Dogs have their testicles removed primarily to prevent reproduction, reduce hormone-driven behaviors, and eliminate the risk of several common diseases. The surgery, called castration or neutering, is the most widely performed elective procedure in veterinary medicine and has effects that go well beyond preventing puppies.
What the Testicles Actually Do
A dog’s testicles are the main source of testosterone and a significant source of estradiol, the two hormones that drive male reproductive behavior and development. Testosterone is responsible for fertility, but it also fuels behaviors like roaming, urine marking, mounting, and competition with other male dogs. Inside the prostate gland, testosterone gets converted into a more potent hormone that causes the prostate to grow steadily throughout a dog’s life.
When the testicles are removed, production of these hormones drops almost immediately. The brain’s hormonal feedback loop, which normally keeps testosterone levels in check, loses its signal. The result is a rapid and permanent shift in the dog’s hormonal environment.
Preventing Overpopulation
The most straightforward reason for neutering is to stop dogs from breeding. A single intact male can sire dozens of litters in its lifetime, and shelters across the country take in millions of dogs each year. Puppies born in shelters or surrendered as part of unplanned litters add to a population that already exceeds the number of available homes. Neutering is the most reliable way to take an individual dog out of the breeding equation permanently.
Reducing Problem Behaviors
Testosterone drives several behaviors that make intact male dogs harder to live with. Roaming, where a dog escapes or wanders in search of a female in heat, is reduced in about 90% of dogs after castration. Urine marking indoors, mounting people or other animals, and aggression toward other males are also tied to testosterone and typically decrease after the surgery. These aren’t guaranteed fixes, especially for behaviors that have become deeply ingrained habits, but the hormonal motivation behind them disappears.
Eliminating Testicular Cancer Risk
Testicular tumors are one of the most common cancers in intact male dogs, accounting for roughly 20% of all tumors in males. Population-based data from a canine cancer registry in central Italy found a median incidence of 35 cases per 100,000 dogs. Removing the testicles eliminates this risk entirely, since the tissue where these tumors develop no longer exists.
Protecting the Prostate
Benign prostatic hyperplasia, a noncancerous enlargement of the prostate, is the most common prostate condition in intact male dogs. It develops because testosterone continuously stimulates prostate tissue to grow, and it becomes increasingly likely as a dog ages. An enlarged prostate can cause difficulty urinating, bloody discharge, constipation, and discomfort.
Castration is the standard treatment. Once testosterone production stops, the prostate begins to shrink within weeks and typically returns to normal size within a few months. For dogs not intended for breeding, neutering prevents the condition from developing in the first place.
How the Surgery Works
The procedure is performed under general anesthesia and typically takes 15 to 30 minutes. There are two common surgical approaches. In the pre-scrotal method, the veterinarian pushes each testicle forward through a single incision made just in front of the scrotum. In the scrotal method, the incision is made directly on the scrotum. In both cases, the blood vessels and the tube that carries sperm are tied off with absorbable sutures before each testicle is removed.
The scrotum itself is usually left in place. It will gradually shrink and flatten over the following weeks as the tissue contracts. The incision is closed with sutures or surgical glue, and most dogs go home the same day.
What Recovery Looks Like
The recovery period lasts 7 to 10 days. During this time, your dog should avoid running, jumping, playing with other animals, and long walks, as any of these can reopen the incision or cause swelling. Keep the incision dry for the full 10 days, which means no baths and no topical ointments. A cone or recovery suit prevents licking and chewing at the surgical site, which is the most common cause of complications. Most dogs are back to normal activity within two weeks.
The Weight Gain Trade-Off
Neutering does come with metabolic consequences. Removing the testicles lowers a dog’s resting metabolic rate, meaning the body burns fewer calories at rest than it did before surgery. Research on spayed female dogs found that their daily calorie needs dropped by roughly 5 to 10% after surgery, and similar reductions occur in neutered males. Without adjusting food portions or increasing exercise, weight gain is common. Some studies in cats have found that a 25 to 30% calorie reduction was necessary to prevent post-surgery weight gain.
This doesn’t mean neutering guarantees an overweight dog. It means you’ll likely need to feed less food or switch to a lower-calorie diet after the procedure. Your dog’s appetite may actually increase while its calorie needs decrease, so monitoring body condition becomes important.
Timing Matters, Especially for Large Breeds
When to neuter is just as important as whether to neuter, and the answer depends heavily on your dog’s breed and size. In large and giant breeds, neutering before the growth plates close can lead to bones growing slightly longer than normal, which may shift joint alignment enough to increase the risk of ligament tears and other joint disorders. A large study covering 35 breeds found that dogs neutered before one year of age had 2 to 4 times the rate of joint problems compared to intact dogs, with the highest risk in those neutered by 6 months.
For Golden Retrievers, the suggested guideline is to delay neutering until beyond one year of age. For German Shepherds and Bernese Mountain Dogs, the recommendation extends to beyond two years. Great Danes, despite their enormous size, didn’t show a clear spike in joint disorders after neutering, but waiting well past the first year is still considered prudent given their slow skeletal development. Small breeds, by contrast, showed no meaningful increase in joint problems at any neutering age.
Vasectomy as an Alternative
A vasectomy, which cuts the sperm-carrying tubes while leaving the testicles in place, is a less common option that preserves hormone production while still preventing reproduction. Dogs that retain their testicles keep the protective effects of testosterone on joints and metabolism. A comparative study found that longer exposure to gonadal hormones, regardless of whether the dog could still reproduce, was associated with fewer general health problems and fewer problematic behaviors. The trade-off is that a vasectomized dog still has testosterone-driven behaviors like roaming and marking, and still faces the risk of testicular tumors and prostate enlargement. Vasectomy is worth discussing with your veterinarian if hormone preservation is a priority, but it’s not a one-size-fits-all solution.