I had an oak tree in our backyard when I lived in Illinois and our dogs would eat the acorns. They became sick to their stomachs with vomiting, runny stools, etc but it was never fatal, so when you posted I did some research and found that yes indeed acorns can cause kidney failure but not sudden and not without showing gastrointestinal problems first. Acorns contain gallotannin which, depending on the amount eaten, can cause gastrointestinal upsets in pets and other animals, with symptoms such as cramps, vomiting, constipation, diarrhea, sometimes bloody diarrhea, and kidney failure. A few dogs may have seizures. Acorns swallowed whole have the potential to block the intestines, while chewed acorns release more toxin and the sharp pieces can irritate the gastrointestinal tract.
I suggest you read this article
http://dog-care.suite101.com/article.cfm/dangers_of_dogs_eating_acorns


