Study compares the health of indoor versus outdoor cats

Analysis by Dr. Karen Shaw Becker

outdoor cats

Story at-a-glance -

  • The results of a recent study present a “surprise” conclusion: outdoor cats are three times as likely to contract infectious parasites than indoor cats
  • Beyond parasites and infectious diseases, cats who roam free outdoors face many other threats, including moving vehicles, predators and cruel humans
  • To keep your feline family member healthy, keep him indoors, but allow him supervised time outside with harness walks or a secure catio (cat patio)
  • Also take steps to optimize your indoor cat’s lifestyle

For years now I've assumed it's common knowledge that cats who live indoors are generally healthier with longer lifespans than free-roaming kitties who spend most or all of their time outdoors. However, the "surprise" results of a recent study have me second-guessing myself!

A group of Auburn University researchers evaluated nearly two dozen studies from around the globe and arrived at the conclusion that outdoor cats are much more likely (three times as likely) to come into contact with infectious parasites than indoor cats. The research team was surprised by these results, which is, well, surprising!

"I was expecting that maybe infections that were spread from cat to cat wouldn't be as influenced by outdoor access," lead study author Kayleigh Chalkowski to The New York Times, "but they were all influenced the same."1

Hmm. While it's true certain infections can be spread from cat to cat indoors, the parasites that host such infections are generally found outdoors. It seems obvious, at least to me, that cats who live entirely indoors either as only pets or with other indoor-only kitties have very little chance of being exposed to outdoor parasites.

Across the globe, indoor cats have minimal risk of parasitic infection

The research team analyzed at a total of 21 studies from the U.S., Europe, Australia, Pakistan, Chile, Brazil and other locations that looked at parasitic infections in indoor-only cats compared to outdoor and indoor-outdoor cats, excluding feral cats. Their findings were published in the journal Biology Letters.2

"Over so many different studies, with so many different parasites, in so many different countries: No matter where you keep your cat indoors, it reduces risk of parasitic infection," Chalkowski told the NYT.

Again, I'm surprised at the tone of surprise; it seems obvious to me that indoor animals would have substantially less exposure to parasites and therefore fewer infections. This is one reason I'm completely opposed to the "routine deworming" of indoor animals; it's unlikely they would acquire parasites because most modes of transmission happen outside the home.

Perhaps the Auburn researchers have been influenced by the manufacturers and retailers of chemical pet pest prevention products who would like us all to believe the average housecat is crawling with fleas, ticks, mites, intestinal parasites and other assorted bugs. The commonsense truth is that if your feline family member never goes outdoors, there's not much chance she'll run into any bugs at all.

Other dangers indoor-only cats avoid

Parasitic infections are but one of many threats faced by indoor-outdoor and outdoor-only kitties. The biggest is actually trauma, usually involving getting hit by a car. Thanks to KittyCams, researchers have been able to learn plenty about the kinds of risky business free-roaming cats get up to when they're wandering around outdoors, including:3

Crossing roads

Climbing trees

Having non-aggressive contact with unfamiliar cats (infectious disease risk)

Climbing on roofs

Consuming solids or liquids not left by owners

Having contact with wild animals (injury and disease risk)

Entering storm drains

Crawling into car engines

Cats are also prey for wildlife such as coyotes, mountain lions, wolves and raptors, and fights among outdoor cats can also lead to serious injury and infections, including bite abscesses. Sadly, cruel humans also pose a grave risk to cats through gunshots, poisonings, burnings and asphyxia.4

As discussed earlier, infectious diseases, several of which are zoonotic (can be spread to humans) commonly sicken and kill outdoor cats, including feline retroviruses, mycoplasmosis, toxoplasmosis, bartonellosis (cat scratch fever), tularemia, plague and rabies, along with worms, ectoparasites and fungal infections.

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Bottom line — Keep your cat indoors

The takeaway message here is that if you want your cat to remain healthy, with a nice long lifespan, she should live exclusively indoors. While being indoors all the time isn't what most cats would choose, it's by far the safest life we can choose for them.

Indoor living isn't an entirely natural environment for your cat but letting her run around loose outside presents much more risk than keeping her "captive" in your home. However, just because your kitty lives inside doesn't mean she can't go on supervised visits outside to bask in the sun, exercise and ground herself on a daily basis, if she chooses. Think of housecats like toddlers; they should live inside but should have some outdoor time daily, weather permitting. Outdoor adventures are wonderful for cats, as long as they're safe.

I recommend walking your cat in nice weather using a harness. This gets him out into the fresh air, stimulates his senses and gets his paws in direct contact with the ground. An alternative is a safe, fully enclosed catio that prevents him from getting out and other animals from getting in.

