Young mare with limb swelling during heat cycle

[Inimitable]

I have a coming 6yo unraced TB mare who has presented with something I’ve never seen before. At the beginning of March I noticed that she had some swelling in her limbs - mostly in her hinds, but I detected some filling in her front legs as well. Not much heat (maybe a tiny bit of ‘warmth’), not lame, eating, drinking and otherwise acting herself. It was not stocking up, she’s turned out in a herd 24/7 and plays pretty hard. Seemed to start/be worse in the left hind and then the right hind followed. I observed for a few days and the edema resolved completely. At the time I chalked it up to maybe something viral passing through the herd, or just random spring weirdness. From what I could tell it also coincided with her first spring heat.

4-5 days ago she came into heat again. And yesterday afternoon the mysterious swelling reappeared. Again in the left hind from her hock to her pastern, and it was starting to develop in her right hind, and a bit in her left front as well. This morning her left hind is FAT, there’s filling in her right hind, and some in her left front. Again no heat, not lame, appetite and attitude totally normal.

Some background: This mare has hard/uncomfortable heat cycles. She was at a trainer to get started last summer and was doing great. But every few weeks she would have a day or two where she would be explosive, you could not put leg on her without her balling up and threatening to launch you into the sun. I realized it corresponded to her cycles and learned to leave her alone during that time. She is not nasty in the slightest, she is the sweetest mare on earth - but she clearly gets painful for a few days during her cycle. Otherwise, she has been very sound (other than the occasional footiness on very hard ground), no injuries, etc. She is built like a brickhouse.

Any thoughts on this swelling corresponding to her heat cycles? Is this a fairly common thing that I’ve just never encountered until now (eg. water retention)? Or am I connecting dots that aren’t meant to be connected? It’s weird!

[GraceLikeRain]

I’ve definitely never heard of that but horses love to be unique. Would trying regumate be an option to see if moderated her cycle improved the episodic swelling?

[Inimitable]

I would definitely consider regumate down the line if the episodic swelling persists and the pattern holds up. I’m not ready to go there quite yet. They are all due for their spring tune ups soon, so I’m going to try and schedule the vet to coincide with her next heat to see if we can catch it in person. Some more background: this mare was a rescue. I got her as a 3yo and she was pretty undernourished/neglected from the time of her birth and therefore a bit late-blooming. I’m hoping her cycles will regulate/moderate on their own as she matures.