The U.S. Equestrian Federation has announced that as of Dec. 1, the use of progestogens in stallions and geldings while competing at USEF-licensed competitions will be prohibited under Chapter 4, Drugs and Medications, of the USEF rulebook. Progestogens are still permitted in mares.

Altregonest, commercially known as Regu-Mate, is the FDA-approved synthetic progestogen commonly administered to mares to suppress estrus and associated seasonal behaviors in competing horses, and to aid in breeding practices with broodmares.

“There is no legitimate therapeutic use for progestogens in stallions and geldings while competing,” USEF Chief Veterinary Officer Dr. Stephen Schumacher said in a press release. 

The rule change follows a Fédération Equestre Internationale rule that has been in place since 2011, which only allows altrenogest to be used in mares to prevent its misuse as a calming substance.

“Altrenogest and MPA [Medroxyprogesterone acetate, more commonly known as Depo-Provera] have the possibility to be misused as a calmative, especially if used on stallions and geldings, affecting performance and therefore contrary to FEI rules on clean sport,” an FEI spokesperson told the Chronicle in 2017, when USEF announced it was going to examine the rules on both substances.

In September of that year, the USEF board of directors voted to approve a recommendation to require an MPA disclosure form for any horse receiving MPA while competing. But after Depo-Provera was linked to anaphylaxis and fatalities, USEF banned its use in competing horses starting Dec. 1, 2019. At the time, no change was made to the permitted use of altrenogest.