One of my mares has never showed classic signs of being in heat (like squirting), but as she got older (starting around 4/5), more often than not, she would be very reactive to silly things and would also explode randomly. We’d be trotting nicely down the long side, happy, soft, stretching, and then BAM we were galloping in the opposite direction. The constant spooking over silly things made it pretty challenging to accomplish much under saddle. We could go by the corner where she thought there was a monster 20 times and she still wouldn’t be convinced. She was also hyper-reactive around the barn, in turnout, etc.
We ruled out everything we could think of – lameness workups, custom saddle, scoped clean as a whistle, plenty more. I was reluctant to try hormones (particularly because her behavior issues didn’t ebb and flow as much as I thought they should if the problem was hormones, though they did some), but eventually we tried Depo, and that helped quite a bit. A year or two later we gave regumate a try. The regumate completely eliminated all of the spooking, spinning, hyper-reactiveness. Now a kid can do all of her handling or even climb on to tootle around. A deer in the woods can leap across our path and she’s just like, oh hey buddy. It was kind of a miracle for my mare. (I’m sure it didn’t hurt that she kept getting older around this same time!)
Now anytime she is going to be in work, she goes on regumate.