We would Not recommend rabbit pellets because of the high protein level which can cause "angel" wing in the swans. This is the same for wheat and barley. Use poultry layer pellets mixed with cracked corn. You can use the lettuce as a treat when you know that the swans will immediately eat the greenery prior to it freezing.

The cracked corn will act as a filler to keep them from being hungry. The poultry layer pellets will give them their much needed vitamins and minerals. The Regal Swan