It's actually called Penis Paralysis, or Phallus prostration. Here is a paragraph from Barnyard in your Backyard (a book) about it:
"Penis paralysis is a sad result of domestication of waterfowl. Under natural conditions, ducks and geese breed at maturity and have a short breeding season. At other times of the year, they are busy with more important things, such as migrating and finding enough to eat. Domesticated waterfowl, on the other hand, are required to do little to sustain themselves. They start breeding at a younger age, the males are often expected to breed more females than they would under natural conditions, and they breed for a longer period. As a result, sometimes a drake or gander overexerts his male organ to the point that he can't put it away anymore. It bounces around behind him in the dirt and mud, while the drake or gander wags his tail, hoping to get it to go back in. Eventually it becomes dirty and scabby, dries out, and perhaps gets infected, and the drake or gander may lose weight or die. This conditions may be a genetically inherited weakness of the muscles, possibly aggravated by some dietary deficiency. Usually, by the time the condition is noticed, nothing can be done but to put the drake or gander out of his misery."
I'm so sorry....:(