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Neutering your dog’s at 6 months: The Facts

On neutering, you will be hard pressed to find a vet today that would recommend anything but neutering your pet early in their life, normally around six months. The reasons given are always the same, prevent unwanted babies and long term health benefits including a reduction in cancer.

On neutering, you will be hard pressed to find a vet today that would recommend anything but neutering your pet early in their life, normally around six months. The reasons given are always the same, prevent unwanted babies and long term health benefits including a reduction in cancer.

But unlike your appendix for example where it’s absence is not noticed in your daily routine, your reproductive (or sex) organs play a whole host of hormonal roles that stretch far beyond the manufacturing of babies. Like dry food, parasite control, annual boosting and casual steroid shots, these things are not without consequence for the patient and too rarely are these consequences ever discussed with the owner. It is not enough that we are told things are perfectly harmless. We must go into the decision with eyes wide open.

So here’s what we know of neutering dogs early in their life. The implications for your pet and society as a whole are then discussed below. It’s a whopper of an article, maybe grab a cup of tea first! This would normally be two articles but if I chop it in half people will be left with too many questions. Please leave emotion at the door and your comments below!


In male mammals the gonads are the two testes, and in females the gonads are the two ovaries.


The gonads are best known for making gametes (single celled germ cells) which is sperm in males and eggs in females. These two cells then get it on inside the female and make a baby. Most of us have that down pat.

But the gonads also produce a variety of hormones including the female sex hormones estrogen and progesterone; and the male hormones including testosterone and androsterone. However men necessarily have some of the female hormones, and women some of the male hormones.


While sex hormones in males and females function largely in the whole “sex” business from conception to baby birth, they also play pivotal roles in the maintenance of body muscle and bone growth.

We see testosterone’s dramatic effects in lanky 13 year old males. It controls all the typical puberty bits in males such as the less useful growth of the adams apple, facial and body hair to the very much more useful height and muscle mass of the individual. As adults testosterone continues to function in maintaining muscle strength and mass, and it promotes healthy bone density. It also reduces body fat (one reason why some spayed pets can put on weight).

Estrogen too functions in skeletal growth. At puberty, estrogen promotes skeletal maturation and the gradual, progressive closure of the epiphyseal growth plate (plates of cartilage at the end of bones, which are responsible for laying down new bone). Estrogen also functions in maintaining the mineral acquisition by your bones.


Neutering or ‘spaying’ a female animal involves removing the womb and ovaries (an ovaro-hysterectomy). Males are castrated whereby the testicles are surgically removed. This is done before dogs come into puberty (i.e. start producing sex hormones for the first time) which is very approximately 6 months in males and around 9 months in females, though breed and body size play large rolls here. General advice from the majority of veterinary circles is that responsible dog owners neuter at 6m months. In other countries it is much earlier. Both operations are carried out under general aesthetic.


The number one reason for removing the sex hormones is to prevent unwanted breeding, hence folk at the front line of mopping up all our unwanted fur babies are very big fans. The major health benefit constantly cited is to prevent the possible occurrence of testicular cancer, peri-anal cancers and ovarian cancers in dogs and cats. Other reasons often cited is the spread of inferior genetic traits and to reduce problematic behaviour including male-male aggression around females in heat and the roaming behaviour of both males and females when love is in the air.


The early neutering of dogs is not without it’s side effects or critics, and I’m certainly one of them. But please, before the heavily stressed and over-worked shelter staff post up about overpopulation problems (I spent a couple of years in them too), lets look at this this issue with less emotion and more science.


If we ignore the fact that gonadal cancers are rare enough in a general population and that dogs recover very well from testicular cancer following diagnosis and castration, by removing the gonads in developing animals you certainly prevent the possible occurrence of gonadal cancers such as testicular and ovarian cancer. However, ironically, while these possible cancers of your pet will be avoided, numerous studies show that removing the sex organs early in the developmental period of an animal causes cancer in your pet, just not in their testes or ovaries.

A study in the Journal of Veterinary Internal Medicine, compiled over 13 years found that “… neutering dogs appeared to increase the risk of cardiac tumor in both sexes”. The results showed that spayed females were five times more likely to to suffer tumours of the heart than intact females

In another study spanning 14 years of research it was concluded that sterilisation increased the risk for bone cancer in large breed pure-breds twofold.

Upon further investigation using male and female Rottweilers spayed or neutered before one year of age, both sexes were found to be significantly more likely to develop bone cancer than intact dogs with early sterilisation bestowing a staggering 25% likelihood of bone cancer in your Rottweiler.

(Cooley et al. 2002,

It’s often stated that neutering a male dog will prevent prostate cancer but some authors refute this on the basis that ” non-testicular androgens exert a significant influence on the canine prostate”. The College of Veterinary Medicine at Michigan State University found “…castration at any age showed no sparing effect on the risk of development of prostate cancer in the dog.”


All these considered, it’s hard to argue the cancer benefits to neutering early or you end up playing the whole “I see your very slight chance of testicular cancer and raise you a certain increase in bone and heart tumours”.


Testosterone and estrogen play pivotal roles in the development of your muscles and bones. It stands to reason that if you remove testosterone and estrogen from the vital and dramatic puberty growth phase there will be consequences to that individual’s height, muscle mass and bone formation of the individual, compared to an intact animal of the same size and breeding. Studies show this to be absolutely the case.


