Yes. many do. This is a reality of nature we have to either work through or ignore. I had a vegetarian friend once who raised his cat without meat, but treated him like a king - cream, not milk, for Rudi, who had his name painted on his own wicker chair, and got home-made custard for breakfast on Sundays. He didn't look unhappy and grew large and strong. I've heard of dogs being fed ovo-lacto vegetarian diets, as well. When you read the labels on pet-food, they're mostly cereal anyway. The very expensive ones advertise that they use rice instead of corn- that is better, actually, and add beet pulp or peas or something equally unnecessary. Or even ground peanut shells, for fiber. Want to pay extra for peanut shells? Some of us simply accept that, unlike us, with our unlimited choice of foods, our pet is an obligate carnivore. Most domestic cats are not good enough at hunting to sustain themselves, or have no rodents in their house, and their humans frown on and all-songbird diet (not enough nourishment in a sparrow or chickadee, anyway, to offset much more than the energy required to catch and subdue it). So I buy kibble (mostly corn, soybeans and chicken-beaks) canned food (mostly grains and chicken skin and gristle) and sometimes an actual chicken or turkey, which i cook and debone and mix with yeast, vitamins, calcium, wheat germ and cooked barley. Did you know cats can eat around a grain of barley, leaving it perfectly intact and clean? Now i grind it up.