Spaying and neutering are surgical procedures that remove a pet’s reproductive organs so they can no longer breed. Spaying refers to the surgery performed on female animals, while neutering refers to the surgery performed on males. Together, these procedures are the most common surgeries in veterinary medicine, affecting everything from your pet’s cancer risk to their lifespan.
What Happens During Each Surgery
Spaying is technically called an ovariohysterectomy. The veterinarian makes an incision in the abdomen and removes both ovaries and the uterus. In some cases, the cervix is also removed. Without these organs, the female can no longer go into heat or become pregnant.
Neutering, also called castration, is a simpler procedure. The veterinarian makes a small incision near the scrotum and removes both testicles. Because the surgery doesn’t involve the abdominal cavity, it’s generally shorter and has a faster recovery. The terms apply to both dogs and cats, and the basic approach is the same for both species.
You’ll sometimes hear “neutering” used as a catch-all term for sterilizing any pet, male or female. But in common usage, spaying means females and neutering means males. The informal term “getting fixed” covers both.
Health Benefits of Sterilization
For females, the most significant benefit is a dramatic reduction in mammary (breast) tumor risk. Dogs spayed before their first heat cycle have only 0.5% of the risk of developing mammary tumors compared to intact dogs. After one heat cycle, that protective effect is still strong but drops to about 8% of the intact risk. One study found zero mammary tumor diagnoses in dogs spayed before 6 months of age. Spaying also eliminates the risk of pyometra, a serious and sometimes fatal uterine infection that is relatively common in unspayed older dogs and cats.
For males, neutering eliminates the risk of testicular cancer entirely, since the testicles are removed. It also reduces the risk of prostate problems later in life.
A University of Georgia study that examined over 40,000 dog death records found sterilized dogs lived an average of 9.4 years compared to 7.9 years for intact dogs. That’s roughly a year and a half of additional life expectancy.
Behavioral Changes to Expect
Neutering tends to reduce certain hormone-driven behaviors in male dogs, but it’s not a personality overhaul. Research shows neutered males display less mounting behavior, less leash-pulling, and less roaming. There’s also a tendency toward reduced owner-directed aggression. However, the same research found no significant change in marking behavior, inter-male aggression toward strangers, or habits like chewing, play, and exploration. If a behavior is driven by habit or anxiety rather than hormones, neutering won’t fix it.
Spayed females stop going into heat, which means no more bloody discharge, restlessness, or attracting male dogs from the neighborhood. For cats, spaying eliminates the loud vocalizing and constant pacing that come with heat cycles.
Weight and Metabolism After Surgery
One real downside of sterilization is its effect on metabolism. Research on cats found that spayed females experienced a significant drop in resting metabolic rate, from about 84 to 67 calories per kilogram of body weight per day. At the same time, daily food intake went up. This combination makes weight gain almost inevitable if you keep feeding the same amount.
The practical takeaway: you’ll likely need to reduce your pet’s food portions by 20 to 30 percent after surgery and monitor their weight closely for the first few months. Your vet can help you adjust portions based on your pet’s size and activity level.
Risks for Large Breed Dogs
Sterilization isn’t without tradeoffs, particularly for bigger dogs. Research from UC Davis found that mixed-breed dogs weighing more than 44 pounds as adults face a higher risk of joint disorders if spayed or neutered before 1 year of age. These include hip dysplasia, elbow dysplasia, and cranial cruciate ligament tears (a common knee injury). For female dogs over 43 pounds, the risk of joint disorders jumped from 4% in intact dogs to 10 to 12% in those spayed before age one.
Dogs under 43 pounds showed no increased joint risk regardless of when they were sterilized. The researchers also found no increased cancer risk in any weight category for mixed-breed dogs, which was reassuring given earlier concerns about certain cancers in sterilized pets.
When to Schedule the Surgery
For cats, the recommendation is straightforward. The AVMA, the American Association of Feline Practitioners, and several other veterinary organizations all support spaying or neutering cats by 5 months of age.
For dogs, timing is more individual. There’s no single recommended age that works for every breed and size. Small dogs can typically be sterilized earlier without added risk, while large and giant breeds may benefit from waiting until they’re closer to full skeletal maturity, usually around 12 to 18 months. Your vet will factor in breed, sex, expected adult size, and your dog’s living situation. One thing the evidence is clear on: there is no known benefit to letting a female dog or cat go through her first heat cycle before spaying, despite the persistent myth that it’s somehow healthier.
Recovery After Surgery
Most pets bounce back quickly, but the first two weeks require some management. Your pet may be groggy and nauseous from anesthesia for the first day or two, and it can take up to 48 hours for their appetite to return to normal. Encourage gentle movement indoors during this period rather than letting them sleep it off completely, as staying active helps clear the anesthesia faster.
For the full 10 to 14 days after surgery, your pet needs exercise restrictions: no running, jumping, swimming, or rough play. The incision site needs to stay dry and undisturbed. Most vets will send your pet home with an Elizabethan collar (the plastic cone) to prevent licking and chewing at the stitches, and it should stay on for the entire recovery window. Neuters in males tend to heal faster since the incision is smaller and external, while spays involve abdominal surgery and may take the full two weeks.
The Bigger Picture: Shelter Populations
Beyond individual health, spaying and neutering play a direct role in controlling pet overpopulation. In 2024, 5.8 million dogs and cats entered shelters and rescues in the United States. Sixty percent of those animals arrived as strays, and 29% were surrendered by owners who could no longer care for them. A single unspayed cat can produce dozens of kittens over her lifetime, each of which can reproduce within months. Community spay and neuter programs remain one of the most effective tools for reducing these numbers over time.