What can I use to help a horse that has a swollen tendon in off side leg??
Swelling in the tendon could be caused by a few things ranging from infection to a strain. I would recommend consulting with your veterinarian for advice to ensure the correct diagnosis is reached and appropriate treatment is started.
One product that may help, depending on the underlying cause, is Swelldown Poultice which can be applied to the leg to help reduce inflammation and swelling.