A number of trainers appear set to face an anxious wait on whether they can have runners when racing resumes on Wednesday following the six-day shutdown due to equine influenza.
The British Horseracing Authority reports 221 declarations were made across the four fixtures at Plumpton, Southwell, Musselburgh and Kempton - with 16 eliminations from races being over-subscribed, leaving a total of 195 runners.
However, flu tests for some stables are yet to be known - meaning five of the 195, from four different yards, have already been withdrawn and some further non-runners may yet result.
The BHA said in a statement on Tuesday afternoon: "The team at the BHA are working through the evening to clear as many horses as possible to run tomorrow, working with the Animal Health Trust in analysing the data from returned equine influenza swabs.
"(Of the 195 horses declared) at present 190 have been cleared to run, with five horses from four trainers withdrawn at this stage. This is a precaution, where the BHA has not received notification that the horse or yard is free of the equine influenza virus.
"These trainers are all those who had runners at the fixture at Ayr on February 6, where a horse who was infected with the equine influenza virus had competed.
"The BHA is working with the affected trainers in order to explain what steps will be required in order to move their yards - or horses from their yards - to cleared status.
"The BHA wants to assess more data from the yards who had runners at Ayr before the yards who had runners are cleared. This is being treated as a priority by the AHT.
"Of the remaining 190 declarations there remains a number (22 at time of writing) that the BHA is working hard to clear this afternoon. A selection of trainers have been contacted and advised that their declarations stand for the moment, but they will only be able to run if test results are received by the BHA by this evening.
"In any cases where the declarations cannot be cleared, the horses will be declared non-runners in the morning."
Brant Dunshea, chief regulatory officer for the BHA, said: "The BHA is operating a risk model which identifies the level of potential exposure at each yard in order to determine which yards - and in some cases individual horses - are identified as safe to run.
"These controls were identified as absolutely necessary in order to permit a return to racing. A small number of individual trainers may be inconvenienced as a result of this until they are cleared to race, but in order to ensure an entirely level playing field it would have been necessary to place the entire sport on hold for at least seven more days.
"The measures we are following are intended to minimise the risk of spread of the disease and the subsequent impact this would inevitably have on owners, trainers jockeys and everyone else connected with the affected horses.
"The BHA is grateful to owners, trainers and vets for their understanding, and our teams are working around the clock - alongside those of the Animal Health Trust - to ensure that yards are cleared to race as soon as possible."