I have used Wysong's F-Biotic as a topper and my Boo LOVES it. Unfortunately, I determined later that he has a possible allergy to both poultry and yeast (brewer's, nutritional, etc.), so I am no longer able to use this as a topper.
Has anyone ever tried any of the Wysong supplements? You could use them as toppers - http://wysong.net/cat-dog-supplements.php I was thinking about trying the Cheezyme one - anyone have any feedback on those?