A racehorse owned by Queen Elizabeth II named Estimate has recently tested positive for a banned substance. Trained by Sir Michael Stoute, the five-year-old mare came up positive for morphine, the result of which was likely due to a contaminated feed product.

"Five horses, under the care of various trainers, were affected. I can confirm that one of those horses was Estimate," said John Warren, racing adviser to Queen Elizabeth. "Initial indications are that the positive test resulted from the consumption of a contaminated feed product."

"A positive result is 99.99% of the time due to a feed contamination," said trainer and veterinarian Jim Boyle in an interview on Radio 5. "Morphine comes from the opium poppy. There have been studies done whereby ingestion of a poppy-seed bagel or a poppy-seed cake can cause a urine sample, 16 to 24 hours later, to test positive for morphine."

Last week, the British Horseracing Authority (BHA) revealed that five horses had tested positive for the drug and that they were conducting a full investigation into the matter. Warren noted that Sir Michael was "working closely with the feed company" to uncover which products were contaminated and was continuing to offer "his full co-operation" with the BHA.

In 2013, Estimate made international news when it became the first racehorse owned by a reigning monarch to win the Gold Cup in the race's entire 207-year history. Though that win will likely stand, Estimate's recent second place finish in the Cup last month could be in jeopardy.