Hi, I was just checking this site out to see what I could learn, and to my surprise the first post I see is one I can (semi) answer! So I am now a member.
I can't give you the value or anything specifically about Kendall's, but I am pretty sure it was an old linament used on horses to treat bone or bog spavin, which is swelling in the hock joint that can lead to lameness. Unfortunately the linament probably wasn't very effective because these days we know that a spavin is just a symptom of some other problem like poor conformation and is mainly treated with hydrocortisone injections. But people used to use linaments like we use body lotion!
So if you are trying to sell it, I would check out the veterinary antique market for more value related answers.
