Spay surgery can be behaviorally and medically beneficial for your dog. In addition, if you spay your pet, you'll avoid unwanted puppies and help control pet overpopulation. Millions of healthy dogs and cats are humanely put to death each year in the United States simply because there aren’t enough homes to go around. While the traditional age for spaying is six to nine months, puppies as young as eight weeks old can be spayed as long as they’re healthy. Dogs can be spayed as adults as well, although there’s a slightly higher risk of post-operative complications in older dogs who are overweight.
There are significant medical benefits to be gained from spaying your dog. Spaying prevents the following conditions:
- Mammary (breast) cancer Females spayed prior to their first estrus cycle have a significantly reduced risk of developing mammary cancer, a common cancer in unspayed females. The chances of developing this cancer increase if a female isn’t spayed until after her second heat cycle, but they still remain lower than the risk for unspayed females. So if your dog has already gone through her first heat cycle, it’s not too late. Spaying her will still reduce her risk of developing cancerous mammary tumors.
- Pyometra Bacteria can infect a female dog’s uterus, causing a potentially fatal infection. This kind of infection, called pyometra, usually occurs in older females (about seven to eight years of age). Approximately 25% of all unspayed females will suffer from pyometra before the age of 10. If your unspayed female shows signs of lethargy, depression, anorexia, excessive water drinking, vaginal discharge, excessive urination, pale mucous membranes (the skin inside her mouth and nose), vomiting, diarrhea, weight loss, abdominal distension or inflamed eyes, get her to a veterinarian immediately. Having your dog spayed greatly reduces the possibility that she’ll contract pyometra.
- Ovarian and uterine tumors Ovarian and uterine tumors are uncommon in dogs, although some breeds may be predisposed to developing ovarian tumors. Older female dogs are at increased risk. Having your dog spayed completely eliminates the possibility of her developing ovarian or uterine cancer.
- Injury, stress and disease related to having puppies Carrying and giving birth to puppies can be both physically dangerous and stressful for a dog. Spaying eliminates these potential risks.
Dogs become sexually mature when they’re between six and 12 months of age. At this time, female dogs produce a surge of the hormone estrogen and begin the reproductive cycle, which leads to cycles of estrus or “heat.” When in heat, a female dog will be receptive to breeding with males. Most dogs experience two heat cycles per year.
Having your dog spayed won’t affect her working abilities, friendliness, playfulness or personality. However, spaying can affect many behaviors associated with the heat cycle. You may see a reduction in these behaviors after you spay your dog:
- Roaming While in heat, female dogs often try to leave home in search of males, which puts them at risk of getting lost and being injured or killed on roadways. Spaying your dog will reduce or eliminate her drive to roam while in heat. (If you don’t get her spayed, you’ll need to confine your dog indoors or in an escape-proof yard when she’s in heat to prevent escapes and unwanted pregnancies.)
- Frequent urination Females in heat urinate often to attract male dogs with the scent of their urine. Not only will this cause a line-up of neighborhood male dogs at your door, but it can also lead to urine on your carpet and furniture. Spaying your dog will eliminate frequent urination and bloody discharge, both of which may occur during her heat cycle.
- Irritability Each estrus cycle causes significant hormonal changes in a female dog. Some dogs become irritable or nervous and even feel pain due to ovulation. Because spayed dogs don’t experience these hormonal changes, a female dog’s behavior may be more consistent after she’s spayed.
- Aggression Females may be less aggressive toward both dogs and people after they’re spayed. Unspayed females sometimes compete for the attention of a male dog by fighting. Spaying can reduce or eliminate this fighting. Spaying your dog can also eliminate the possibility of hormonally driven guarding behavior. Female dogs will sometimes behave aggressively if people or other pets attempt to approach or touch their puppies. Some dogs who don’t get pregnant during a heat cycle will experience a “false pregnancy” or “pseudopregnancy.” Females in false pregnancy often “adopt” objects and treat them like a litter. These females may guard the adopted objects as if they were real puppies.
To prevent the development of the behaviors listed above, it’s best to spay your dog before she reaches sexual maturity at six to 12 months of age. That way, she’s unlikely to develop unwanted habits associated with her heat. If your dog has practiced these habits for months or years, they might persist even after spaying. However, if you have an older dog, it’s still worth it to spay her. Even if you can’t completely get rid of her problematic behaviors, you might see them less often after she’s spayed—and spaying will still be beneficial to her physical health.
