An isolated case of anthrax disease in a cow was confirmed at a farm in Wiltshire following the death of the cow.
Movement restrictions were imposed at the farm and the animal’s carcass was incinerated. No other animals have been affected.
The previous outbreak in livestock in Great Britain was in 2006.
Public Health England said the risk of infection to humans was "very low" following the discovery.
Thousands of farmers from across the country are expected to attend the Dairy Show today in Somerset. It's taking place at the Royal Bath and West Showground.
Milk prices are likely to be high on the agenda.
And more than 250 top quality dairy cattle will be competing for the prestigious Supreme Dairy Championship.
An inquest has heard how Sandra Wiltshire and her pet dog Bruce were killed when they were trampled by cows in Chippenham last October.
The inquest in Salisbury is being heard in front of a jury who were told there was no public right of way through the field.
The jury was told that a fellow dog walker had found Sandra following the attack. She then lost consciousness and never recovered. A farmer told the inquest he believed the presence of a dog in the field would have caused the cows to react and trample Sandra.
Two dairy farmers from Dorchester are defying convention by milking their herd of 500 cows in the field in a mobile milking parlour. The cows and and parlour move around the 900 acres of rented pasture.