No similar experiences. It could be several different things, but I'm sure the vet will help figure things out tomorrow I'd ice for 15min on/off while your waiting for the vet to try and reduce inflammation or cold hose for 20min. Voltaren double strength, which you can buy at the drug store might also help you for today. Personally, I'm not a big fan of Bute unless It is absolutely necessary for pain or chronic inflammation or the Vet suggests It to be used. It is hard on a horse's stomach, liver, actually slows healing. If you do use It though, be sure to inform your vet on how much and when you used It. I hope everything goes well for you tomorrow I'd love to hear the vets diagnosis If you share.
Yeah sounds like he's probably bashed it badly on something. I'd do cold hosing & anti inflams... Interesting for the Voltaren suggestion @Jolly101 - been meaning to look up doses for my dog of human stuff before she needs it, of meloxicam, as I get proscriptions for me & know it's the same drug(but vastly dearer) for dogs & horses, and this one is meant to be more effective, longer lasting & safer on the gut than voltaren, according to my doctor.
I'd probably give it a few days before calling the vet, so long as it doesn't get worse, but if not getting any better by then I probably wouldn't leave it much longer.
Voltaren gel is an RX applied topically, from personal experience, useless stuff. Meloxicam and all the NSAIDS cause ulcers and are best avoided if possible. Ditto the cold hosing & icing until the horse can be seen by a vet. If you have swelling & warmth in the joint, I'd call the vet out if for nothing else, than the horse's age. 24 gets the vet consolation prize just for being a long lived member of the family.