i agree with @betsygee . also, i don't think the possible excess Vitamin D is related to the rectum/anus issue. make sure to feed a wet-only diet. if your cat had excess Vitamin D, the signs/symptoms would be: vomiting, weakness, depression, lack of appetite, increased thirst and urination...
"The feeder features a weighted sunscreen at the opening of the feeder that allows cats and small dogs to eat, but keeps out most birds."
http://www.outdoorpetfeeder.com/index.html