Hypomylenation in Weimaraners : The Final Shake Down

20140307_200308-MOTIONThis is a long entry for me. I realize that not many people stick with things past the third paragraph. Give it a shot though, I have a lot to say.

On Jan. 7 of this year I received an e-mail from Dr.Duncan, a scientist we’ve worked with for many years. I think it is 12 years, maybe 8. I can’t remember exactly. His studies included identifying the genes leading to hypomylenation in Weimaraners. Having experienced the disorder in our lines, we’d sent DNA to his study.

If you felt you were shorted in the “science brain” department, you probably were. Whatever you missed out on was given to Dr. Duncan. He has put it to good use. I could write a 30 page history paper in less than a week in college, and get an A+. I was always unimpressed with myself. I knew it wouldn’t change the world.  I wished I could have been a scientist but the math requirements were too rigorous for my bodacious-journaling brain.

Dr. Duncan studied hypomylenation in Weimaraners for a specific reason. Hypomylenation involves either the regeneration or late generation of the myelin sheath on the end of nerves. In Weimaraner babies, when this happens, it causes intention tremors. These tremors lessen to normalcy or almost normalcy by full adulthood. The scientific benefits for studying this as it relates to human nerve disorders is obvious.

“Novel mutations in myelin and myelin-associated genes have provided important information on oligodendrocytes and myelin and the effects of their disruption on the normal developmental process of myelination of the central nervous system (CNS). We report here a mutation in the folliculin-interacting protein 2 (FNIP2) gene in the Weimaraner dog that results in hypomyelination of the brain and a tract-specific myelin defect in the spinal cord. This myelination disruption results in a notable tremor syndrome from which affected dogs recover with time.”

As a Weimaraner breeder, our trade-off for contributing DNA would be a bench test identifying dogs who are carriers. Some breeders also donated euthanized affected puppies to the study. We were never able to make that sacrifice, knowing the majority of them would go on to have normal lives.  However, I have a lot of respect for their decision. Discovering you have shaky puppies is difficult enough without also making the decision to euthanize and donate them.

Our first shaky puppy happened in our first litter in 1997. We had them off and on periodically through the years. We were naive at first. We though the issue stemmed from a nutritional deficiency during pregnancy. After a few phone calls, a long time breeder explained the situation to me. Not a lot was known about it.

We steadfastly outcrossed to other genetics, believing that if it was a common recessive trait, we would breed away from the problem. It worked, sometimes. Even with breeding completely unrelated dogs, there is still a down-the-line lottery effect for inheritance.

I am sure some of my breeder friends are already fidgeting in their chairs. It’s difficult to talk about risks you take when you put purebred dogs together. The fact is this: Any two dogs you breed together can create any number of 12 genetic problems existing in all dogs.  If you’ve bred dogs long enough, you realize the genetic bite on the ass is going to come in the form of something you never saw coming, the thing you couldn’t conceive of, or even test for.

We moved forward with our breeding program even with the risk we’d get shakies. Dr. Duncan asked me why I bred these dogs when I knew the syndrome it was a possibility. I remember the perfunctory pause in our phone conversation when I said, “My dogs have a low incidence of HOD, immune problems, allergies and a low incidence of bloat compared to what I’ve heard others’ talk about. At least with shaky puppy, we know they are affected. It is a difficult realization, but we know what it is. It doesn’t randomly sneak up on you when your dog is 12 weeks old, or 5 years old, or later.”

I wouldn’t pretend it is a perfect argument. I always felt if we eliminated every dog who could “potentially” produce the problem, we’d only be inviting some other issue into our line that you couldn’t put a checkbox next to.  Entire breeds have nearly met their ruin by conscientious breeders on a witch hunt to eliminate all carriers of a problem out of the entirety of a gene pool.

We donated DNA from generations of carriers, and thankfully, DNA from shaky puppies we’d placed in loving homes. I am grateful to those individuals who took the time to send DNA to the study only at the encouragement of their nutty dog breeder.

Through funding issues and other set-backs, Dr. Duncan and other researchers still moved forward with their studies. I had, in my mind, given up on the idea that a bench test would be a possibility in the near future. It didn’t seem like they needed very much money to finish their research, but it was more than I had free to donate. I thought about them from time-to-time and soon five years had passed.

Jan.7 was a Tuesday morning. Dr. Duncan’s e-mail was concise. He let me know the test for hypomylenation was available. He also let me know that this was the final correspondence concerning the study.

I was ecstatic. I read all of the websites and the formal scientific paper they released on the years of research they put into identifying the DNA marker. It is several pages of great information. If you’d like to read it, click here to download the PDF. It is 1.1 MB.

