I usually recommend 1/2 tablet of super B complex or just B complex. They have plenty (about 20mg) of riboflavin and all other B vitamins, and some C. Riboflavin tablets have tablet 200 mg in them, but you can use those if you just scrape a little into food or a treat every day. Hopefully, the...
Is there any way that you could upload a video to YouTube with a link posted here, of him walking around, showing his legs. Do his legs appear straight, or is there any bowing out or in of either leg? Does he walk or sit on his hocks? Have you tried giving him any human B complex vitamins?