When to Spay or Neuter?

There has been considerable discussion lately about the ideal time to spay or neuter your pet. Here's a run-down:

None of the following applies to cats.

In cats, there is almost no reason not to perform surgery at or before 5 months of age. There is minimal evidence of increased risks of cancer or orthopedic disease to consider, and that only leaves the behavioral aspects, which clearly indicate early surgery as the best option.

Now on to Dogs.

So what is the issue? This issue is that there is evidence that spaying or neutering dogs (hereafter we will just say “neutering”) can increase the incidence of various cancers and orthopedic problems, and the increase depends on the age at which surgery is done. Several studies show an increased risk of lymphoma and hemangiosarcoma in neutered females regardless of what age.

There have been several scientific papers written that have received quite a bit of attention in the popular press. A 2014 study by Hart et al examined spay/neuter age in Golden and Labrador Retreivers. They found that neutering increased the incidence of joint problems from a base-line of 5% to 10% in both sexes. Another 2020 paper by Hart et al actually included a chart showing “ideal” surgery ages broken down by breed. There are many other studies as well.

The problem is, when you look at all the data, how it was collected, analyzed, and look at the sample sizes and populations involved, the data are

a) far from overwhelming,

b) not consistent between studies.

c) there appear to be big differences between breeds, and this muddies the waters considerably when dealing with cross-breeds (and yes, doodles are cross breeds).

d) many of the studies have flaws in how data was collected, sample sizes, how the data was statistically analyzed, and lastly most of them make no effort to control confounding bias.

Confounding bias is particularly interesting. For example, take orthopedic disease. There does seem to be an effect where neutered dogs are more likely to have orthopedic problems than non-neutered dogs, but it is also evident that in general neutered dogs are more likely to be over-weight than non-neutered dogs. Is the problem related to the surgery or the Alpo? We don’t know. Both are plausible. Also, most studies show an increase in life span in neutered dogs. Old dogs get more cancer. How does this affect the observed rates of cancer? We don’t know.

A few things are fairly well-established.

Not many people argue with the data on mammary cancer. The data on mammary cancer are quite old, and are consistent between studies. In general, a never-neutered female dog has about a 1 in 4 chance of developing mammary cancer. That’s huge. Spaying before the first heat reduces the chances to near zero. If they have even one heat before spaying, the incidence climbs to 1 in 14. After several heats, it is just like they had never been neutered at all. Spaying early clearly protects against a very common cancer.

Not many (rational) people argue with spaying being protective against pyometra, a life-threatening uterine infection. Data show that an unspayed female dog has about a 1 in 4 chance of developing this infection at some point in her life. The data range from 10% to 50% depending on breed. Age when neutered does not matter in this case.

Neutering does seem to increase the risk of orthopedic disease in both genders in at least some breeds. we're talking Hip Dysplasia, Elbow Dysplasia, and Cruciate Ligament problems. It is debatable over how much it increases the risk, and in which breeds it matters.

Cancer risk is a little grey-er but most folks would agree there is some effect. It is quite consistent that neutering can increase the risk of non-mammary cancers like osteosarcoma, lymphoma, and hemangiocytoma, but the effect varies between breeds and cancers and neutering has actually been shown to be preventative in some breeds and some cancers.

However....

One issue that the scientific studies fail to address at all is the behavioral aspects of delayed neutering. There are two main reasons we neuter dogs in the first place: to prevent unwanted reproduction, and to reduce undesirable behaviors. Especially in males, these undesirable behaviors can be deal-breakers, and their incidence is much much higher than that of orthopedic disease or cancer. In fact, most un-neutered male dogs will exhibit at least one of them:

urine marking
fighting
aggression
roaming the neighborhood
escaping
humping
and general orneriness.

Question:

Is it worth gaining a 10% protection against a cancer that only strikes 1 in 200 individuals for a 75% chance of that individual developing undesirable behaviors?

Answer:

It depends....

So it becomes a trade-off, balancing a decrease in some less common health problems against an increase in some very common behavioral problems. We also balance the protection from mammary cancer which occurs at a high (25%) incidence and pyometra (also 25%) against a modest (maybe 10%) decrease in the incidence of relatively rare cancers (lymphoma, hemangiosarcoma, osteosarcoma) that occur at a single-digit incidence.

As we said earlier, it’s highly nuanced.

I maintain that anyone (I’m talking to you, breeders) who has a definite, strongly-held opinion that there is one ideal time to perform surgery doesn't fully appreciate the complexity of the situation. The more you know, and the more you research, the more it becomes clear that the question of when is the best time to spay or neuter is highly nuanced, involves both medical and behavioral issues as well as family issues, and there are no absolute answers to it.

In general...

For most patients, most clients, most of the time, 5 months is a good time to neuter dogs of both genders.

There are other acceptable answers, and as long as you have a well-though-out reason for thinking that way we will support your choice.