Cattle breeding company Genus is investigating a mix-up of semen straws that led to a number of prize-winning UK Jersey cows producing black-and-white calves.

The error was thought to have occurred at an American facility, but Genus declined to comment on where the mistake had been made.

This week British breeders were trying to assess the cost. One breeder told Farmers Weekly that many herds affected were set to lose large sums of money.

“We’re producing top-quality animals, not standard show animals,” said the breeder, who preferred to remain anonymous.

He estimated that the mistake would cost his businesses about £20,000 in direct losses alone and about five years of breeding, as two of the dams used in his breeding programme have since died.

“It [Genus] has offered us less than half of the value of the intended animals,” the breeder said.

A Genus spokeswoman said: “We produce 10m units a year and this kind of mistake happens once every 10 years. We are working with the farmers concerned to resolve the problem, but can’t comment on individual cases.”

The company would not be drawn on how it intends to ensure the problem does not occur again.