Ok so I went on a search to find out if swans can be fed poultry feed. The general consensus of the breeders was pretty negative. Almost every one of them recommended the Mazuri Waterfowl. However I did express the cost of feeding Mazuri and the breeders also said they use whole wheat, oats, and whole alfalfa to cut the Mazuri and reduce cost. Now mind you these are breeders and most of these did not have a large free range area or had a lot of swans that couldn't be supported by the environment they were kept in so they had to be supplemented with feed. So Mazuri was what they recommended but then with the wheat and oats and alfalfa. They also said you can feed them greens and clover clippings as well as some lettuces like romaine and leaf and also vegetable leavings like peelings and such from your dinner scraps.
There was one place that feeds theirs poultry pellets mixed with corn and wheat but their birds spent a majority foraging for their own food in a lake.
