What is the Right Age to Spay or Neuter Your Pet?

There’s a lot of controversy surrounding when the best age is to spay and neuter your pet. Some studies suggest that neutering your pet too early can cause cancer, muscle, or bone issues. Other studies have shown that your pet actually lives longer if they have been neutered.

This article will sort through the medical studies available along with our experience, and we’ll give our opinion about whether spaying is best early or late. And to help you make an informed judgment, we’ll also show you evidence from both sides.

Why Do We Neuter Our Pets?

In the United States, it is an unfortunate fact that we put to sleep somewhere between 1.5 and 2 million dogs and cats annually. These numbers don’t include deaths from car accidents, predation, disease, or starvation.

Our country has tried to control the skyrocketing pet population by overfilling our shelters for years. Shelters trap and release animals after neutering them, and sometimes they are forced to humanely end the lives of young, healthy animals that would make great pets.

So by neutering our four-legged friends, we can prevent them from reproducing and adding to the already overcrowded national crisis.

Support for Not Spaying/Neutering or Delayed Neuter

The decision to spay or neuter your animal companion can be highly personal. In fact, UC Davis released a few studies supportive of delaying the time when a dog is neutered. These are the articles that they published:

That said, these are studies that looked at past events and have attempted to assign a relationship between certain conditions. These conditions range from, for example, hip dysplasia (hip dislocation), risk of cruciate ligament (connective knee tissue) tears, cancer such as osteosarcoma (bone cancer), among others.

The research teams took this data collected from past patients and compared these conditions to animals that either had or hadn’t been spayed/neutered. Their papers said the chances were greater for spayed and neutered dogs to develop abnormal growths, muscle and bone problems, as well as increased chance of sickness or infection.

Support for Spaying/Neutering or Early Application

Some pet owners want to give their sidekicks the best shot at a long life as possible, and there’s plenty of evidence to support that. For example, the University of Georgia conducted their own study as an alternative to UC Davis’s findings. They concluded that:

  • The average age of death for dogs that weren’t spayed/neutered is 7.9 years
  • The average age of death for neutered/spayed dogs is 9.4 years
  • Males that had been altered lived longer by 13.8%
  • Females that had been altered lived longer by 26.3%

These papers showed that altered dogs were more likely to die from immune-mediated disease and abnormal growths, and they were “dramatically” less likely to die from infectious disease, trauma, vascular disease, and degenerative disease. They were also less likely to have mammary (milk-giving organ) cancer.

Banfield veterinary hospital is a nationwide animal hospital with a computerized medical record system shared across the country. They release yearly reports on data analysis from millions of dogs and hundreds of thousands of cats. Banfield did claim that spayed or neutered dogs and cats live longer than those that aren’t, however they didn’t release exactly how they determined that.

A Brief Critique of the Literature

The UC Davis articles were written after the fact with patients that had been referred to their state-of-the-art facility. The studies were done to see how early neutering affects conditions such as hip dislocation and risk of knee ligament tears, as well as cancers such as osteosarcoma, among other commonly associated conditions. These four papers were given credibility based on the reputation of the facility that oversaw the studies. But there are several major concerns that question how sound the assumptions made by these papers.

The research population was biased.

  • The cases that were considered for these studies were patients that were referred. This means they had pathology that was not common. Referred patients are not usually cases that an everyday vet would take on.
  • There are many kinds of cases that a general practitioner would manage. Those cases aren’t considered in the research because they never went to the referral center. For example, an everyday vet may treat a pyometra, which is a life-threatening uterus infection. Pyometra is only seen in dogs that are not spayed. If these dogs were spayed, a pyometra would’ve been prevented because the uterus is removed. No uterus, no pyometra. The treatment for pyometra is usually handled by primary care, so the patient wouldn’t be referred. UC Davis research teams wouldn’t have had the data available about how many dogs that weren’t spayed that developed pyometra. This data would be valuable in deciding the cost to benefit ratio for whether or not to spay early or late. And it’s also this kind of lack of data can skew the research information gathered. It makes it seem like some conditions are more or less common than others.
  • People who cannot afford to spay or neuter their pets probably wouldn’t be able to afford specialty care at such a facility as UC Davis Teaching Hospital. This means there are more animals that are spayed and neutered making it to the referral center. These unaltered animals would be excluded from the research then, which might’ve skewed the data.
  • There were other factors that were not controlled in these cases. These were studies taken from past cases, not active ones. Being obese, genetics, activity level, nutrition, etc. weren’t considered as possible variables in hip dysplasia (hip dislocation), for example. The only thing considered was whether or not the animal was spayed or neutered.

The data could be interpreted in different ways based on the sequence. The date a particular condition begins could provide valuable insight into determining if there’s a relationship between that condition and a spaying/neutering. For examples, it should be considered whether an animal was spayed or neutered after being diagnosed with hip dysplasia (hip dislocation) vs being spayed or neutered first, then developing hip dysplasia (hip dislocation). These studies only considered whether or not a spayed or neutered animal had a specific condition, and cause and effect based solely on association isn’t useful to a credible study.

These studies only looked at certain breeds. If what they found is true for a particular breed, we cannot generalize this information and assume it will be seen in other breeds.

Finally, comparatively, group sizes were very small. It’s very important that group sizes are large to reduce the chance of random cases influencing the accuracy of the studies.

The University of Georgia study that was performed used a much larger sample size of over 40,000 dogs. That said, this too, was a study based on past cases and didn’t have controlled environments in which to conduct research. This paper suggests that no comprehensive study has ever been made on the relationship between mortality and reproductive capability (whether spayed/neutered).

UC Davis referred to this paper, mentioning how the University of Georgia also found that sterilized dogs died of cancer. What they failed to consider, though, was that these dogs were also found to live longer overall. In older animals, cancer becomes much more likely. They found that sterilized dogs were more likely to die from neoplasia (mast cell tumors, lymphoma, osteosarcoma, transitional cell carcinoma) and immune-mediated disease. They also found that sterilized dogs were less likely to die from mammary (milk-giving organ) cancer.

Do Your Research

We encourage you to take the time to read each of these articles and form your own informed opinion. We also believe that the data we got from these studies isn’t sufficient to make assumptions about early sterilization and higher risks of disease.

But we do know some things for certain.

Approximately 80% of female dogs in the United States are spayed. Mammary (milk-giving organ) cancer is found in about 4% of the population. It mainly affects dogs that haven’t been spayed.

In dogs that have been altered, the research suggests that the risk of osteosarcoma (bone cancer) is 0.2%. The risk of mammary cancer greatly outweighs the suggested risk of osteosarcoma. This puts a dog that hasn’t been spayed or neutered at a higher risk of disease than that of a sterilized dog.

In total, if you consider the incidence of all of the diseases seen in sterilized dogs, the total is merely 3% vs the chance of a female dog that hasn’t been spayed of developing pyometra (24%) or mammary cancer (20%).

Summary of Recommendations

Depending on the size and breed of the animal, the appropriate age to spay or neuter can change. Refer to the following chart below for our recommendations.

Discover if spaying or neutering is right for your pet at Vet’s Here.

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