A statement from the Jockey Club on Wednesday revealed that samples were taken from 408 horses, and all tested negative for the use of EPO (erythropoietin).

"I hope that these results will serve to reassure the racing public," said the statement.

Pipe complained that the visits were "underhand", disrupting both his staff and his horses, and questioned the Jockey Club's approach.

"They've got the wrong way of doing things," he said. "I don't know why they've tested those five trainers.

"It's supposed to be random but I rather doubt that. If they don't test other trainers, I wonder why they've tested those five."

EPO allegations

The tests came after trainer Charlie Mann last year claimed blood-boosting substance EPO was being used regularly in British horse racing.

"This was principally an exercise to deal with the well publicised allegations of the use of EPO in racehorses," said the Jockey Club statement.

"We have spoken to the five trainers concerned and told them that the tests were all negative.