Neither the farmer nor representatives at the Limousin breed society would comment.
Over the past four years, the department has tested at least 549 samples from cattle here for bute – all of which tested negative for the drug.
A Food Safety Authority (FSAI) spokesperson said that they were not treating the new incident as a food safety issue because the bull in question had not entered the food chain.
A statement from the Department of Agriculture said that it would not be "appropriate to comment at this stage" of the ongoing investigation. It concluded that "there are no food safety concerns at issue".
The Irish beef sector is heavily dependent on exports, with more than 90pc of the 518,000 tonnes of meat produced here exported to premium markets such as Britain and Europe.
The meat industry here employs an estimated 20,000 people directly and indirectly.
While sales of frozen burgers fell dramatically in the wake of the discovery of horse meat in burgers produced at the Silvercrest plant in Ballybay, the sector ended 2013 with an 8pc increase in total output.
Q. What is bute?
A. Phenylbutazone, often referred to as 'bute', is an anti-inflammatory drug used to treat pain, sprains and fever in animals.
It was also used in human medicine for the treatment of arthritis in the past.
Q. Why is it banned?
A. It is no longer approved for human use due to its adverse side-effects and links to cancer.
It is also banned from use in horses in competition and racing due to its performance-enhancing effects.
And it was linked to the practice of 'rapping' show-jumpers to force them to jump higher.
Q. Why would a farmer use it on an animal?
A. A farmer with a valuable beef animal might use bute to help the animal ignore the pain of a knock picked up during transport to a show or an injury acquired prior to the event.
Due to the size of the animals involved at top-flight cattle shows, their limbs can be under extra pressure compared to standard commercial animals, making them more prone to going lame.
This would be the death-knell for their chances of winning in the show ring, and ultimately increasing their breeding value.
Top breeding bulls often fetch more than €10,000 in the auction ring.
Q. How could it get into the human food chain?
A. Experts differ on how long it takes for bute to break down in an animal's system.
But meat from any bute-treated animal could potentially carry the drug into the food chain.
Q. How long is the Department of Agriculture's investigation expected to take?
A. These investigations can often take weeks and months.
It is highly unlikely that the farmer involved will have recorded what animals have been treated with the drug. So all the animals on the farm will probably be blood-sampled, with any animals proving positive likely to be slaughtered and disposed of.
Q: What other action will be taken?
Animals sold from the farm at the centre of this investigation are likely to be subjected to the same tests, swelling the number of farmers involved in this investigation.
The nature of pedigree breeders' businesses means that they rely on the sale of breeding stock annually to other farmers to cover the cost of showing and acquiring the best genetics.
The vets linked with the breeders in this case are also likely to come under the microscope.
Slaughterhouses that killed animals from these herds will also be on the hit-list for the Department of Agriculture officials.