Oxfordshire trainer Eve Johnson Houghton is the latest trainer to come forward and reveal one of her horses has tested positive for morphine.
The Didcot handler has confirmed the three-year-old gelding Charlie Wells failed a drugs test after winning the 32Red Classified Stakes at Chepstow on June 23, after which he has been placed in two other races.
She is mystified as to where the contaminated food was contained and has had all of her string tested as a precaution.
"I had all my horses tested, but they haven't come up with the results yet," said Johnson Houghton.
"I don't know which bit of feed it's in, but hopefully we'll get to the bottom of it, and hopefully it's a one-off."
Johnson Houghton admitted to using some products provided by animal feed manufacturer, Dodson & Horrell.
Earlier yesterday that company announced it was holding a full investigation into how possible component contamination could have occurred after Estimate, owned by The Queen, also tested positive for morphine.
Initial indications are that the positive test taken from the 2013 Ascot Gold Cup winner resulted from the consumption of a contaminated feed product, Buckingham Palace said in statement on Tuesday evening.
The Palace said Her Majesty has been informed of the development.
Dodson & Horrell, horse and dog food manufacturer to The Queen since 2006, identified Alfalfa Oil Plus as the possible product which had been contaminated but that it may not have happened on its premises.
The company said it has launched a "thorough investigation" with an unnamed supplier of the product.
Dodson & Horrell believes contamination could have come from poppy seeds that occur naturally in the environment.
A statement issued on behalf of Dodson & Horrell read: "Preliminary investigations suggest that any contamination of this component product did not occur at Dodson & Horrell's site.
"The investigation is currently centring on Dodson & Horrell's supplier.
"Dodson & Horrell has recalled batch numbers week 20-28 of Alfalfa Oil Plus as a precautionary measure, in accordance with our procedures and NOPS (naturally occurring prohibited substances) protocol.
"No positive test results have been recorded in any other Dodson & Horrell product currently in the market.
"From information currently available to us, it appears that any contamination may have come from poppy seeds that occur naturally in the environment. Please note this does not affect the welfare of the animal.
"Investigations are ongoing through the official and correct channels.
"Information will be shared by Dodson & Horrell as it becomes available."
Estimate, trained in Newmarket by Sir Michael Stoute, produced one of the headline stories of last season with a nail-biting triumph in the Gold Cup at the Royal meeting.
She then went down narrowly to Leading Light in the defence of her crown last month.
The five-year-old mare is reportedly still in contention for the Artemis Goodwood Cup next Thursday and worked yesterday morning over nine furlongs in Newmarket alongside stablemates Snow Sky and Top Tug.
The Queen's Fiery Sunset also won in her colours at Lingfield yesterday.
The three-year-old, trained by Michael Bell got off the mark in pleasing fashion in the Aldermore Block Discounting Maiden Stakes under champion jockey Richard Hughes.
The British Horseracing Authority announced last week that five horses under the care of various trainers have been reported to show the presence of morphine in their 'A' samples.