>Dogs cn survive on a vegetarian diet, if it's suplemented with vitamins.<
They might survive, but they sure don't thrive. Not only that, if you stick a piece of liver and a piece of bread down in front of a dog, you better not be between him and the liver!
Interesting thing about the change in dietary habits. Liver used to be the choice delicacy...now it's the food few would eat willingly. I suspect it has a lot to do with nutritional cravings. People have no need for the concentrations of fats and things that would drive them to crave something so icky.