If you ask any canine they will probably tell you there is no such
thing as bad dog food, but the reality is that many of the cheaper
brands are not that good for them. Some of the lesser-known brands
have been known to use ingredients that may not be the best for them,
including beef from sick or dying cows as well as other animals that
may not be in the best of health.
Additionally, not all dog food is created equal and it may not contain
the vitamins and minerals dogs need for health, and animals at
different stages of their growth need different supplements and even
if made with healthy ingredients it may be bad dog food if it does not
have what your dog needs. There are certain things the dog will need
for its health, but there are also certain foods that are healthy for
humans, but can be deadly for dogs.
For example, apples are considered a health food for people, but for
dogs apple seeds contain cyanogenic glycosides, which can result in
cyanide poisoning in canines. The same thing can happen with apricots
and cherries making these fruits extremely bad dog food....

http://groups.google.com/group/dogfoodmave