i have had miraculous luck with Colloidal Silver and animals. i suggest have a maker around just for tham if not for emergency flu and cold use. plus, it is good for wounds and burns.
go to the CS forum for lots of info. if you want to try it, just get a small bottle of ionic silver at the health food store. dont get the proteins. i think sovereign silver is the brand i have heard recommended most. i have never bought but make my own. you can pour it directly into their water dish. i would use distilled water and only give enough to drink for one day, so they drink it all. buying is is a little spendy.