There will be no racing in Britain until February 13 at the earliest, the British Horseracing Authority has announced.
An outbreak of equine flu has caused a six-day shutdown, with racing's rulers set to make a further assessment on Monday as to when racing can resume.
News broke late on Wednesday evening that the virus had been detected and Donald McCain confirmed on Thursday that he has three confirmed cases in his yard.
Whilst the infected horses had not been racing this week, McCain has had runners at Wolverhampton, Ayr and Ludlow.
As a result, any trainer who ran a horse at those meetings has had restrictions placed on their movement.
No further positive tests have been recorded, but another three days are needed before it will be possible to make a decision on whether it is safe to resume racing as the disease can take that long to show its symptoms.
In a statement, the BHA said: This approach will allow samples to be collected and assessed by the Animal Health Trust in order that a fully informed decision can be made on Monday.
"This may then allow declarations to take place on Tuesday in time for racing on Wednesday, with 24-hour declarations for all fixtures on this day, should racing be able to resume. Declarations for Thursday would revert to the usual procedures.
"Trainers support a precautionary approach and we thank them for the collaborative manner in which they have worked with us to address this unfolding situation.
"We appreciate the impact that this may have on the sport commercially, but disease control in order to mitigate the risk of further disruption to the sport - and safeguard the health and welfare of our horses - must be a priority."
It added that a plan to reschedule this weekend's key races will be constructed.
An outbreak of equine flu has forced the cancellation of all British racing on Thursday.
The British Horseracing Authority (BHA) made the decision on Wednesday night after the Animal Health Trust confirmed three positives tests from vaccinated horses in an active racing yard.
In a statement, the BHA reported horses from the infected yard raced on Wednesday at Ayr and Ludlow, adding identification of the virus in vaccinated animals presented a “cause for significant concern”.
Donald McCain’s yard was the only one represented at both tracks.
The BHA statement added: “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.”
Thursday’s cancellations come less than five weeks before the start of this year’s Cheltenham Festival – the annual highlight of the National Hunt calendar.
It is not yet known how long the current shut-down of racing may have to last – but inevitably for thousands of racing followers, and of course those directly involved in the industry, there will be uncomfortable echoes of the foot-and-mouth crises of 1967 and 2001.
On each occasion, the racing calendar was affected for two months – and in 2001, the Cheltenham Festival was abandoned.
A further update on the possible continued extent of disruption is expected from the BHA – with a packed weekend of Cheltenham trials and other big races scheduled at Newbury, Warwick, Musselburgh and in Ireland.
The governing body’s statement added: “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 action to cancel Thursday’s races was taken with unanimous support of the BHA’s industry veterinary committee and will affect meetings at Huntingdon, Doncaster, Ffos Las and Chelmsford.
Equine influenza is a highly infectious disease of horses, mules and donkeys. Symptoms in non–immune animals include high fever, coughing and nasal discharge.
- Press Association