I brought Red in during the afternoon yesterday and put him on the lunge - sound at trot in both directions! So I rode briefly, mostly at walk. We did try a little trot, and he was happy about that, although when I lunged him again very briefly afterwards he was slightly short striding with the left hind when tracking right, but nowhere near as much as he had been several days before.
While I was groomed, I noticed that his left hind hock (same leg) seemed just a little bit swollen - it was hard to see but there. He had a new small cut on the outside of the hock - it looked like he had received a glancing kick blow. He already had a couple of other nicks and scrapes on that hind leg - looks like he's been mixing it up in the herd, probably to climb in status - he's been at the barn for about two weeks now so he's got the lay of the land and may be ready to make some moves.
This morning when I went to bring him in to ice his leg, his hock was very swollen - it looked like a melon, and the swelling had also moved down into his lower leg due to gravity. It didn't seem too sensitive to the touch and he was walking well. A sudden increase in swelling like this is always a cause for immediate concern. Just by chance, our vet happened to be at the barn doing x-rays of another horse, so I was able to get her to look at him right away. She said it looked like the joint was OK, but that he'd started an infection due to bacteria getting through the skin from one or more of the little cuts and nicks - effectively, he has cellulitis.
So we're on a banamine and SMZ antibiotic routine. I'm to keep a very close eye on things, and if I don't see improvement within a day, we may need to switch antibiotics. He's to have 14 SMZ tablets twice a day, and amazingly enough when I put them in his food dish he just ate them! He doesn't get treats ordinarily, so perhaps he thought they were some sort of very odd tasting horse treat - he was making faces as he crunched them up. I hope he keeps eating them - I put some in his feed for this evening - if not we can always resort to pasting, although that's no fun and a big mess. I've also started him on some probiotics to fend off ill effects on his digestive system from the antibiotics.
Poor Red - he really likes to work and likes the attention that involves - he'll actually bang on his stall door to let me know that he wants to come out and do something together with me (even though I always ignore him when he does that and take him out later) - once we do something together, he's happy and just eats his hay. I'll have to come up with some fun non-riding things for us to do together as he heals. But considering the super hot weather we're about to get, that was probably going to be needed anyway.