On March 13, USEF held a public workshop on the use of Depo-Provera, or medroxyprogesterone acetate, in competition horses. The stated purpose was to address concerns about the drug’s efficacy and safety, and to discuss the possibility of rule changes regarding its use at USEF-licensed competitions. Invited speakers included:

• Stephen Schumacher, DVM, chief administrator of USEF Drugs and Medications Program
• Patrick McCue, DVM, PhD, Diplomat ACT; Professor, Equine Reproduction Laboratory, Colorado State University
• Jim Heird, Ph.D., Glenn Blodgett Equine Chair, Executive Professor and Coordinator Equine Initiative, Texas A&M University
• Mary Babick, president, USHJA
• Sissy Wickes, trainer, owner, USEF “R” Judge, USHJA Board of Directors, editor of The Plaid Horse
• Geoff Vernon, U.S. Team vet, Canadian Team vet, and member of the Equestrian Canada Equine Medication Control Committee

An expert panel also took part, asking questions of the presenters. It included:

• Geoff Teall, hunter/jumper and equitation trainer and judge
• A. Kent Allen, DVM, chair of the USEF Equine Drugs and Medications Committee
• Laura Graves, Olympic dressage medalist
• Elisabeth Goth, vice president of the USEF Board of Directors and world champion Saddlebred breeder/exhibitor

The workshop was live-streamed online, and the USEF invited the submission of comments from the membership at 2017workshop@usef.org. The archived video, PowerPoint slides from the presentations, and links to various studies are available on the USEF website.

Here are 10 things to take away from the USEF workshop:

1. A horse that is “getting Depo” isn’t really getting Depo.

The brand-name drug Depo-Provera that we’re all familiar with—an every-three-months injectable form of birth control for women—was approved by the Food and Drug Administration in 1992. (But various other formulations of the drug had been approved and in use since 1959.) The chemical name of the drug is medroxyprogesterone acetate (MPA).

Depo-Provera has never been approved for use in horses, however, so the brand-name drug can’t be prescribed for that purpose. It can be compounded, however, meaning that pharmacists can create their own formulations using the same drug at the same concentrations as the name-brand version.

So although the common vernacular is to say that a horse is “on Depo,” it’s more accurate to say the horse is being given MPA.

2. Very little research has been done on the use of MPA in horses and research that has been done appears to show that MPA doesn’t have any biological effect on a mare’s heat cycles… 

MPA first began to be used in horses 30 years ago as an alternative to Regu-mate (altrenogest), which has long been used to control heat cycles in mares, but carries some pretty significant health risks for the human women who have to handle and administer it to horses orally. But MPA had never been studied in horses — there was no research on appropriate dosing, or the drug’s intended and unintended effects. Dosing amounts and frequency in the field vary widely, and the evidence of its effects is primarily anecdotal. (Both its short-term intended effects, namely controlling “mare-ish” behavior, and the seeming lack of any long term unintended health consequences.)

Dr. Patrick McCue and other researchers undertook a study that examined the effects of both altrenogest and MPA. The results were published in the peer-reviewed Journal of Equine Veterinary Science in 2009. The study included three groups of six mares: one group was given altrenogest (daily for six weeks), one was given MPA (an initial loading dose, and then weekly for six weeks), and a control group was given a sterile saline injection.

None of the mares on altrenogest showed behavioral estrus when teased by a stallion, developed follicles, or showed an increase in luteinizing hormone (LH) associated with estrus.. All of the control mares and all of the mares given MPA expressed normal estrus when teased, developed follicles and ovulated, and showed an increase in LH.

3. … but anecdotal evidence definitely points to some kind of effect.

“People [who use MPA on horses] have felt like there is an effect, a behavioral effect,” McCue said, adding that veterinarians get so many questions about the efficacy of various hormone treatments and really had no concrete evidence on which to base their recommendations. “We can’t answer questions with no data, so we did the study,” he said. “We didn’t set out to prove one thing or the other; we set out to get data so that we could understand. And it was a little more black-and-white than I even anticipated, that it has no apparent effect on reproductive cyclicity or behavioral estrus in the horse.

“I don’t have any doubts that people have seen other effects. I don’t know how why that effect occurs. but it seems like so many people utilize it say there’s an effect [that] I have to believe them. I just don’t know the effect is generated.”

4. MPA is actually already a prohibited substance in Canada.

“MPA is and has been a prohibited drug for use in competition horses in Canada,” said Geoff Vernon of the Equestrian Canada Equine Medication Control Committee. “We banned the drugs in Canada that appear on the Canadian Pari Mutuel Agency’s schedule as prohibited drugs. The Canadian Pari Mutuel Racing Association is the federal regulatory authority that oversees the racetracks in Canada. We also ban those products that aren’t licensed for specific use in horses. We also ban any drug that might either directly or indirectly affect the performance of a horse.”

