The following information can be found here:
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Anemia (Iron Deficiency) Anemia is charachterized by loss of color in the Caruncles(red mask around the face). If a Muscovy Ducks is anemic, it's caruncles will become pale & in extreme cases, orange in color. Muscovies that are not on proper diets or allowed to free range are most succeptable to this condition. This problem is easily corrected by allowing the bird(s) to free range, feeding greens & acceptable scraps as often as possible. Wet dog/cat food can also be given to birds suffering from anemia.
Foamy Eye Foamy Eye is just what it sounds like, excessive foaming in the ducks eye. This problem is more common in Drakes, probably due to them having more caruncling than hens, but there's no way to really be sure. It is most commonly caused by lack of bathing & injury to the eye but it can also be brought on by stress & sudden changes in the weather. It is more common in Winter because some ducks bathe less or have less access to bath water during that time. Foamy eye is usually easily fixed by providing clean bath water for the bird(s) & making sure they bathe well.
In some cases, Foamy Eye can be a sign of underlying Illness or Disease. If the bird is not having any other obvious problems such as wheezing, runny nose, coughing or being lethargic then there is probably no cause for concern.
Wet Feather is a condition commonly charachterized by "raggedy" or "torn-up"-looking feathers and also an inability to repel water. Wet Feather is one of the most common problems I have seen & experienced with Muscovy Ducks. It is easily fixable by providing the birds with plenty of clean water to bathe in and a clean, dry living area. Black Oil Sunflower Seeds(BOSS) are also a very good supplement to help restore oil production & make the feathers healthier & more waterproof.