There are several studies that have shown Depo has no effect on estrus suppression in mares, but there are equine veterinarians who disagree with this.
So, What is Depo exactly?
Depending on how your vet prescribes or recommends use, you must administer Depo intramuscular (IM) injection either weekly, bi-weekly, or monthly. There has been no conclusive research done on appropriate dosing for Depo. Therefore the dosage and amount given can vary throughout the horse world. There are also beliefs that Depo has an anti-anxiety effect on horses, which has not been proven in studies. Several top veterinarians believe this behavioral effect might be true, but there is no scientific data to support this theory.
Depo comes in normal or double-strength dosages. Thus, reading the labels on any medication you administer is always of utmost importance. Not doing so when handling a medication could lead to serious complications or death.
There are several studies that have shown Depo has no effect on estrus suppression in mares. There are however equine veterinarians who disagree with this. Some argue that they see more suppression of the heat cycle when horses are on Altrenogest or Regumate. Unfortunately, the downfall of Regumate is that it is difficult to administer because it is dangerous for women to handle. Altrenogest now comes in an injectable form, also administered IM. However, it is significantly more expensive than oral Regumate.
USEF Steps InSo, knowing that Depo has the potential to be ineffective… You can imagine how it confused a majority of the Hunter/Jumper horse show world in 2017 when USEF proposed a ban on DEPO. USEF tried to restrict the use of Depo because they said that it was being used in high quantities to quiet horses. They had little to no concrete or credible evidence to back this theory up.
This sent a majority of the show world into an uproar. There was so much opposition to this proposed rule change that the USEF held a workshop on March 13th, 2017. Speaking with professionals about their concerns and the proposed rule changes surrounding Depo was the goal. This workshop got live streamed online on the USEF website so if members could not attend, they could observe and submit suggestions/questions to be read at the workshop.
Vets Speak Up
Dr. Steven Schumacher, a veterinarian who spoke at the workshop, said that there is a possibility that Depo reacts with the GABA receptors in the horse’s brain to create a “tranquilizing effect.” Thus altering a horse’s behavior to better improve performance. Again, there is no definitive study on this theory.
USEF bans any medications that they feel enhance a horse’s performance. This is what led to their insistence on a ban on Depo. Many professionals argued that NSAIDs (also known as Non-Steroidal Anti-Inflammatory Drug) also enhance a horse’s performance and help the horses who need a little assistance perform their daily jobs better.
Therefore, the reason for this immediate ban of Depo didn’t make sense. Why was this specifically being targeted but nothing else? It seemed no one could accurately answer that question. Sissy Wickes, a prominent trainer, and R-judge argued that the United States Olympic Committee (USOC) does not perceive this drug to be performance-enhancing. Due to the fact that female human athletes have the approval to be on Depo-Provera and compete. It also worried many professionals that banning Depo could lead to people finding more dangerous drugs to use or lunging horses more frequently for longer periods of time.
USEF Keeps Members Involved
USEF stated they would take suggestions and questions for a week after the workshop. This, while they decided on the next step in the process of banning Depo. But the only change that occurred at that time was that starting September 1st, 2017. Trainers needed to fill out an MPA Disclosure Form before every show, stating which horse is on Depo, the amount being administered, the source of the medication, the reason for the use of the drug, the administration route, and the last administration date. This would allow for the USEF Board of Directors to assess the data collected from members on each form and would lead to them determining further action into a ban or regulation on Depo use. It would also help them determine accurate withdrawal times for Depo.
Canada Says NO To Depo Use
Canada banned the use of Depo because they observed that Depo was being administered in their country with increased frequency and in high dosages. Equestrian Canada also bans any medication or drug that they believe “either directly or indirectly affects the performance of a horse.” They felt that because of the higher doses of Depo being administered, Depo must have been improving the horse’s behavior and therefore putting them at an advantage over their competition. This led to their rule change and is why they now test for Depo.
Unexpected Depo-related Deaths
In 2019, the U.S. saw several unexpected Depo-related deaths in horses. In the last three years, there has been a correlation of 23 equine fatalities to Depo use. Reports have stated that the drug was properly administered intramuscularly but was still fatal to the horse. The conclusion was met that these horses died from anaphylaxis, which is an allergic reaction to Depo.
This led to a follow-up meeting of the USEF Depo panel in October of 2019 to review a petition by numerous veterinarians requesting that USEF ban the substance. The Panel determined that Depo has no therapeutic use in competition horses, as it does not interrupt estrus in mares, as was originally thought. Additionally, the United States Food and Drug Administration doesn’t approve (FDA)Depo for use in horses. As a result, the Panel voted unanimously to recommend that Depo have a place on the list of USEF prohibited substances.
As of December 1, 2019, the prohibition of MPA in horses competing at USEF-licensed competitions is active. However, due to the length of time involved for MPA to clear a horse’s system, sanctions for a positive test result began on June 1, 2020. The USEF has classified Depo as a Category III substance which has a penalty range starting at a 3-6-month suspension and a fine of $3,000-$6,000 for a first offense.
Sissy Wickes Powerpoint Presentation shown at USEF workshop
USEF Board of Directors Prohibits the Use of Medroxyprogesterone Acetate
Medroxyprogesterone Acetate Found to Have No Therapeutic Use in Competition Horses and has Been Linked to Anaphylaxis and Fatalities; Ban Effective
December 1, 2019
From the US Equestrian Communications Department
About the Author
Nicole Mandracchia (aka “Smiley”) has been immersed in the horse show world for 17 years. She rode and showed in Zone 2 as a junior, attended Centenary College in Hackettstown, NJ, and was the captain of the IHSA team. Nicole has groomed and ridden for several top professionals in the industry, including: Robin Rost Brown, Val Renihan, Missy Clark and John Brennan’s North Run, and Amanda Steege. She has spent a majority of that time traveling up and down the East Coast following the A-rated circuit, including Florida and all the indoor finals.
Nicole is also a frequent blogger for The Chronicle of the Horse. In addition, Nicole helped run a successful A-rated and C-rated horse show series in Augusta, NJ, from 2012-2017. Nicole has won four grooming awards in her career: at The Sussex County Farm and Horse Show (2013), The Capital Challenge Horse Show (2018), WEF (2018), and The National Horse Show (2019).
Nicole’s most memorable indoors’ experience was at The 2018 National Horse Show when both of the horses she was grooming claimed a tricolor in their respective divisions (Lafitte de Muze was champion in the Green 3’6″ Green Hunter division and Zara was reserve champion in the 3’6″ Green Conformation Hunter division). Nicole owns a Dalmatian named Maddie and her boyfriend Lee also works the horse show scene as an in-gate starter. Writing is a passion of hers and she enjoys sharing tips, funny stories, and advice on anything horse-related!