We're still not sure about the rabbit pellets. If this is something that you have been feeding the swans and you have had no problem with angel wing, then we see no reason for you to stop using the product.
Secondly, all grains such as wheat, barley and even alfalfa have to be closely scrutinized due to the possibility of having red clover intermixed in the greenery which can severely sicken or kill the birds. The Regal Swan « Hide