Half of a herd of cows ate themselves to death after escaping from their pen in Western France.

Farmer Anthony Vaillant had failed to secure the door of a barn, allowing the 46 cows it housed to wander out. The animals made their way to a nearby food store at the farm near the town of Couëron, where the entirety of their winter rations was kept.

However, the food they ate was a type of high energy supplement which can be harmful if consumed in large quantities, and the cows proceeded to eat their way through an entire winter’s worth of the food in one sitting.

“It’s like an overdose,” Mr Vaillant told local newspaper Ouest-France. “If they are eaten in too big a quantity, these cereals stop the digestive rumen function of the cows. And when the stomach does not work the cow becomes intoxicated.

Mr Vaillant then had to helplessly watch as his herd began to die, despite enlisting help from a vet. In total, 22 cows died from over-eating. The remaining 24 animals can no longer produce milk.

Mr Vaillant hopes to rebuild his herd through donations and help from his neighbours.