A study by Stubbs and Bloomberg (1995) set out to answer the following theory: Estrogen tells the growth plates to stop. Thus if you remove the estrogen-producing organs in immature dogs, female and male, you could expect cause growth plates to remain open and the dog to grow longer bones. They divided dogs and cats into three groups. Group one was neutered at 7 wks, group two at 7 months, and group three remained unneutered. They found that “early spay/neuter may result in a slight increase in adult height”. The earlier the spay the taller the dog. Other authors found similar findings (Salmeri et al 1991).

Preston Stubbs, DVM & Mark Bloomberg, DVM Seminars in Vet Med & Surgery, Small Animal, Volume 10, No 1 Feb 1995 Dept of Small Animal Clin Sci, Univ of Florida

Katherine Salmeri, DVM, Mark Bllomber, DVM, Sherry Scuggs, BS, Victor Shille DVM, Journal of American Vet Med Association, Volume 198, No 7 1991


Thus with no estrogen to shut it down, these animals can continue to grow and wind up with abnormal growth patterns and bone structure. This results in irregular body proportions.

Grumbach (2000) quotes Chris Zink, DVM to explain the problem with neutering males and females early and cruciate rupture – “For example, if the femur has achieved its genetically determined normal length at 8 months when a dog gets spayed or neutered, but the tibia, which normally stops growing at 12 to 14 months of age continues to grow, then an abnormal angle may develop at the stifle. In addition, with the extra growth, the lower leg below the stifle likely becomes heavier (because it is longer), and may cause increased stresses on the cranial cruciate ligament.”

This is verified with a study by Slauterbeck et al. (2004) who found that spayed and neutered dogs had a significantly higher incidence of ACL rupture than their intact counterparts, regardless of breed or size.


A study by the Cornell University’s College of Veterinary Medicine and published in the Journal of the American Veterinary Medical Association showed that both male and female dogs sterilized at an early age were more prone to hip dysplasia.


When one organ is removed, others will suffer and spayed and neutered Golden Retrievers are proven to be more likely to develop hypothyroidism.

Panciera DL. Hypothyroidism in dogs: 66 cases (1987-1992). J Am Vet Med Assoc. 1994 Mar 1;204(5):761-7

Glickman L, N Glickman, and R Thorpe. The Golden Retriever Club of America National Health Survey, 1998-1999. Available online at


Early neutering increases the risk of urinary incontinence by 4-20%


Very early neutering increases the risk of disease in dogs. A study of shelter dogs conducted by the College of Veterinary Medicine at Texas A&M University concluded that infectious diseases were more common in dogs that were sterilized at less than 24 weeks of age.


I can’t find a study to verify this, I can only testify to what groomers are repeatedly telling us, that desexed dogs have very woolly coats, commonly called “spay coat”. It seems to be an overproduction of the undercoat but until more is knows, this is anecdotal.


Dr. Karen Becker is now a famous veterinary advocate for more thought to be brought back in to the dog world. Her YouTube video last year on neutering and article on same subject gave me the bones of this article. The video received an enormous amount of support but also scathing criticism. Since then Dr. Becker has released another video on the subject explaining her thoughts on the whole affair. She breaks down in the middle of it when she thinks about the number of animals she has harmed with her previous advice. Worth a watch.

To quote Dr. Becker:

“As responsible members of society, we owe it to our communities to proactively protect our intact pets from unplanned breeding at all costs. We must hold ourselves to the highest standard of reproductive control over the intact animals we are responsible for.

Clearly, there are health benefits to be derived from waiting until after puberty to spay or neuter your dog. However, there are also significant risks associated with owning an intact, maturing pet.

How seriously you take your responsibility as a pet owner is the biggest determining factor in how risky it is to leave your dog intact until he or she matures. If you are responsible enough to absolutely guarantee your unsterilised pet will not have the opportunity to mate, I would encourage you to wait until your pet is past puberty to spay or neuter.

If you are unable to absolutely guarantee you can prevent your dog from mating and adding to the shameful, tragic problem of pet overpopulation, then I strongly encourage you to get your animal sterilized as soon as it’s safe to do so”.

It is interesting to note that some vet organisations agree with Dr. Becker. While the American Veterinary Association pushes for early neutering there are some European Veterinary Associations that defend the view that “when reproduction is not an issue, then neutering, particularly of dogs, should be decided on a case-by-case basis…”

In my opinion it is quite clear that neutering your dog early, before he / she is a fully formed, mature adult, comes with very significant health concerns. The best advice from a health perspective would be to put off neutering your pet until after puberty, which is at least a year, though some large breeds are still maturing at two years of age. And for all these major health benefits in your dog, all it takes is a little responsible pet ownership during the 3 – 6 month danger time. Sadly however, looking at just Ireland’s dogs, responsibility and dog ownership do not go hand in hand.

If aliens were to arrive in Ireland to study the success of sterilising dogs at 6 months and population control they would be forced to conclude that sterilisation does not work. We are the puppy farming capital of Europe. We have over 400 groups (shelters, pounds and charities) mopping up a portion of the strays. We are a nation of 4 million which killed 25% more more pet dogs than the entire UK (63mil) in 2010. We have a totally unregulated greyhound industry that slaughter many thousands more dogs each year with tax payers money. And they keep coming.

Clearly the issue of population control goes far beyond neutering or not. We have a desperately underfunded animal welfare system and our legislation protecting animal rights and welfare via heavy penalty fines and jail time is impressive for it’s almost total absence. On the other hand Sweden has 13 million people and only one pound. Lose your dog once there it’s a day’s wages. Lose him twice it’s a week’s wages. Lose him three time’s and he’s gone. This is all backed up with very tough welfare laws. Over there dog ownership is not so much a right as a privilege.

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