Pekins can develop leg issues it can be from niacin deficiency, an being over weight. At 4 months old he’s at the age where he’s becoming an adult. If he has had niacin supplement since tiny they can actually still have one even though on a supplement. So ducks just seem to need more. That’s when the liquid b complex comes in. If a niacin deficiency it can turn it around if caught before the duck is too far crippled. Did we give you the info on niacin deficiency? Keep info them from getting over weight is crucial since weight on legs already weak can really make them worse. Feeding a good quality feed and keeping treats to a minimum is important. Treats should only be 10% of daily feed intake. Good healthy treats too we have a list if you don’t have it. https://www.backyardchickens.com/th...cy-in-waterfowl.1367557/page-11#post-23016501. https://www.backyardchickens.com/threads/the-ultimate-list-of-duck-treats-and-supplements.242460/