I can tell you the story of my mare
that acted just the same. It began when I sent her to my trainer's, this
spring, for some trailriding training. (She has been a broodmare) Beeper was so
bad that my trainer couldn't ride her on the trail with any other
horse. She would just stop, squat, pee, and stand for ANY horse. The
vet did many tests, said possibly cancer in the ovaries, did blood work,
ultrasound, internal palpitation, etc. He did discover one of her ovaries
is small and hard and apparently not functioning, but no cancer. He
gave her a shot of a hormone that he had compounded for race horses he
vets. That helped but not completely. Finally he inserted a
sterilized marble into her uterus. Beeper is a 9 year-old Tenn.
Walker that has already had three foals (her last colt is a yearling now)
and she didn't exhibit signs like this until this year. So far the marble
has stopped her heats and she is back to normal acting. I don't plan to
breed her again, so I can leave the marble indefinitely....I believe.