As a mare enters estrus and prepares
for breeding, her levels of estrogen rise. After
she ovulates, estrogen drops and is replaced with
an increasing amount of progesterone. Progesterone
prepares her uterus for pregnancy and prevents
abortion of the fetus. Roughly 14 to 16 days after
ovulation, if the mare is not pregnant, her progesterone
levels decline and the cycle starts over.
Regu-Mate® is a synthetic form
of progesterone called progestin. When given daily
for up to 15 consecutive days, it reliably keeps
mares from entering estrus. When use of Regu-Mate
is discontinued, mares will return to estrus, or
come into heat, within 4 to 5 days.