The National Stud in Newmarket has been closed to the public "for the greater good of Newmarket" following the discovery of an equine virus.
A filly currently based on the premises has been found to have contracted a virus and the stud's managing director Brian O'Rourke feels this was the most sensible course of action to take.
He said: "A case of neurological herpes virus infection has been identified in a filly who is in the health isolation unit at the National Stud.
"The filly arrived from overseas on January 20, 2016, and is fully vaccinated.
"We are therefore observing the requirements of the Codes of Practice and the main stud has now been closed on a precautionary basis.
"It is hoped that breeding activity can be resumed at the start of the covering season.
"We have taken these necessary measures for the greater good of Newmarket.
"That's why we've locked the gates and all being well there will be no more hiccups.
"We look forward to commencing tours in due course."
The National Stud is home to five stallions, including dual Group One winner Toronado, and also provides boarding and spelling services.