Whether you have just adopted a purebred puppy or rescued a middle aged mixed-breed dog, the most prevalent topic that arises within the first few veterinary visits is if or when to spay / neuter, and why.  Once you have learned the benefits of spaying and neutering dogs, you can work with your vet to determine the best course of action for your dog.

The decision to spay/neuter is often a very conflicting topic for dog owners as there is a lot of data available to the public.  It can be difficult to know what information to be confident in. Ultimately, the discussion with your family veterinarian is the most priceless tool in any decision-making process regarding your pet, but this article can act as a starting point in forming a foundation of knowledge.

Why Spay / Neuter?

One of the more pressing factors to consider when debating whether to spay/neuter your pet is that the United States has an overpopulation problem with both dogs and cats. According to the Shelter Animals Count- The National Database, over 4 million pets (dogs and cats) were taken to a shelter in 2019. Over 2 million of those animals were dogs, and while there were many happy endings for some of these animals, over 230,000 died in the shelter from either illness or humane euthanasia.

While these numbers have improved over the years and have also drastically been changed by COVID-19 in 2020, they only reflect what participating organizations have been reporting. This means that the statistics presented are likely to be an underestimation of what is truly happening in the shelter scene in the United States.

Population Control: A Main Benefit of Spaying and Neutering

Benefits of Spaying and Neutering Dogs Overpopulation

The overpopulation problem is two-fold. The largest contributing factor is allowing pets to reproduce, either intentionally or unintentionally, while being unable to secure forever homes for all the offspring.

The second contributing factor is the relinquishing of pets by owners who can no longer care for their animals, or who no longer want them. This can mean dropping them off at a shelter, or in many cases, dumping them on a street, leaving them to fend for themselves.

While the intentions of most pet owners are good, accidents may happen such as escaping from a yard or leash. During those periods of unsupervised freedom, it is possible that, if your pet is not spayed or neutered, it could contribute to the overpopulation problem. In fact, it is more likely for an intact dog to escape than a spayed/neutered dog because of the innate drive to roam and reproduce. Therefore, it is best practice to air on the side of caution.

Health Benefits of Spaying and Neutering

Not only does spaying and neutering help with population control, but it can also be a direct health benefit for your pet.


The most common tumor of the female dog is mammary neoplasia with a higher prevalence in certain breeds such as Boxers and Jack Russell terriers. Not surprisingly, the incidence of mammary neoplasia goes up in female dogs over 10 years of age, and more than a quarter of unspayed female dogs will develop mammary tumor in their lifetime.

Unfortunately, mammary tumors in dogs have a 50% chance of being malignant, and 75% of mammary tumors metastasize to other tissues such as the lungs. The good news is that the incidence of mammary neoplasia drastically decreases to 0.5% when female dogs are spayed before their first heat cycle (about 6 months old in most dog breeds).

Reproductive Organ Issues

Female Dogs

Apart from cancer, another condition that intact female dogs can acquire is a pyometra. Pyometra translates to “pus in the uterus” and can occur secondarily to cystic endometrial hyperplasia. Essentially, the hormonal heat cycles of female dogs contribute to changes in the lining of uterus such that it sets up a favorable environment for bacterial growth.

The most common bacteria to be isolated from pyometras is E. Coli. This disease process is very serious, and an emergency, as it can progress to sepsis quickly and often be fatal. Up to 15.2% of intact female dogs get pyometras by 4 years of age, and 23-24% of dogs over 10 years will develop it. While some mild cases can be medically managed, spaying a female dog with a pyometra once she is stabilized is curative. Luckily, pyometras can be completely avoided by receiving a spay (a.k.a. ovariohysterectomy (OHE)) before the disease process ever occurs.

Male Dogs

Male dogs also benefit greatly from being neutered. Like female dogs, males can also get reproductive tract cancers. Testicular tumor prevalence has been reported in the dog population with a range of 0.9%-5.8%, with some studies suggesting even higher prevalence of up to 27%. Luckily, neutering your dog decreases the risk of development of these kinds of cancers to essentially 0%.

