Racing at Doncaster, Huntingdon, Ffos Las and Chelmsford was cancelled due to an equine flu outbreak.
All horse racing meetings were cancelled in Britain on Thursday due to an outbreak of equine flu.
The British Horseracing Authority (BHA) revealed there is a concern that the disease could spread after three vaccinated horses in an active racing yard tested positive for equine flu.
Meetings at Doncaster, Huntingdon, Ffos Las and Chelmsford were abandoned as a result of the outbreak.
A BHA statement late on Wednesday said: “The British Horseracing Authority (BHA), with unanimous support of the BHA’s industry veterinary committee, has taken the decision to cancel racing at all British racecourses on Thursday 7 February 2019.
“This is following the BHA being informed this evening by the Animal Health Trust of three confirmed Equine Influenza positives from vaccinated horses in an active racing yard.
“Horses from the infected yard have raced today at Ayr and Ludlow, potentially exposing a significant number of horses from yards across the country and in Ireland.
“The fact that the cases have been identified in vaccinated horses presents a cause for significant concern over welfare and the potential spread of the disease and the action to cancel racing has been viewed as necessary in order to restrict, as far as possible, the risk of further spread of the disease.
“The BHA has worked quickly to identify which yards could have potentially been exposed today and identify the further actions required. The BHA is presently communicating with yards potentially exposed to ensure appropriate quarantine and biosecurity measures are put in place and horse movements restricted to avoid possible further spread of the disease.
“The full extent of potential exposure is unknown and we are working quickly to understand as much as we can to assist our decision making.
“The BHA is working closely with the Animal Health Trust and will issue a further update tomorrow. We recommend that any trainer who has concerns about the health status of any of their horses should contact their veterinarian.”