Here's how to keep your smart, active friend happy and healthy.

Background
The domestic rat is a descendant of the wild brown rat (Rattus norvegicus) and has been bred as a pet for about a hundred years. Pet rats are less fearful than their wild cousins, and when handled gently they quickly learn to enjoy riding on their human friends' shoulders and napping in their laps.

The average rat ranges from 14 to 18 inches long, including tail. These companion rodents come in a variety of coat types and colors, from curly and shiny to black, white and black-and-white. If well cared for, rats typically live two to three years.

Baby rats can be removed from their litters at about six weeks of age. They are able to reproduce at this time, so it is recommended that males and females be kept separately. Rats are full grown at six months of age. Adult males, called bucks, generally weigh 400 to 700 grams, and adult females (known as does) are significantly smaller at 200 to 500 grams.

Rats can be great pets for kids, but young caretakers should always be supervised by an adult. These animals are not toys and should be treated gently.

Housing
Rats are very social with members of their own kind, and should be kept in pairs at least. A pair of females is recommended for first-time rat caretakers. Males will do well together generally only if introduced when they are young. Females, on the other hand, are more accepting of new friends when introduced later in life. Do not house males and females together, as they will breed-and breed. The average rat litter is 12 young and can be as high as 20. Care needs to be taken to separate males and females when they are six weeks of age to avoid unwanted litters.

Rats do best in wire cages because they enjoy climbing, and there is good ventilation. A cage that is 2' x 2' x 2' will generally do for a pair of rats-if you plan to keep more than that, you'll need a larger cage. The floor should be solid, and a beddingbedding of aspen or pelleted recycled paper should be provided. Do not use pine or cedar shavings, which can be harmful to your pets.

A large, multi-level cage designed for ferrets can also make a great rat home, as can a large aquarium. If you opt for the latter, it will require a screen cover to provide ventilation, and will probably need to be cleaned more often than a wire cage to keep odor problems under control.

Whatever type of cage you choose, don't forget the furniture! Provide small boxes or flower pots to hide in, and PVC tubes for your rats to run through. You can also add a tree branch for them to climb on. Some rats enjoy running on an exercise wheel, so you may want to get yours one. Make sure that the wheel has a solid surface without wire rungs, so their tails cannot get caught while running.

Rats can be prone to colds, so be sure to keep the cage out of drafts. Intense direct sunlight should also be avoided.

Diet
Your pets will do well on rat blocks (sometimes called lab blocks), a high-quality pellet chow formulated for rodents. Look for a brand that lists soymeal as its main ingredient. This food should be available at all times.

You can supplement your rats' diet with some fresh fruits and vegetables every day. Peas, broccoli, carrots, apples and bananas are good foods to start with, but it's fun to try new things and find out your pets' favorites. Rats love people food, and you can give yours the occasional table scrap, such as cooked pasta or a bit of pizza crust. Treats need to be limited to prevent obesity.

Do not give your rats chocolate, corn, candy, caffeinated beverages, cheese and sticky foods such as taffy and peanut butter.

Fresh, clean water should be available at all times. A water bottle with a drinking tube that attaches to the side of the cage is the best way to go.

General Care
Remove droppings, uneaten food and soiled areas of bedding from your pets' cage every day.

Clean the cage completely once a week by replacing dirty bedding and scrubbing down the rest of the cage with warm, soapy water.

Like that of all rodents, a rat's front teeth grow continuously. Provide unpainted, untreated pieces of wood, dog biscuits or safe cardboard or rawhide chew toys for your rats to gnaw on. This is crucial for keeping their teeth in tip-top condition and preventing dental problems.

Rats LOVE to play with toys, and a bored rat is an unhappy rat. You can offer yours many of the same toys that are enjoyed by parrots, including swings and ropes for climbing.

Rats are friendly and curious by nature, but you'll need to get your pets used to you- and used to being handled. Start by feeding them small treats. When they're comfortable with that, you can pick them up, one hand supporting the bottom, the other over the back. When you get to know each other better, don't be surprised if your little guys want to snuggle and be petted.

Once your rats are hand-tamed, you should let them play outside of the cage in a safe, secure area for an hour or so every day. This out-of-cage playtime will keep your smart, active friends mentally stimulated and physically fit-just be sure to supervise at all times, please.

If you think one of your rats is sick, don't delay-seek medical attention immediately.