Progesterone is a useful hormone in mares and has been used for:

• suppressing estrus (heat) in mares
• normalizing erratic cycling in mares during the transitional periods
• timing ovulation and breeding in mares
• maintenance of pregnancy following septic conditions
• and controversially, maintenance of early pregnancy do to low progesterone levels

Progesterone and related natural hormones are released from the corpus luteum on the ovary and from certain structures of the placenta. Hormones with progesterone-like activity are called progestanes. Regumate® is a man made progestane, altrenogest, that has strong progesterone properties and can be placed in the feed. The proper use of progesterone and Regumate® requires understanding the hormones actions. This article discusses the actions of these hormones and their use in equine medicine and reproduction.

Before spending hundreds of dollars on Regumate® to prevent early embryonic loss, we recommend you read this article.

Progestanes help the uterus prepare for pregnancy and inhibits the onset of estral hormonal events thus preventing a mare from coming into heat. When a mare is put on progesterone she continues to cycle up to the point of heat then stops. A cycling mare on progesterone for 14 day then taken off the hormone will return to heat in 3 days and most mares ovulate between 8-15 days after withdrawal.