Lexington, Ky. – As of December 1, 2024, the use of any progestogens in stallions and geldings while competing in USEF licensed competitions will be considered prohibited under Chapter 4 of the USEF rulebook.

Altrenogest, known as Regu-Mate® commercially, 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 ,” stated US Equestrian Chief Veterinary Officer, Dr. Stephen Schumacher. 

While alternatives exist for males (gelding), surgical removal of the ovaries is not as easily accomplished as in other species. Altrenogest provides a means to normalize mares during estrus.

Altrenogest will continue to be permitted to be used in mares under Federation rules.