My dad's horse was notorious for getting abcesses, and most of the time the only symptom is he would all of a sudden be sore. My mare though, I was able to finally get on her after a week off because she pulled the tendon around her knee, and she managed to take off for just 3 strides, but nothing happened. Finished walking her around, then hosed her off, and put her away. Her leg felt fine, and she looked content and happy so I left. Next day I came out, and she was pretty much non weight bearing on her front leg, wouldn't move, and there was no heat or swelling that I could see, not that she would let me touch her leg much. Called the vet out since it was so bad, and found out she almost severed the superficial flexor tendon. Not one of my better days. It only swelled up after I took off the pillow wrap, pressure wrap, and cast the vet put on, just to replace it with a pressure wrap. But it was quite obvious that she wasn't going to be moving anytime soon, and she was completely miserable. In your case I'd really guess abscess especially if it's been a wet season. Keep us updated.