Can someone please tell me what problems, if any, may occur when mating a gander with it's daughters and subsequently their daughters. I've been told that waterfowl can inbreed successfully for six generations or more, but personally I'm a little sceptical.
Any information, factual or anecdotal, would be well received.

In ducks I have had any inbreeding result in bad legs and other undesired traits. I would recommend possibly getting another gander from a different bloodline, that way you can keep a fresh gene pool and cross the offspring back.