Four horses have now died in an outbreak of a highly contagious equine herpes virus in Hampshire.
Crofton Manor Equestrian Centre, near Stubbington, has been in quarantine since the first case of EHV-1 was confirmed on Tuesday.
Ten horses subsequently tested positive for the virus and the centre said it has placed itself on "lockdown".
The strain, which can cause inflation of blood vessels in the spinal cord and brain, cannot be passed to humans.
All horses at the Titchfield Road based centre - which hosts show jumping and dressage competitions - have been tested.
A spokesman for the centre confirmed on Sunday that two more horses had died - bringing the total to four - but that the majority of results had come back negative.
The New Forest Verderers said horses which have visited Crofton Manor since Christmas should temporarily refrain from visiting the national park.
- 9 January