post image

To Neuter or Not to Neuter – What You Should Know

Is neutering good for your dog or cat or is it dangerous? Are there adverse consequences to neutering? Most of us have been told for years that neutering is good and prevents many health problems, but are there negative effects of neutering? The answer is yes. We want to tell you what you may not know about the dangers of neutering.

I’m the Irreverent Veterinarian. I give my honest opinion about various controversial issues in the animal care world. I speak my mind and some might say I am honest to a fault. I tell it like it is. Some of what I say can be harsh but that doesn’t stop me – it can be hard to hear the truth. This is a topic some pet owners and some veterinarians may not enjoy.

If you ask nearly every veterinarian, veterinary technician, shelter worker, rescue group or anyone else in the animal care world, they will tell you that neutering your pet is a necessary procedure and your pet will be happier and healthier. About 80% of dogs and cats in the US are neutered.

Neutering is a general term that refers to removal of the testicles in males or ovaries and uterus in females. For male dogs and cats, the surgery to remove the testicles is called castration. For female dogs and cats, the surgery to remove the ovaries and uterus is called an ovariohysterectomy (OHE), commonly called spaying. This is a good time to mention a pet peeve of many (one of many). If a female animal had its ovaries and/or uterus removed in the past, it is SPAYED (pronounced SPADE or like played). It is NOT spaded! The verb is ‘to spay’ and the past tense is spayed (just add ‘-ed’ on the end like the majority of verbs. To play – past tense played.))

For decades the recommendation has been to neuter pets around the age of 6 months. There is no reason and no research that proves why this age is important. Apparently someone made it up and it caught on. It is likely an age when veterinarian felt the pets were old enough and strong enough to have minimal risks of anesthetic complications.

For the past decade or so early neuter has been suggested. This is primarily for animals in shelters for adoption purposes. The shelters want to ensure that the animals do not have litters after leaving. There is current and ongoing research that is showing some negative health effects of early neutering such as increased rate of urinary tract infections, urinary incontinence, hip dysplasia, and some behavioral issues.

Much more research needs to be done and the risk of pregnancy must be weighed against the benefit and take the negative health effects into consideration. There are also negative health concerns regarding neutering at later ages as well, including at 6 months.

Usually, the number one reason vets and others will say to spay your female pet dog (to remove estrogen) is to reduce the risk of mammary (breast) cancer. The overall risk, depending on the study, is about from less than 1% to 3% and up. If the dog is spayed before its third cycle (around 3 years of age) the risk can be reduced a little further. However, vets will usually say something like “if you spay your dog early you can reduce the risk of mammary cancer by 98%.” What they don’t tell you is the risk itself is very low. This means that about 1 to 3 out of 100 dogs may get mammary tumors. For dogs, there is a 50:50 chance they are benign. For cats, most are malignant.

There are also the obvious benefits of no testicular cancer, no uterine cancer, no ovarian cancer and no life-threatening uterine infection (pyometra).

Another claim is regarding positive behavioral changes. There is no reliable research that proves this is true. However, there is research that is starting to show that what vets have been telling pet owners isn’t true. For example, veterinary staff often say that more intact dogs roam, run away, display sexually inappropriate behavior (mounting and humping) and have a tendency toward aggression. Having the vet community admit that we were wrong or more information is needed is not likely to happen.

Obesity is another concern for neutered pets. As most of us know, it is very difficult to get a pet to lose weight after it has gained too much. Preventing obesity is the key and that means training the owners. I heard there is a study that hasn’t been published yet that shows how people can’t tell when their pet is overweight, even if it is obvious to everyone else.

Did you know that there are many European countries that recommend avoiding routine neutering of pets? And the country’s animal health authorities agree? And, before you think it, those countries do not have pet overpopulation problems.

Are Neutered Pets Happier & Healthier?

Another point – are neutered pets really happier and healthier? How does anyone know if they are happier? I recently talked to a vet friend of mine I have known for at least 15 years. We had never discussed the topic before. I told him I was writing this article and he became quite passionate that all dogs must be neutered. He brought up breast cancer and roaming. He also said that since they don’t have the constant pressure of reproduction they will be happier. WHAT!? Constant pressure? Female dogs come into heat about twice a year for up to 2 weeks or so. I tried to bring up the studies about orthopedic issues, etc. but he wouldn’t let me get a word in. I had no idea he was so pro-neuter. I decided to agree to disagree and plan to send him some studies at a later time.

Adverse Effects of Neutering

In the past several years there have been studies suggesting that there are significant adverse health effects when a dog is neutered. Some are breed specific so you will need to be careful on interpreting the study results. They may or may not apply to other breeds. Examples include:

– Noise phobia (thunderstorms, fireworks)
– Inappropriate sexual behaviors, like mounting
– Fearful behavior, particularly aggression

As a Veterinarian – Will I Neuter My Pets?

