“Altered” is the veterinary term for a dog that has been surgically sterilized, meaning spayed (for females) or neutered (for males). If someone at a shelter, vet clinic, or breeder tells you a dog is “altered,” they’re simply saying the dog can no longer reproduce. The opposite term is “intact,” which means the dog still has its reproductive organs.
What the Surgery Actually Involves
For female dogs, spaying typically means removing the ovaries, fallopian tubes, and uterus. Some veterinarians remove only the ovaries, which achieves the same sterilization but is a slightly less involved surgery. Either way, the dog loses its ability to reproduce and stops producing the hormones that drive heat cycles.
For male dogs, neutering means removing the testicles. This eliminates the main source of reproductive hormones like testosterone, which is why neutering can reduce or eliminate breeding-driven behaviors like mounting, roaming, and urine marking.
How Altering Affects Behavior
One of the most common reasons people alter their dogs, beyond preventing unwanted litters, is to address behavioral issues tied to hormones. Research on castrated dogs found that behavioral problems were reduced or disappeared entirely in 74% of males and 59% of females after the procedure. Hypersexuality and related behaviors showed the most consistent improvement.
Aggression can also improve. In one study, 49 out of 80 aggressive male dogs and 25 out of 47 aggressive female dogs became more gentle after being altered. That said, it’s not a guaranteed fix. A small number of female dogs in the same study actually became aggressive only after being spayed, which suggests hormones aren’t the sole driver of behavioral issues. If your dog has aggression problems, altering alone may not resolve them.
When Dogs Are Typically Altered
The ideal timing depends on your dog’s expected adult size. The American Animal Hospital Association recommends small-breed dogs (under 45 pounds as adults) be neutered at six months of age, with females spayed before their first heat cycle, which typically arrives around five to six months. Large-breed dogs (over 45 pounds as adults) should wait longer, ideally until growth stops, which is usually between 9 and 15 months of age.
The reason for the size-based difference comes down to joint health. Research from UC Davis found that mixed-breed dogs weighing more than 44 pounds as adults face a higher risk of joint disorders like hip dysplasia, elbow dysplasia, and knee ligament tears if they’re altered before one year of age. For female dogs over 43 pounds, the risk of joint problems jumped from 4% in intact dogs to 10-12% in those spayed before age one. Dogs under 43 pounds showed no increased joint risk regardless of when they were altered. The study found no increased cancer risk in any weight category compared to intact dogs.
For large-breed females, your vet can help narrow the recommended window to somewhere between 5 and 15 months based on your specific dog’s breed, health risks, and lifestyle.
Weight Gain After Altering
One thing many owners don’t expect is how significantly altering changes a dog’s metabolism. Sterilized dogs tend to eat more while simultaneously burning fewer calories at rest. The Purina Institute recommends reducing a dog’s caloric intake by about 30% after the procedure to account for lower energy needs. If you keep feeding the same amount as before, weight gain is almost inevitable. Switching to a food formulated for neutered dogs or simply measuring portions more carefully can prevent this.
Recovery After Surgery
Recovery from spaying or neutering takes about 10 to 14 days. During that window, your dog needs to stay quiet: no running, jumping, swimming, or rough play. Strenuous activity can cause swelling around the incision, which may lead to sutures dissolving too early or the incision reopening.
You’ll also need to keep your dog from licking, scratching, or chewing at the incision site, which is where the classic cone (or a recovery suit) comes in. The incision should stay dry, so skip baths and keep your dog out of water until your vet gives the all-clear. Male dogs generally bounce back a bit faster since neutering is a less invasive procedure than spaying, but the same activity restrictions apply to both.
What It Costs
The national average cost for spaying a female dog is around $455, with prices ranging from roughly $360 to $830 depending on your location, the dog’s size, and the clinic. Neutering a male dog averages about $487, ranging from $385 to $885. Spaying tends to be slightly cheaper because the surgery, while more invasive, is more standardized across clinics.
If cost is a barrier, local animal shelters and rescue organizations frequently offer free or heavily discounted spay and neuter events. Many cities also have dedicated low-cost clinics that perform these surgeries at a fraction of private practice prices. Your local shelter is the best starting point to find these options.