12 isn't even middle aged for an Arabian!! A friend of mine retired her Arabian gelding from showing at 26, and not because of his health, but because he'd won everything already, lol.
If he's doing that poorly, that suddenly, then you need to have your vet out NOW. Have blood work done, maybe x-rays, and an overall thorough exam. Arthritis isn't the only cause of painful joints.
If it is arthritis, then this is one more example of why young horses should NOT be ridden until 3-4 and not ridden heavily or competed until after their 5yr old year is done. Hocks aren't closed until 4.5-5.5 yrs old, and all the bones are closed/matured until 6-7 yrs old.
Last edited by luvs2ride1979; 03-26-2009 at 12:58 AM.