Our pets can be hard on the environment. "They can have a big impact, especially when you consider that there are about 175 million dogs and cats in the U.S.," says Katherine Miller, an animal behaviorist for the American Society for the Prevention of Cruelty to Animals. Here are a few ways to help your pet be kinder to the planet.

Take in a pet from a shelter and you'll save it from being one of the more than three million cats and dogs euthanized each year, and reduce the resources used in shelters. If you long for a particular type of dog or cat, check out Adopt-a-Pet.com or breed-rescue organizations.

When you spay or neuter your pet, you may conserve future food, money, and energy. You're also heading off "the trauma and neglect that most unwanted animals experience before landing in a safe place," says Melinda Miller, hospital director of Smith Ridge Veterinary Center in South Salem, New York.

The best pet foods are meat based, and meat production takes up precious agricultural land. Try to compensate for this by using minimally processed foods that contain meat from locally raised animals and organic vegetables. If you have the time and interest, you can make simple, fresh food and eliminate packaging. Just be sure to feed your pet the right balance of nutrients (ask your vet for advice).

Pet poop is a problem. "Fecal bacteria can sicken other animals and contaminate ponds and lakes," Melinda Miller says. U.S. landfills overflow with nonbiodegradable bags containing dog waste and kitty litter. Dust from regular kitty litter can even be carcinogenic. Look for biodegradable litter made from recycled materials. Use biodegradable bags (available from Martha Stewart Pets at PetSmart.com) to dispose of your dog's waste, as well as kitty litter.

Green pet gear is becoming increasingly popular; you can easily find appealing products made from organic or recycled materials. Close to home, you can recycle crafts supplies for toys -- cats love playing with scrap yarn and fabric. Avoid plastic and products containing bisphenol-A or phthalates.

Don't discard gently used pet gear -- check with your shelter to find out whether it can put your castoffs to use. Many shelters have a food bank, and by giving unopened bags and canned pet food you can help people feed their animals in hard times.

Look for gentle, chemical-free pet shampoos and conditioners. To be safe, choose high-quality brands; when in doubt, consult your vet.

Every day our pets are exposed to objects and surfaces containing chemicals. In the house, use green or homemade cleansers, such as diluted vinegar or baking soda. For pet stains and odors, enzyme-based products, such as Petastic and Nature's Miracle, work well. Outside, opt for pet-friendly sprays and oils instead of harsh pesticides.