It might surprise you to learn that spaying a female dog before her first heat and neutering a male before he reaches sexual maturity can prevent many health and behavior problems. Contrary to the old wives' tale, female dogs absolutely do not need to have one litter (or one heat) before being spayed. In fact, just the opposite is true. Spay and neuter surgeries are easy to perform on young puppies. It takes less time and requires less anesthesia thanks to new technology and new drugs. Young pups and kittens recover more quickly than older animals, and the long-term health benefits include a much smaller risk of developing mammary tumors and no risk at all of dangerous uterine infections or testicular cancer. Dogs and cats that are spayed or neutered before they hit puberty have a much greater chance of living a long, full life.
A common myth about spaying and neutering is that an altered dog or cat will get fat. The truth is that weight gain and loss in animals runs by the same rules as for humans. Too much food and not enough exercise -- not spaying and neutering -- are what causes animals to gain weight.
Spaying or neutering your pet also has a positive effect on behavior. If there's a female dog or cat in heat practically anywhere in the known universe, an unaltered male will know it. He'll try to get out, roam far and wide, mark your furniture and other things with urine, and may become overly aggressive. An un-spayed female goes through the mess of heat about twice a year, during which she may also try to escape or become more unpredictable in her behavior. Without the ebb and flow of those hormonal tides, spayed and neutered pets are more consistent in their temperament which makes training easier, yet their drive in protecting you and your home will remain the same.
Spaying and neutering have one other important benefit that often gets overlooked: They prevent the birth of unwanted puppies and kittens. According to the Humane Society of the United States, 25 to 35 million animals are put to sleep each year because there just aren't enough homes for them. Even if you let your pet have a litter and find homes for every last puppy or kitten, that simply means there's an equal number of puppies and kittens somewhere else who didn't get those homes and will end up being put to sleep.
Your pet should be altered by the age of four to six months, unless your veterinarian recommends waiting longer. Spaying or neutering is a one-time investment. Many animal shelters even have low-cost spay and neuter programs which dramatically lower your pet’s risk of several serious diseases, including some cancers, and doubling your dog's life expectancy.