Together, they were responsible for the health and wellbeing of donated, former race horses that had been retrained for life after the track.

But on Tuesday, Michelle Steele and Dennis Mitchell were hit with a string of charges, under the Australian Rules of Racing, following a Racing NSW inquiry into alleged horse cruelty and mistreatment at the Australian Turf Club's mounted security division.

As well as ceremonial duties on race days, the horses were used by the ATC as props-for-hire at festivals, private functions and in modelling shoots, as well as for television shows including Australia's Next Top Model.

However, according to explosive evidence aired at two Racing NSW hearings, all was not well behind the scenes, with ATC employees having allegedly engaged in a "deliberate program" of sedating the retired throroughbreds so they would behave during gruelling shifts.

As the ATC's Mounted Security co-ordinator, Ms Steele has been charged with two counts of improper conduct relating to the care and welfare of horses under her supervision.

Along with Mr Mitchell, who is the ATC's general manager of security, risk and investigations, she has been issued with two charges of failing to provide veterinary treatment when necessary and an additional count of conduct prejudicial to the image of racing, which relates to general treatment of the animals and their stabling conditions.

While both employees refused to comment when approached by Fairfax Media on Wednesday, the ATC released a statement stating it "accepts" the findings of Racing NSW stewards.

"Unfortunately it is alleged that on occasions over the past two years two staff members ... breached the Australian Rules of Racing," ATC chief executive Darren Pearce said.

"Whilst those two members of staff are very disappointed with the charges, they are reviewing them and considering their options."

In a series of shocking allegations, stewards were told how the retired racehorses were systematically dumbed down with Sedazine paste and liquid acepromazine (ACE) - an injectable sedative that can only legally be given by a vet.

It is also claimed that pain from long shifts, poorly fitting saddles and general mistreatment was routinely masked by regular doses of the anti-inflammatory drug phenylbutazone, which is only recommended for short-term use.

Despite an investigation having originally been launched by Racing NSW in mid-January following a string of complaints, it was only when Fairfax Media exposed the scandal - more than a month later - that racing's peak body went public with information about the inquiry.

Since then, the number of witnesses who came forward more than doubled. One was former employee Chantal Lunardon who told the hearing: "Every time the horses were deployed for a security job, photo shoot or ridden through Centennial Park, they were sedated.

"I walked into the tack room and I observed them [staff] drawing up oral syringes of a liquid I knew to be ACE. At this point, I observed one employee hold the head of the horse while another administered the ACE over its tongue."

Mr Pearce said that Ms Steele and Mr Mitchell would "remain on restricted duties away from direct contact with horses" until the Racing NSW process had run its course, at which time the ATC would determine its "future actions".

"The ATC will continually work with Racing NSW and other authorities in maintaining the highest standards of care and management of our horses," he said.

Racing NSW said a hearing of the charges would follow, including any recommendations about the future operation of the ATC Mounted Security Division.

The RSPCA is running its own independent investigation into claims of mistreatment at the stables.