Intact male dogs also are at risk of developing benign prostatic hyperplasia as early as 2.5 years old. This disease process occurs with chronic testosterone hormone stimulation and causes nonpainful symmetrical enlargement of the prostate. Cysts are commonly found within the prostate with this disease and can cause bloody urine or discharge and can also create an environment in which a prostatic bacterial infection can occur.

This condition can be treated with castration, and regression of the prostatic growth is evident in a few weeks or months. Beyond treating the disease, it can be prevented entirely by neutering your dog before the development of an altered testosterone:estrogen ratio.

Summary of “The Why” of Spaying and Neutering

While there are many more health benefits to spaying and neutering your dog, it is clear from the brief examples above that performing these quick procedures can drastically lengthen the lifespan of your pet, as well as improve their quality of life.

When to Spay or Neuter

Benefits of Spaying and Neutering Dogs when to spay neuter

Although it seems clear and concise as to why spaying and neutering are beneficial, understanding when to perform these procedures is less so. It becomes evident when reviewing the literature that there are many variables to consider regarding timing such as the breed of the specific dog, genetic variation within the breed, and most likely developmental sequelae post gonadectomy/OHE.

There are no hard and fast rules with timing, but the literature that does exist can provide insights that help guide your veterinarian in their medical decision-making process.

Structural Health Concerns

One of the post-operation considerations your veterinarian will think about is that the hormones released by the reproductive tract play an integral role in bone growth and formation. Androgen hormones play a role in the closure of growth plates, and the removal of these hormones would allow for continued proliferation and elongation of the bone.

This would also mean that the joint configuration would not be optimized and could lead to other disorders, such as hip or elbow dysplasia, down the road. Large breed dogs have a longer growth period than small breed dogs, so recommendations based on a standardized age for all dogs does not take into consideration the growth stage of that pet.

For example, a study showed that male Labrador retrievers castrated at about 2 years of age had the lowest risk of cranial cruciate ligament disease (analogous to anterior cruciate rupture in humans) and elbow dysplasia. Also, to lower the incidence of hip dysplasia in female Labrador retrievers, spaying at 2 years of age was optimal.

In a study involving over 600 rottweilers, it was found that dogs spayed/neutered before 1 year-old were about 3 times more likely to develop osteosarcoma (a bone cancer) compared to intact dogs due to the role that estrogen plays in bone cells. However, it is worth mentioning that there are many confounding factors in these studies, one of which may be that the overall higher cancer risk in the spayed/neutered dogs may be due to longer life spans.

Another post-spay sequelae may be urinary incontinence. While this can often be medically managed throughout the life of the pet, it can often be a nuisance to pet owners at its start. Female dogs that are spayed are at greater risk for urethral-sphincter mechanism incompetence (which can lead to urinary incontinence) than intact female dogs.

It should be noted that breed size also plays a role in this process as well since large breed dog incontinence rates are approximately 9.12% versus small breed dogs at 1.37%. The literature states that occurrence of urinary incontinence halves if a dog is spayed after the first estrous cycle. Another article found that spaying before 6 months old increased the incidence of urinary incontinence by 0.68% on average, with the probability that developing it increased as the animal aged.

Summary of the Benefits of Spaying and Neutering Dogs

Clearly, when deciding when to spay and neuter your pet, your veterinarian considers a multitude of variables by weighing the newest research and taking into consideration your specific pet’s needs. Although it is tough to generalize the research, it can be deduced that females should not be spayed until 3-4 months of age to avoid urinary incontinence, and for many breeds, males can be neutered safely at any age above 6-8 weeks of age. There are always exceptions to the rule, however, and it is important to discuss your dog’s breed, inherent risk of developing certain disorders, and your goals for your pet’s longevity with your veterinarian.

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