But sadly its injuries were unsustainable.”

Wildlife Victoria’s Amy Amato urged farmers to investigate if their cows were bellowing and intervene.