Although she's heard anecdotally of healthy vegan cats, she said she suspects that those cats may be supplementing their meat-free diets on their own.
"If they're not getting meat, they're probably going to try to hunt -- maybe for the mouse in the house or the bird in the yard," she said.
But pet owners like Moore and the manufacturers of vegan pet food maintain that most veterinarians don't have enough training in nutrition.
"Here's the reality: We've been doing this for 20 years. We have dogs over 19 years old in good health. We have cats over 22 years in good health," said Eric Weisman, CEO of Evolution Diet Pet Food Corp., a manufacturer of vegan cat and dog food.
Weisman said thousands of clients across the United States, including animal shelters, use his vegan pet foods with success.
Although it's true that the amino acid taurine and other proteins are necessary for cats and dogs, he said that synthetics can be added as substitutes.
"Our food is 100 percent complete according to state requirements," Weisman said. "We have all the proteins and all the fatty acids found in meat-based [foods] but without the cruelty and destruction of the environment."
Like many vegans, Moore said she chose her diet because she cares deeply about animals and wanted to "live [her] ethics." For her, extending veganism to her cats supports that choice and also helps reduce her environmental footprint.
"Just converting plants to animal protein is outrageously unsustainable. Anything we can do to reduce that makes life a little better for everybody," she said. Moore also said that she and her partner started a social network for vegan cat owners to help support others with similar beliefs.
Although he doesn't yet have the data to prove it, Jason Clay, a senior vice president for the World Wildlife Fund, said he suspects that, in its lifetime, the average cat in the United States and Europe has a larger environmental footprint than the average African.
Regardless, some think that there are other ways to live out one's beliefs and support the environment.
Christie Keith, the lead science writer for petconnection.com and a pet columnist for the San Francisco Chronicle, said pet owners concerned about their environmental impact can buy organic and sustainable pet foods or make home-made meals for their pets.
"You can get anything you want for pets now commercially or you can make it," she said.
Acquiring pets that naturally eat only plants is also another option.
"Overall, what I would say is when we turn wild animals into forage, I think it's an overall disrespectful thing to do. It's one thing to kill an animal for human consumption. It's another to grind it up and turn it into feed," said Paul Greenberg, an author of a forthcoming book on the future of fish who recently wrote a New York Times op-ed about the impact of the pet food industry on the world's fish stocks.
The use of wild fish in animal food causes significant problems for the world's food systems, he said.
But Greenberg does not support turning a carnivorous pet into a vegetarian pet.
"A carnivore is a carnivore," he said.
If anything, he favors looking down the food chain in considering a pet.
"A carnivore, be it a cat, a dog or a salmon, is a heavy burden for the environment and should not be brought under human care lightly," he wrote in his Times op-ed. "To me, a vegetarian substitute is seeming more and more appealing. Lately, I've had my eye on a guinea pig."