We had free range Muscovies for MANY years and never, ever had a problem with their health & so far I have had no problems with my Grain-fed Muscovies(or other ducks), WITH the exception of Sidneys brief walking problem. ( ) I've recently seen lots of stuff about Niacin levels & bumblefoot and other issues with ducks. What are the Pros/Cons of Free Ranging & Grain feeding(penned up birds)??? My Muscovies are currently penned & free ranging nearly everyday on our large property, with access to a large creek & mucky, duck heaven, pond. So they eat penty of bugs, grass, greens & probably, currently, LOTS of Salmon eggs!! They also only drink natural spring water & creek water (same).