While MPA was banned in Canada, Equestrian Canada didn’t start testing for it until 2016. “When we started testing for the product, we recognize now that our implementation of that testing procedure could have been better. We could have notified our exhibitors that we were actually now testing for MPA. We could have offered better guidelines in terms of what withdrawal time would be for those horses who had been administered MPA. And we failed to recognize as a committee the implications that testing for MPA would have in terms of not only the impact in sanctions and penalties, but also the effect it would have on our U.S. competitors coming into Canada to compete,” Vernon said.

So, positive tests for MPA in Canada now result in a notification and warning versus an actual sanction or penalty for 2016 and 2017.

Vernon noted that his committee researched why competitors were using MPA and noted that there are legitimate reasons to use MPA, “what we became alarmed at was—either because it failed to suppress estrus or something else—MPA was being administered at higher and higher doses and at greater and greater frequency, which we were quite concerned about,” said Vernon. “We felt the drug was acting more centrally and having sedative or tranquilizing effects when being used at high doses and for long periods.”

Because they perceived that MPA was being used without having been licensed for equine use and in an attempt to alter performance—both of which violated their medication rules—“We thought it was critical that we actually begin testing for MPA,” said Vernon.

5. Research in other species points to an effect on GABA receptors in the brain.

Dr. Stephen Schumacher spoke about the perceived calming effect that MPA has on both mares and geldings and stallions, and the possibility that it’s related to the fact that MPA reacts with GABA receptors to create an effect similar to tranquilizers. These receptors are very similar across mammalian species, so although the research hasn’t been done on horses specifically, it’s likely that the effect is similar to species that have been studied.

6. Definitions matter. What exactly is a “tranquilizing” effect? What “enhances performance?”

The bedrock of USEF’s medication rule has always been that any substance that “enhances” performance is forbidden. But normal therapeutic use of NSAIDs, or even supplements, could be considered performance-enhancing, some argue. So why target MPA, many wonder?

Dr. Geoff Vernon clarified that the effect should be considered “tranquilizer-like” or “sedative-like,” and shouldn’t be construed to have as significant an effect on a horse as an actual tranquilizing agent.

Proponents of MPA used different terminology—Mary Babick spoke of a “focusing effect” that makes horses easier to train, and a stress-relieving effect for horses in a very unnatural competitive environment. “I’m not sure it is a tranquilizer. I’ve ridden horses that are tranquilized,” she said, referring to horses being rehabbed from injuries. “There’s a big difference in riding a horse that’s been given a shot of Depo-Provera and a horse that’s been given a shot of Dormosedan [detomidine hydrochloride] or acepromazine. They don’t feel the same to me at all.”

But Dr. Schumacher pointed out that many of the anxieties being expressed and arguments being made sounded very similar to the discussions that happened when use of reserpine, a long-acting tranquilizer, was restricted. Although MPA works by a different mechanism of action, “those were the same kinds of terminology that were used at that time,” he said. “So the question has got to be, at the end of the day, is that performance-altering effect an issue for our industry?”

7. Members felt blindsided.

Sissy Wickes spoke about the fact that this possible rule change seemed to come out of nowhere and took the membership by surprise. “Dr. Schumacher, I think that you and your USEF cohorts have not served us well,” she said. “You have created the image of us against them, of men making rules in the back room with the door closed without our input, without our knowledge, because we’re either too ignorant or too malevolent to behave ethically. I think you have done our constituency a disservice in the way this has been handled.”

8. Many people don’t think MPA has any detrimental effects on the horse.

Wickes also provided numerous statements from competitors and veterinarians who felt MPA had no ill effects. Geoff Teall and Babick also pointed out that MPA has been in widespread use in horses for an extended period of time. Teall specifically noted that when reserpine was still in use, you could tell which horses were on it because they looked poorly, but there is no noticeable effect on horses being given MPA.

Many also expressed worries that, without MPA, competitors will turn to more lunging, or more harmful substances to achieve a calming effect… and that those methods definitely would be harmful to horses.

9. The general public’s perception of the horse show industry is important.

Dr. Jim Heird cautioned attendees to think of how the sport looks from the outside, and to be wary of becoming habituated to training methods or medications that are morally questionable. “We ignore those actions because we want to win and believe those practices are necessary to win,” he said. “We ignore them because we see successful people do them, and worse, we ignore what we see happening because we’re afraid of being embarrassed and ostracized for speaking out. Habituation prevents us from seeing that some or our actions and techniques are counter to our responsibility of protecting the horse and its dignity at our events.”

The show ring presents low-hanging fruit for activists, he said. “Each of us can think of things that are so obviously wrong in our shows and in our training that we can’t defend them to any rational person,” he continued. “If we as an industry don’t want outsiders or authorities dictating how we show and present our horses, we need to begin cleaning up what we’re doing wrong. I don’t think any of us want non-horse people making decisions about what we can and cannot do. Let’s fix what we can’t defend.”

10. There is no proposed MPA rule change… yet.

The USEF plans to take comments from the membership for a week after the workshop, and a non-binding recommendation will be made from the workshop panel to the board of directors at its mid-year meeting.

You can read much more in the article “USEF To Examine Rules On Depo-Provera And Regu-Mate” in the Feb. 27 print issue of The Chronicle of the Horse.