Training indoor cats to become outdoor cats should be a gradual process to ensure a favorable transition that appropriately acclimates your kitty to an entirely new living environment. Keep in mind that outdoor cats are more prone to accident and injury than indoor cats, so taking preventive steps to protect your kitties is vital to their safety and longevity.
Take it Slow
Cats who are used to being indoors need a slow transition to outside living. Start with 10-minute intervals and monitor your cats. Use treats to call them back inside. Work up to a routine and let cats in and out at the same time of day so they become accustomed to the regularity of their schedules. Continue to spend quality time with them, either indoors or outside, to let them know they're loved and cared for.
Make sure your cats are fully vaccinated and in good overall health before you let them outside and continue to take them for regular veterinary exams. This will help protect them in the event they get into fights or injure themselves in any way. Think twice about making declawed inside cats outside cats, as they will lack the basic mechanisms most cats need to defend themselves and hunt.
Provide Food and Water
Your indoor cats are likely used to having regular access to food, water and shelter, so replicate those conditions as best as possible outside, particularly in the early transition stages. Your cats should have a supply of fresh water, and you may need to check daily food allocation to ensure other neighborhood pets or wild animals are not eating their food. Consider establishing a daily feeding routine so your cats instinctively know when to come home and eat.
Provide Shelter and Safety
Create a safe spot for your cats so they can seek protection if necessary. This may be a kitty door that leads into your home, a garage or a shed, or it may be an enclosed structure with warm, dry bedding like straw. Always provide warm shelter for your cat in inclement weather and bring them in at night if possible. You may want to place a litter box outside, both as a sense of familiarity for your cats and as a way to keep your pets from defecating on neighbor's property. Let your neighbors know you have outdoor cats so they don't call a shelter or animal control to remove them.
Spay or Neuter
Spay or neuter cats before allowing them to roam outside. Not only will this reduce the potential for creating unwanted litters of kittens, it also will help to prevent howling and traveling far distances from the home in search of a mate. When female cats are in heat or male cats are seeking a female in estrus, they are more prone to ignoring outside dangers and are more likely to be hit by cars or otherwise injured.