Older lame duck - what could be the reason?

[pond]

I have an older duck called Brownie. She is about 8 or 9 years old. More than a year ago she started limping. It was getting worse. I checked her feet but there was nothing out of ordinary there. It got so bad she could hardly walk. I looked online and found that it could be caused by deficiency in niacin. I bought brewer's yeast and have been adding it to her feed every day since then. She improved at first a bit but is still having really hard time walking. I'm feeding my ducks purina organic baby chick starter grower, because of extra protein. I've been also adding either meat or fish to their feed for months now. The other ducks also get sprouted sunflower seeds and are roaming my backyard for bugs. Brownie doesn't move much if she doesn't have to. I don't see any improvement with her, she is not getting worse either. She stays the same. Any ideas what's causing this and if there is anything else I can do? Here is a glimpse at her walking ability:

 

[chickens really]

Arthritis possibly?

 

[Miss Lydia]

I had a Muscovy drake that at the same age as your mBrownie he was probably 9 ish. His legs gave out on him I figured arthritis so I started him on glucosamine it really never helped him. He ate drank and enjoyed his girls just could barely get around. I carried him around to the front yard in the morning with his females and kept a gate closed so the other Drake’s wouldn’t pick on him then in the evening I’d carry him to his bed. He could still walk but it was hard for him like your Brownie. He still enjoyed life until he was 1 month shy of 12 yrs old he just gave up. He was my first duck I was happy to take care of him. Ernie was in a smaller area so he didn’t over do and injure his legs. You might try a inflammatory drug with Brownie you’d most likely have to go through a vet.

 

[pond]

Thank you both, and specifically for the story Miss Lydia. I sometimes carry Brownie out or back into the coop, though she does not like it. She got used to it though. I can't believe ducks would get arthritis and so early too. 9 years old is not that much for a duck from my understanding. Too much carbs in their feed I reckon. I guess there's nothing that can cure it at this point... :-(

 

[Miss Lydia]

Trying an drug for inflammation or for pain might help. That is pretty old for a duck I think, there maybe some that live up into their teens but probably not many. I think the fact that their legs aren’t that strong may have something to do with it I have a 10 yr old Muscovy female that has a limp I can only guess it’s arthritis since there isn’t anything on the outside telling me different . She is still enjoying life that to me is the main thing.