Can cats eat grass outside?

Q: Milo—our cat—often accompanies us while we relax on the porch on cool evenings. Sometimes, he goes into the yard and eats grass. Why do cats eat grass?

A: As carnivores, cats eat herbivores like mice and voles. Since these herbivores eat grass, the free-roaming cat ingests any grass inside its prey's stomach and intestines.

Grass provides the cat with roughage, which helps move hair ingested during grooming along the gastrointestinal tract. Besides, some cats seem to like the taste and texture of grass, much as some of us humans enjoy a salad with our meat.

Eating yard grass, though, is a problem for two reasons: toxins and parasites.

• If you treat your grass for weeds or insects, the herbicides and pesticides may sicken Milo.

• Any stray cats that defecated on your lawn may have deposited parasites that Milo will ingest with the grass.

Among the most common are roundworm eggs, which survive for years in your yard. Once ingested, the eggs hatch and mature into spaghetti-like roundworms that can cause vomiting and diarrhea in cats.

When Milo then excretes roundworm eggs, they may inadvertently be ingested by humans, especially toddlers, who often put things in their mouths without washing their hands. In humans, animal roundworms can cause blindness, seizures and organ damage.

So, I suggest you treat Milo to an indoor grass mat. "Cat grass," the tender young shoots of wheat, barley, oats, rye and wheat berry, is available at pet supply stores. Or buy the seeds and grow the grass yourself. That way, Milo can enjoy grass whenever he likes, without waiting for you to take him outside on cool summer evenings.

Lee Pickett, V.M.D. practices companion animal medicine in North Carolina. Contact her at vet@askthevet.pet.