Hi
@Kitkat1992
Thanks for posting the video. That gait is strange and hopefully someone here will have seen it before and will know its significance. If not, it might be worth seeing a vet or consulting an online duck vet. The online option is much cheaper but I dont know how reliable it is.
In general, I have found that stopping walking is a common but non-specific response in ducks. Speaking as a person who had a duck stop walking over 3 days in May, that has still not recovered, this is what I have found from research -- on line and from talking to duck keepers, and wildlife rehabbers.
1. A duck may stop walking as a result of trauma, infection, toxins, or nutritional deficiency.
2. The most common reasons are i. bumblefoot, or infected cut on a foot, and ii. niacin deficiency. Hence the advice that you give niacin to your duck. It's important to give a trial of niacin therapy and not assume your duck is getting enough from her feed.
Individual ducks vary in their niacin requirements and while commercial duck food contains adequate niacin for most ducks, there are outliers who need more than provided in duck food. Most commonly rapidly growing pekin ducklings and laying jumbo pekins need a niacin supplement to their diet.
Have you had a good look at your duck's feet -- particularly the underneath of her right foot? Is there any sign of a cut or early bumble?
3. If there is no foot problem or niacin deficiency, the remaining causes of stopping walking -- ingestion of toxins and systemic infections, such as West Nile Virus -- are difficult to diagnose without the benefit of a vet or blood tests.
Many duck keepers try treating with activated charcoal to remove toxins (from botulism or metals etc) 'in case' the duck has ingested a toxin. Apart from this, one can only provide TLC to a duck that has stopped walking. Tender loving care includes putting the duck in deep water to swim (a kiddie pool is not deep enough, but a bath or a plastic tote can be filled deeper so the duck needs to move its legs and cannot just sit on the bottom); keeping the duck clean as it will sit in its poop (I find sitting on puppy pads the easiest way to manage that) and keeping the duck safe, generally in or close to the house. But that depends on individual set ups. Ducks do not like to be isolated, so keeping a non-walking duck in close proximity to its flock or a buddy from the flock is important.
4. I just learnt, from a wildlife rehabber, of another nutritional deficiency that can cause a duck to stop walking. She recently had a female duck that was brought in because it had stopped walking. She was out of wild duck food and fed the duck layer crumbles. That duck started walking again in 5 days. The wildlife rehabber thinks the duck was developing calcium deficiency, that was remedied by the calcium in layer crumbles.
In sum, I don't know why your duck has that particular gait. Nor do I know why your other duck stopped walking and died. But as summarized above it is quite common and we can't always know why
