When a female dog is spayed, a surgeon removes her ovaries (and sometimes the uterus) under general anesthesia, permanently ending her ability to reproduce and her heat cycles. The surgery typically takes 20 to 90 minutes depending on the dog’s size, and the overall risk of a serious complication is very low. But the effects go well beyond the operating table. Spaying changes your dog’s hormones, metabolism, behavior, and long-term disease risk in ways worth understanding before and after the procedure.
What the Surgeon Actually Removes
There are two versions of the surgery. The traditional approach, called an ovariohysterectomy, removes both the ovaries and the uterus through an incision in the abdomen. The less invasive option, an ovariectomy, removes only the ovaries and leaves the uterus in place. Many surgical textbooks still recommend removing the uterus out of concern that it could develop disease later, but a long-term study following dogs for 8 to 11 years after surgery found no significant difference in urogenital problems between the two methods. The researchers concluded that removing the uterus during routine spaying in healthy dogs is unnecessary, and that ovariectomy should be considered the preferred approach. In practice, many veterinarians in the U.S. still perform the traditional method, while ovariectomy is more common in Europe.
How Hormones Change Immediately
Because the ovaries produce nearly all of a female dog’s reproductive hormones, removing them causes a rapid and permanent drop. Within one week of surgery, progesterone, testosterone, and cortisol levels all fall significantly and stay low. Progesterone, which normally rises and falls with each heat cycle, drops to roughly a quarter of its pre-surgery level. Testosterone, which female dogs produce in small amounts, plummets as well. These aren’t temporary dips. Without ovaries, the hormonal signals that drive heat cycles, attract males, and support pregnancy simply stop.
Reduced Cancer and Infection Risk
The timing of spaying has a dramatic effect on mammary tumor risk, which is the most commonly cited health benefit. Dogs spayed before their first heat cycle retain only 0.5% of the mammary tumor risk compared to intact dogs. After one heat cycle, that risk climbs to 8%. Dogs spayed after three or more cycles have significantly higher rates: 27.6% compared to 9.4% for those spayed before the third cycle. Since roughly half of mammary tumors in dogs are malignant, early spaying offers meaningful cancer protection.
Spaying also eliminates the risk of pyometra, a bacterial infection of the uterus that affects up to 25% of intact female dogs over their lifetime. Pyometra can be life-threatening and often requires emergency surgery to remove the infected uterus. By removing the reproductive organs electively, the condition simply cannot develop.
Weight Gain and Metabolism
One of the most predictable side effects of spaying is a slower metabolism. Resting metabolic rate drops after surgery, meaning your dog burns fewer calories at rest doing the same activities as before. Research measuring the energy needs of dogs before and after spaying found that caloric requirements fell by roughly 5% in the first 12 weeks. That may sound small, but it adds up. In cats, a 30% calorie reduction was needed to prevent weight gain after the same surgery, and dogs follow a similar pattern if food intake isn’t adjusted.
A study testing different diets after spaying found that high-protein, high-fiber diets helped limit weight gain and body fat increases, and also kept cholesterol and triglyceride levels in better shape. The benefits were most obvious when dogs were allowed to eat freely, which is how many owners feed their pets. If your dog is spayed, switching to a controlled feeding schedule with measured portions is one of the most effective things you can do to prevent gradual weight creep over the following months.
Behavioral Changes to Expect
Spaying tends to reduce behaviors driven by reproductive hormones. Restlessness during heat cycles stops entirely. Roaming (the urge to escape and find a mate), urine marking, mounting, and competition-driven aggression all typically decrease. Many owners notice their dog is generally calmer, particularly if she was anxious or high-energy before surgery.
What doesn’t change is your dog’s core personality. Playfulness, affection, intelligence, trainability, and how she bonds with people all remain the same. Behaviors shaped by past experience rather than hormones, like habits she learned before surgery, may also persist. A dog who learned to mark territory indoors, for example, may continue doing so out of habit even after the hormonal drive fades.
There is one nuance worth knowing. Some research suggests that females spayed before one year of age may show slightly increased aggression toward other dogs, or mild increases in anxiety. This doesn’t happen in every dog, and the effect is subtle compared to the behavioral improvements most owners see. But it’s a factor some veterinarians consider when recommending the best age for the procedure.
Urinary Incontinence Risk
Spayed female dogs have a higher risk of developing urinary incontinence later in life, caused by weakening of the muscles that control the bladder. One study found that nearly one in five spayed dogs was affected, regardless of whether the surgery was performed through a traditional incision or laparoscopically. The risk increases with age and the number of years since the surgery. Larger breeds tend to be more susceptible. The condition is manageable with medication in most cases, but it’s one of the few long-term downsides of spaying that owners should be aware of.
How Safe Is the Surgery?
Spaying is one of the most commonly performed veterinary surgeries, and the risk of death is extremely low. A review of over 42,000 dogs undergoing spay or neuter surgery at a single high-volume clinic found a mortality rate of 0.009% for dogs overall. Female dogs had a slightly higher risk than males (0.05% vs. 0.02%), which reflects the fact that spaying is a more invasive abdominal procedure than neutering. To put that in perspective, fewer than 1 in 2,000 female dogs experienced a fatal complication.
The First Two Weeks of Recovery
Most dogs go home the same day as surgery. You can offer water and a small meal that evening, but don’t be alarmed if your dog vomits or has a reduced appetite for the first 24 to 48 hours. If she keeps a small meal down for at least an hour, you can offer another one later. Frequent small meals are especially important for puppies, who need to eat regularly.
The critical recovery window is 10 to 14 days. During this time, your dog should be kept quiet: no running, jumping, or climbing stairs. Walks on a leash for bathroom breaks are fine, but otherwise she should stay in a crate or confined indoor space. This isn’t optional. The highest risk period for sutures breaking down is days 3 through 5 after surgery, and excessive movement can cause the incision to open.
Your dog will need to wear a cone (e-collar) for the full 10 to 14 days to prevent licking at the incision. No baths during this period either, since soap and water can irritate the surgical site or introduce bacteria. Most female dogs receive absorbable sutures that dissolve on their own over one to two months, so a return visit for stitch removal is usually unnecessary.
What the Incision Should Look Like
Check the incision at least twice a day. A normal healing incision has edges that touch each other neatly, with skin that’s a normal pink or slightly reddish color. Mild redness in the first few days is expected. Some bruising may appear a day or two after surgery and can spread wider than the incision itself, which looks alarming but is just blood seeping under the skin surface. A small amount of blood seepage in the first 24 hours is also normal, especially if your dog has been moving around.
Signs that something is wrong include continuous dripping of blood or fluid, intermittent bleeding that lasts beyond 24 hours, swelling or excessive redness, foul smell, discharge, or any sign that sutures have come loose. If the wound edges are gaping apart rather than touching, that needs veterinary attention promptly.