Tips to help your 'captive' cat thrive indoors

Here are a few recommendations that can provide your cat with an optimal life indoors:

Feed a moisture-rich, nutritionally balanced, species-appropriate diet — Feeding your cat an optimal diet is the single most important thing you can do to help her have a long, healthy life. That's why it's important to understand that some foods are metabolically stressful, for example, all dry (kibble) formulas, processed pet food (canned or dry) containing feed-grade (versus human-grade) ingredients and diets containing grains, potatoes or other starchy foods.

The nutrition that generates the least amount of metabolic stress for most cats, regardless of age, is their ancestral diet: whole, raw, unprocessed, organic, non-GMO and in its natural form. Animal meat should be the foundation of your kitty's diet throughout her life. Filtered, pure, fresh water offered out of nontoxic metal or glass (not plastic) bowls is also important.

Keep your cat at a healthy weight — Tragically, the majority of cats in the U.S. are overweight or obese. The obesity-related diseases overweight kitties inevitably acquire shorten their lifespans and often destroy their quality of life along the way. If you want your kitty around and able to get around comfortably for 20 years, one of the worst things you can do is encourage him to get fat.

The first step in keeping your cat at a healthy weight is to feed an optimal diet as I described above. It's equally important not to free-feed. It's also important to calculate kcal (kilocalorie) requirements for your cat's ideal weight and include treats in his total daily calorie count.

Make sure she gets daily exercise — Consistent daily exercise, including at least 20 minutes of high-intensity activity will help your cat burn fat and increase muscle tone. Make sure she has things to climb on, like a multilevel cat tree or tower. Think like a cat and choose toys and activities that answer her need for hunting, stalking and pouncing on her "prey."

Because our cats don't have the freedom they would in the wild, it's up to us to give them opportunities to practice those natural instincts. A great way to do that is to have your kitty "hunt" for her food. Try separating her daily portion of food into three to five small meals fed throughout the day in a variety of puzzle toys or indoor hunting feeder mice.

This will encourage your cat to "hunt" and eat on a schedule similar to his wild cousins, and as an added bonus, he might just sleep through the night thanks to the puzzle toy you give him at bedtime.

Enrich kitty's indoor environment — The term "environmental enrichment" means to improve or enhance the living situation of captive animals to optimize their health, longevity and quality of life. The more comfortable your cat feels in your home, the lower her stress level. Reducing kitty's stress is extremely important in keeping her physically healthy.

Enriching your cat's surroundings means creating minimally stressful living quarters and reducing or eliminating changes in her life that cause anxiety. Jackson Galaxy has written several books on creating feline environmental enrichment around the house that I highly recommend.

The essentials of your kitty's life — food, water and litterbox (which should be kept immaculately clean), should be located in a safe, secure location away from any area that is noisy enough to startle her or make her feel trapped and unable to escape. Cats are natural climbers and scratchers, so kitty needs approved places for climbing and scratching in her indoor environment. She also needs her own resting place and a hiding place (sometimes these are the same spot) where she feels untouchable.

Think about what you can do to appeal to your kitty's visual, auditory and olfactory senses. For example, some cats can gaze out the window for hours, while others are captivated by fish in an aquarium. Some even enjoy kitty videos.

When you're away from home, open all your shades and blinds to provide natural light during the day. Provide background noise for kitty that is similar to the ambient sounds she hears when you're home, for example, nature music or a TV at low volume. You can stimulate your cat's keen sense of smell with cat-safe herbs or synthetic feline pheromones.

Schedule regular veterinary wellness exams — I recommend twice-yearly wellness visits because:

Changes in your kitty's health can happen in a short period of time, especially on the inside where you can't see it, like sudden changes in kidney health

Sick cats often show no signs of illness, but early detection allows for early intervention

Semi-annual visits give you and your veterinarian the opportunity to closely monitor changes in your kitty's behavior and attitude that require further investigation

At a minimum, younger healthy cats should see the vet once a year. Kitties over the age of 7 and those with chronic health conditions should be seen twice a year or more frequently if necessary.

I recommend that you find a veterinarian whose practice philosophy you're comfortable with. This may be a holistic or integrative veterinarian, or a conventional veterinarian who doesn't aggressively promote vaccines, pest preventives or veterinary drugs at every visit. Housecall vets can be a great, lower stress option for indoor kitties.

Generally speaking, if you're dealing with a conventional vet, you'll need to advocate for your cat and push back as necessary, politely but firmly. Always remember that you have the final say in what treatments and chemicals are administered to your pet.