I asked the BO and the vet, and they both thought that it was from the 2nd cutting of grass hay he was getting...which the BO said makes horses retain water like salt does to humans.
She also mentioned that it could be that he has a slight infection since he has some scrape marks on his back legs, and he possibly peed on his legs, causing the infection. Those scrapes have been there on his leg since I got him, so I don't fully understand how that could cause it, but I see how it could I guess.
I scrubbed his two back legs down with Betadine solution mixed with water, then let it sit for 10-20 minutes, then washed it off. The BO said she'd check on him tonight, and if the swelling has not gone down at all she'll give him one tablet of bute.
We did go out on a trail ride yesterday, but nothing severe or anything like that.
Any ideas on what could have caused this? Do you think it could be the hay? The only two horses that I saw with their legs that swollen was one that got cut and it for infected...and the other got kicked there.
No pictures, camera died on me :(