[Christian Science Monitor - opinion - comments at full story link]

Q: I don’t eat meat, for a variety of ethical and environmental reasons, and I’d rather not feed it to my cat, either. Do cats have to be carnivores?
       – John McManus, Needham, Mass.

A: Unlike dogs and other omnivores, cats are true (so-called "obligate") carnivores: They meet their nutritional needs by consuming other animals and have a higher protein requirement than many other mammals. Researchers state that cats get certain key nutrients from meat that can’t be sufficiently obtained from plant-based foods. Without a steady supply of these nutrients, they say, cats’ health can suffer.

A cat’s ideal diet is made up mainly of protein and fats derived from small prey such as rodents, birds, small reptiles, and amphibians. Some cats munch on grass or other plants, but most biologists agree that such roughage serves only as a digestive aid and provides little – if any – nutritional value.

Providing your domestic cat with a steady stream of its preferred prey is hardly convenient or humane – and cats can and do wreak havoc on local wildlife populations if left to forage on their own. So we fill them up on dry "kibble," which combines animal products with vegetable-based starches, and meat-based canned "wet" foods, many containing parts of animals that cats would probably never encounter, much less hunt, in a purely natural situation. Most cats adapt to such diets, but it is far from ideal nutritionally.

Veterinarian Marla McGeorge, a cat specialist at Best Friends Veterinary Medical Center in Portland, Ore., says that the problem with forcing your cat to be vegetarian or vegan is that such diets fail to provide for proper feline health and are too high in carbohydrates that felines have not evolved to be able to process. As for powder-based supplements intended to bridge the nutritional gap, Dr. McGeorge says that such formulations may not be as easily absorbed by cats.

Some vehemently disagree. Evolution Diet, makers of all-vegetarian foods for cats, dogs, and ferrets, says that its meatless offerings, on the market for 15 years, are healthy and nutritious. If anything, their products have extended the lives of many felines and canines, they say.

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full story:

http://features.csmonitor.com/environment/2009/03/13/earthtalk-can-my-cat-be-a-vegetarian-too/