British horses will not be allowed to race in Ireland until further notice.
Racing was cancelled at all courses in the UK on Thursday due to an outbreak of equine flu.
The British Horseracing Authority confirmed races at four venues were cancelled after three animals from a single yard tested positive for the virus.
The BHA warned that horses from that yard raced at Ayr and Ludlow yesterday, potentially exposing other animals, including some Irish horses to the risk of infection.
There were multiple Irish runners at both meetings.
Today's seven race card will proceed at Thurles this afternoon
Tests will be carried out to try and work out the extent of the disease after horses from an infected yard raced at Ayr and Ludlow yesterday.
Horse Racing Ireland says racing will continue here in the meantime as the disease risk status in racing Thoroughbreds has not yet changed.
The BHA consulted with its veterinary committee before making this decision and said:
"Racing was shut down today as a precautionary measure to restrict the movement of thoroughbred race horses and prevent any further spread of the virus.
"It was essential that racing be stood down today and controls on movements of horses be put in place in order to attempt to control the spread of the disease.
"The decision was taken swiftly last night that this course of action should be taken, once the extent of the issue was known.
HRI say a small number of isolated cases of equine influenza have been reported in Ireland over the last couple of weeks.
They add that the situation is being closely monitored in consultation with the Department of Agriculture, Food and Marine.