Personally, I am rethinking neutering my pets. I recently adopted a dog with a terminal disease. He has not been neutered and I don’t plan to. He is great. He has no problems and gets along great with my other two neutered male dogs. Another dog that I adopted a year ago came to me intact. I did neuter him per the rescue organizations requirements but noticed a lot of changes. He became shy and easily frightened. He didn’t play as much and he lost all his muscle definition. I didn’t really like the changes. For reproductive concerns, I will either remove the uterus and leave the ovaries for females and do a vasectomy on males. What is wrong with that?

I have participated in several overseas spay/neuter campaigns with different organizations. A group goes to different countries with vets and techs and neuters pets for free. During the last campaign, 2010, we met a farmer in the hills that did not want any more puppies but also did not want his dog to lose his testicles, probably due to machismo. Whatever. Anyway, I said to the group member with me that I could easily do a vasectomy and make both happy. The representative from the group refused. She said it is either castration or nothing. I was quite appalled. I have not done another campaign with any organization since then.

I will be honest. I would have to think long and hard about spaying my females. I would remove the uterus but leave in the ovaries and see how it went.

Are We Neutering Too Young

One question I have is ….are the pets too young when they are neutered? Do the hormones help the bodies develop like they have been shown to in people? For example, one study reported that there were 0 cases of cruciate ligament rupture in intact dogs but 5% in neutered males and 8% in neutered females.

Would allowing a pet to attain their full adult growth before neutering help minimize some of these risk? That has yet to be answered.

How About Other Options to Neutering

Instead of castration, another alternative is a product currently licensed as Zeuterin. Zeuterin contains zinc gluconate and arginine and approved for male puppies between 3 to 10 months of age. This will result in sterility by chemical disruption of the testicles. The dog will still have some testosterone after the procedure. The product is injected directly into each testicle. Veterinarians must take a 5-hour training course before being allowed to administer it. This product was first marketed in 2003 as Neutersol. In 2005, there were issues with the owners and manufacturers of the drug and it was no longer produced. The intellectual property was purchased by Ark Sciences, Inc. and production resumed in 2014 with a new name.

Vasectomy is another alternative. This will prevent overpopulation but allow dogs to maintain normal levels of testosterone.
Females can have a hysterectomy (have their uterus removed but leave the ovaries) and still have normal hormone function without the risk of pregnancy.

These may be options to full fledged neutering.

What Other Vets Think

This was an informal poll but I went to 6 vets to ask what they thought. I just wanted to present the balanced facts to these vets about what they may not know, give them a few days to research, then get their opinion on neutering dogs and cats. This is what I learned.

Final Thoughts on Neutering Pets

Based on all this information, I would suggest getting as much information as possible before making a decision to spay or neuter. Research on this topic is relatively new. The first significant studies started coming out around 2007. More studies need to be done to provide the best information. Some currently published studies are breed specific (golden retrievers, Labrador retrievers and vizslas) and it is unclear how this research will extrapolate to other breeds.

There are some other benefits to neutering. There may be a slightly lower incidence of mammary (breast) cancer but that has yet to be confirmed. There is a reduced risk of pyometra (an infection of uterus) because it is removed with the spay surgery, but this would apply to a hysterectomy and leaving the ovaries in place. As I mentioned above – some of the studies appear to be flawed that suggests many of the benefits to neutering. More unbiased research is needed.

More studies are needed on both dogs and cats and on a variety of breeds to really understand the impact of neutering on health. What we do know is that there are risks and consequences of neutering. The question is – how much risk and do the risks outweigh the benefits?
Here is the big question I really have. Should we be using the alternatives to neutering (hysterectomy and vasectomy) OR should we neuter when animals are considered full grown and mature (which can be 1 to 3 years of age depending on the breed). Would this minimize some of the adverse effects of neutering?

Is the risk of problems from neutering better or worse than euthanizing more pets? That is a tough question.

My opinion is that you need to research about the pros and cons of neutering. Speak to veterinarians or researchers. Try to understand why some people will refuse to accept that neutering isn’t all positive. Their main goal is to reduce the number of animals euthanized each year. But, you are concentrating on your individual pet. That makes a big difference.


The Irreverent Vet is a columnist that regularly contributes to The goal is to add a balanced and alternative view of some controversial pet issues. As happens with all of us, veterinarians can’t always say what they really think without offending some clients. This commentary allows vets to say what they think and give you, the pet owner, the opportunity to consider another point of view. All opinions are those of the Irreverent Vet and not the views of and are not endorsed by


Early Spay-Neuter Considerations for the Canine Athlete: One Veterinarian’s Opinion
© 2005 Chris Zink DVM, PhD, DACVP, DACVSMR
Extensively revised and updated – 2013
Canine Sports Productions –