There are plenty of things that could be causing swelling in your horse’s legs: Ligament or tendon injuries, bruising, splints (bony enlargements of the bone in your horse’s leg), arthritis and other things like that. These swellings may be hot to the touch, hard or soft, and your horse may be lame. If you see swellings like this on your horse, you should call your vet before it gets any worse.