If your dog still has habits you dislike after spaying, like roaming, frequent urination, irritability or aggression, it’s best to seek professional advice. Getting help is particularly important if your dog has an aggression problem. Please see our article, Finding Professional Help , for information about locating a Certified Applied Animal Behaviorist (CAAB), a veterinary behaviorist (Dip ACVB) or a qualified Certified Professional Dog Trainer (CPDT). If you elect to hire a CPDT because you can’t find a behaviorist in your area, be sure to determine whether he or she has professional training and extensive experience in successfully treating aggression, as this training and experience are beyond what CPDT certification requires.
Don’t Spay Your Dog Until After Her First Heat
There’s no behavioral or medical benefit to waiting to spay your dog until after her first heat cycle. In fact, each heat cycle your dog experiences increases her risk of developing serious medical conditions. To best prevent the development of unwanted behavior and medical problems, make plans to spay your dog before she reaches sexual maturity at six to 12 months of age.
Letting a Dog Have One Litter Will Calm Her Down
There’s nothing magical about giving birth that leads to a calmer, better-behaved dog. Two things that do lead to a better-behaved dog are proper obedience training and regular exercise. If you use gentle, consistent training techniques to teach your dog some basic manners, she’ll learn how to control her impulses. (To find a professional in your area who offers classes or private training lessons, please see our article, Finding Professional Help .) Making sure your dog gets at least 30 minutes of aerobic exercise per day, as well as plenty of mental exercise, can also greatly improve her behavior. (Please see our articles, Enriching Your Dog’s Life  and Exercise for Dogs , to learn how to give your dog a great physical and mental workout.) If you have a puppy, keep in mind that maturity may bring calmer behavior, too.
Spaying Is a Quick Fix for All Behavior Problems
Some people think that spaying a dog will get rid of all her behavior problems. Although it often reduces undesirable behaviors caused by the heat cycle, there’s no guarantee that your dog’s behavior will change after she’s spayed. The effects of spaying are largely dependent on your dog’s individual personality, physiology and history. Even if spaying does remedy behavior problems that are influenced by hormones, it’s not a quick fix that will instantly transform your dog into an angelic companion. If you want her to learn polite manners, you’ll still need to teach her basic obedience skills. If you need help with training, please contact a Certified Professional Dog Trainer (CPDT) in your area. If your dog has a more serious behavior problem, such as fear or aggression, and it persists after she’s spayed, please see Finding Professional Help  to learn how to find a qualified professional who can assist you.
Potential Detriments of Spaying
Although spaying is beneficial in many ways, there are a few potential effects to be aware of:
- A small number of studies report that unspayed female dogs who are aggressive to family members may become more aggressive after they’re spayed. This could be caused by a decrease in estrogen and oxytocin, both of which may have calming, anti-anxiety effects.
- Spayed females have an increased risk of developing urinary tract infections.
- Between 5 to 20% of spayed females suffer estrogen-responsive urinary incontinence (or “spay incontinence”), which means they have poor sphincter control and are less able to hold their urine. At least one study found a slightly higher risk in dogs who were less than three months of age when spayed. The risk is higher for overweight dogs, and dogs of certain breeds are predisposed to this condition. Fortunately, this kind of urinary incontinence is almost always easily controlled with medical treatment.
- Dogs who are spayed before they reach their adult size may grow slightly taller than they would have had they not been spayed.
- There is a very slight increased risk for spayed dogs to develop transitional cell carcinoma of the bladder, osteosarcoma and hemangiosarcoma (three kinds of cancer), particularly those breeds that are already predisposed to these diseases.
- Dogs spayed prior to five months of age may be slightly more likely to develop hip dysplasia and cranial cruciate ligament (CCL) rupture, particularly those breeds that are already predisposed to these diseases.
- Spayed dogs are at increased risk of developing hypothyroidism.
- Physiological changes after spaying may affect your dog’s metabolism and appetite, making her prone to weight gain. There’s some evidence to suggest that puppies spayed before five months of age are at greater risk of becoming obese than puppies spayed later. This potential drawback is easily controlled with appropriate diet and exercise. If you notice that your dog looks overweight, you can decrease the amount of food you give her and increase her exercise. If you’re not sure if your dog is at a healthy weight, please consult her veterinarian.
It’s important to realize that the potential drawbacks of spaying are minimal relative to the benefits. However, you should discuss both the benefits and detriments with your veterinarian to make the best decision for the health and well-being of your individual dog.