A lot of us have posted our observations about our EPSM horses getting odd swellings in the udder or sheath, and around the head when they're having muscle issues. Tink's having a bit of a bad spell with the spring grass, and the swelling has returned, and I wondered if any explanation for it has been discovered yet.

Other than possibly reduced muscle activity causing reduced circulation in the area, no, there are no hard and fast explanations for this yet. I hope Tink gets over this quickly, though.

I asked the barn owner to turn Tink out on grass muzzled in the morning only, and she's recovering nicely! That swelling is such a mystery, though. At one time her jowls and around her eyes swelled up so much her halter didn't fit. It seems like a lymph-type thing, but who knows.

The head swelling syndrome has been recognized in hores from some parts of the US and also in the UK. No one really knows what the cause is, but it is suspected that something associated with spring pasture plants (perhaps a fungus???) causes this facial swelling. When horses are kept off the pasture the swelling goes away, just as you describe. This doesn't usually involve udder or sheath swelling, though. Whatever the cause, the grazing muzzle is a great solution and I'm glad to hear that Tink is recovering.