My two back swans have stopped eating the mix I have been giving them for years. There has never been a problem with this before. They also have access to a lawn, wooded area, so get a varied diet. A problem I now have is that I deworm them with a mix in their feed, must I now attempt this aurally? Part of my trepidation comes from the increased aggressive behaviour of my male swan, normally reserved for periods when the female is on the nest, and now continuous. Their general behaviour is out of sorts the last few months. Any ideas ?