What is the best age to spay or neuter your dog?

When is the best age to spay or neuter your dog?

This is a question that has been on a lot of veterinarians’ minds over the last couple of years. There have been some studies done that have had some interesting findings, particularly for golden retrievers and Labradors. I will try to present this new information to you, and highlight the risks and benefits of different options.

First, a quick review:

The medical term for spaying and neutering is “gonadectomy,” from the word gonad, meaning reproductive organ, and the medical suffix “ectomy,” meaning to surgically remove. In the female, the ovaries and uterus are removed. This is commonly called a “spay,” or more technically an ovariohysterectomy, or OHE. In the male, the testicles are removed. The common term is neuter, or castration.

Performing an OHE in a female dog is done to prevent unwanted pregnancies and diseases of the ovaries and uterus such as infection and cancer.

Castration of a male dog prevents unwanted breeding, and prevents infection and cancer of the testicles and prostate.

Gonadectomy in both males and females can help reduce unwanted behaviors like roaming (to find a mate), or aggression toward other dogs, and urine marking of territory.

In the USA most gonadectomies are done when a dog is 4-9 months old.

My overall advice is still to spay and neuter any dog that is not going to be part of a professional breeding program. The question is when is it the best time to do the surgery?

Let's talk about the small or medium sized dogs first. These dogs are not as prone to bone and joint diseases like larger dogs, so it is an easier question to answer. I am still recommending that we spay and neuter these dogs between 5-9 months of age.

Why? Because if we remove the females ovaries and uterus prior to her first heat cycle, we reduce the risk of mammary (breast) cancer a lot. Let's look at the numbers: females that have never had a heat cycle have a 0.5% chance of developing mammary cancer. If they have 1 heat cycle before they are spayed the risk increases to 8%. If they are not spayed and are over 2.5 years old the risk jumps to 40%.

For the small and medium breed males, there is no evidence as of yet to suggest that neutering between 5-9 months old has an effect on the development of bone and joint disease. This information might change with new studies.

The question becomes more complex when we start talking about larger breeds, particularly golden retrievers and Labradors.

For the males, if it is at all possible, I recommend that they are not castrated until they are at least 1 year old, or until they have reached skeletal maturity (fully grown). Testosterone, which is produced by the testicles when they are mature, has an important role in bone development. These large breeds develop differently if neutered before maturity.

One study showed that large breed male dogs neutered younger than 6 months old were 3 times more likely to tear their anterior cruciate ligament (ACL) in the stifle joint. This is one of the most common reasons for acute rear limb lameness in larger dogs, and it requires surgery to stabilize the joint and keep the dog pain free.

This study also showed that male dogs neutered younger than 1 year old were twice as likely to develop hip dysplasia, a condition where the hip joints don't fit together well, and leads to osteoarthritis as they age.

It is important to note that this study was on golden retrievers ONLY. There is no information YET to suggest that this applies to other breeds.

With regard to prostate and testicular diseases, neutering a dog at any age can prevent these problems, provided they haven't already occurred.

It also must be remembered that if you have a male dog that is sexually mature (6 months or older), they are able to breed with a female, so it is your responsibility to keep them under control to prevent unwanted puppies. This can be difficult if you own a female that is not spayed. Keeping a male dog that is not castrated for at least 1 year may not be possible for everyone.

The most complex group is the large breed females. As veterinarians, we are walking a fine line between preventing serious life threatening diseases and preventing serious bone diseases. We want to do the OHE early enough to reduce the mammary cancer risk as well as serious uterine infections (pyometra), but not so early that we increase their risk for orthopedic (bone) problems and other forms of cancer.

Based on current evidence, my advice would be to spay large breed female dogs between their first and second heat cycle.

The first heat cycle can occur any time between 6 and 9 months old.

Remember, it is possible for a female to become pregnant on her first heat if she breeds with a male. As an owner, you have to be aware of this and be responsible for preventing unwanted puppies. If you don't feel that you can do this, it is better to perform the OHE before the first heat cycle.

Overall, more studies are needed on this topic. As we discover new information, recommendations will probably change. Any disease like cancer or hip dysplasia is complicated and patient genetics and environmental factors are likely to be equally as important as when we perform gonadectomy.