Trisseh
Duck-duck-chicken!
It’s very possible that it began as niacin deficiency and other problems came along for the ride, don’t beat yourself up at all. They grow so fast that even a couple of days make a difference in how to treat and what you’re treating. If you find that the tendon is slipped, you can try to extend the leg and slip it back into place but in a duckling that size I don’t know that it will stay put... what I did with my last one (he was only 3 days or so old) was extend the leg, slip the tendon back, and then wrapped the leg partly extended With vetrap so he couldn’t move it much. Since he was so small that only stayed on for one day. I gave him as much swimming time as I could as well to build up strength without too much strain on his legs throughout the process. When I removed the wrap his tendon was ok but he was basically splay legged at that point so he needed hobbles for a couple of days to get them underneath him. I’m not sure what the best option is for your little guy as he’s older and his legs are turned and pointing inward, but sturdy hobbles that don’t have a lot of “give” in the middle section to help separate and support his legs may be something you could try. Definitely only with supervision in a safe place of course.I looked into slipped tendon a few weeks ago but didn’t think it was that because it hadn’t progressed to this point yet and still looked much like Niacin deficiency. I’m now looking into slipped tendon and am thinking that it’s very much possible. He still eats and drinks plenty but he walks much less than the others so you’re likely right about him not getting enough for proper growth. With times being so hard at the moment with the virus I wanted to do what I could on my own with niacin supplementation and avoid the vet if possible, but now that i’m seeing the vet is my only option I wish I had just gone at the start :/ then again it looked so much like Niacin deficiency that if the vet didn’t have an expertise with ducks they may have thought the same
I do feel that not every “avian” vet is the right choice for poultry, either. If you have one that you like and it’s worked for you, awesome. I know personally in my area I definitely would not bring my birds to either of them that are here, as they don’t seem to understand that they are different than caged birds in many ways. Ideally you would have a food animal veterinarian that knows and treats poultry (and don’t just recommend to cull) but those are few and far between. Lol.