We will need to defer this diagnosis to your local avian veterinarian as far as proper diagnosis and treatment. The poultry pellets provide the swans with the necessary vitamins, minerals and other nutrients while the corn is just a filler. Swans will eat whole corn, but cracked corn seems to be more easily digested.

Again, without seeing the birds walk, etc, it would be very difficult to render a diagnosis especially just looking at possible photos. Although most veterinarians do not have experience with swans, if you can find an avian veterinarian in the area who works with waterfowl or poultry, he/she may be able to help you with this problem. If the bird just walks funny, but is able to walk and you can provide it with the proper nourishment (which may or may not be too late to change the course of the condition), then further treatment may not be necessary. But, again, you need to get the bird to an avian veterinarian. The Regal Swan