I have a one year old Pekin Drake who has been limping forever it seems, no known cause. Today he wouldn't even try to walk, so for the millionth time I picked him up and looked at his feet... Then noticed his hock was really swollen. Tender. And hot. Ugh. Help!! I separated him and bought tylan 50 but unsure of dose etc. I had just special ordered brewers yeast as I was told niacin was needed for the limp. Suggestions?