The duke took action to protect his prize herd

The Holstein herd is valued at millions of pounds because the bulls produce high-quality semen for breeding programmes throughout the United States, Europe and Australia.

They are part of the Duke's cattle-breeding company Cogent.

While life is now returning to normal for the animals, they are still being kept away from other cattle on the estate near Chester.

The herd was placed in isolation within days of the first outbreak of the disease in the UK in February.

As well as being supplied with filtered air, staff, including vets and studmen, operated a shift pattern to keep the animals under 24-hour surveillance.

Reduced security

A spokesman for Cogent said: "Our chief concern is for the well-being and welfare of the animals under our care.

"We have recently been able to reduce the very high level of bio-security we implemented for our bull stud some months ago, in response to the foot-and-mouth risk at that time.

"With the decreased risk of infection we have removed the plastic hoardings allowing greater circulation of fresh air for the benefit of the bulls.

"At the same time our staff have returned to a more normal care rota system.

Continued vigilance

"However, we are continuing to monitor the situation closely and remain vigilant, with rigorous anti-infection procedures still firmly in place."

Cheshire was due to be declared free of foot-and-mouth disease at the end of the month - but a new case has struck a farm near Warrington within the last two weeks.

More than 800 farms in Northwich, Macclesfield and Knutsford, infected during the second wave of the virus in May, have been given the all-clear.