The most outstanding part for me was the acknowledgements section which mentions my name specifically. I don’t point this out as a measure of ego, but as a measure of humility. My dogs and I had the opportunity to make a difference.  The frustrations we felt and the dogs who struggled made a real contribution. There are a lot of people who helped, but we did have a little part in finding an answer.

The next task was to start testing my dogs. The first one out the door was Gunnie. He has 56 puppies that exist between litters we’ve had with him, and what other breeders have produced using him as a stud. He came back N/N (carrier/affected negative). Gunnie had a 25% chance of being a carrier which is enough of a chance not to take it for granted that he came back N/N.

After all of my tests came back, I had a rude shock.  The sire and dam combination we bred on 12/25/13 and 12/27/13 was between two carriers. Ducky had a 50% chance of being a carrier. Uma definitely was not expected to be a carrier. I hoped that maybe she wasn’t pregnant. I knew she likely was.

If I charged past you in the hallway at work after I found out about Uma’s carrier status, just be glad I didn’t barf on you. The irony was so thick for me in that moment, you could have cut it with a knife. I had a pregnant dog who had shaky puppies. Statistically there’s a small possibility that none would show up, but it isn’t likely we would be so lucky. The sun doesn’t shine on recessive genetic issues that way.

I knew we would get shaky puppies, and indeed we have. Three of my six beautiful girls are affected and one boy. 50% of the litter. You may offer the advice that I could have spayed Uma when I found out this news. I am not strong enough to do that to a litter of puppies. I realize it happens every day, but they’re my dogs, even before they’re born.  You may judge me accordingly.

Champaign Wishes & Dog Bone DreamsThe bobbles appeared in a pronounced way on day 11 of their life.  The only consolation to be found is that they are they are the very last ones, ever. My mind has gone over the “what-if” scenarios as far as the timing is concerned. But they’re living things and there are no guarantees for them, or me, or any of us, that perfection can be achieved.  If there is a lesson or a take-away from the situation, let it be that you should never take it for granted that your dog isn’t a carrier. Even though only 4% +/- of the Weimaraner breed are carriers, knowing is ultimately better than being surprised.

Being a carrier is not the end of the world. It gives breeders a chance to know what the next step is in finding the right girlfriend or boyfriend for their dog. Irish Setter breeders have virtually eliminated progressive retinal atrophy from their breed with this scenario. Don’t breed carrier dogs to each other, and your problem will solve itself in three generations.

Mac’s results came back as a carrier. It was almost as much of a surprise as Uma coming back as a carrier. At least we know. I have to make sure his girlfriends are not carriers. This is the gift that was meant for those who helped with the study, or have the issue in their line. I intend to use that knowledge with the spirit for which it was intended. We had planned on breeding Mac to Piper, who also turned out to be a carrier. While it disappoints me we can no longer breed the two, it is truly empowering to have this knowledge.  Both of them will be bred to worthy mates who are not carriers.

I still feel sick. My four little pups have a bouncy and bobbling road ahead of them. Another breeder friend of mine reminded me that we are probably the most knowledgeable people available to take care of them, and get them what they need. They need love, food, understanding, and to be treated like healthy strong dogs. In their minds, they don’t really see a handicap. It is only painful for us to watch and keep our fingers crossed that the journey to normalcy will be quick.

Adventures in Canine Artificial Insemination : Inaugural Edition

Bowl Of PuppiesModern veterinary practices make using stud dogs, in other parts of the country, much more accessible than in the past. In the old days, if you lived in Colorado and wanted to to breed your female to a stud in Florida, you either risked shipping her or planned 10 days off from your normal life to get the mating done.

We are lucky. We have never had to ship a female and I have yet to take a road trip for a mating. Colorado is one of the best places to be a dog breeder. We have Colorado State University veterinary school, along with many dog reproduction specialists also called Theriogenologists.  http://en.wikipedia.org/wiki/Theriogenology .  Don’t ask me to pronounce it.

Dr. Burns of Fort Collins is our canine reproduction specialist. We started visiting his clinic back in 2001, originally for semen collection and storage. Since then, we’ve done collections, fresh extended artificial insemination and frozen semen artificial insemination, among a few other things.

We did most of our initial artificial inseminations using the fresh-extended method. The dog is collected, his contribution is put into “hibernation” and is mailed over-night to the destination vet clinic. The benefit of using this method is the stud dog owner is not required to have frozen semen collection facilities near by. Any vet of relative skill and ambition can do the collection, add the preservative and send it off by FedEx.

There are a few different companies offering the preservative and shipping boxes. I am convinced the preservative can skew puppy genders one way or another. Depending on who we used, the litter was either almost all male, or all female. Granted, I try not to be bias toward one gender, but an even split is highly desirable.

Jane’s artificial insemination fell into this category. Her boyfriend lived on the east coast and the clandestine affair at Dr.Burns’ office was to take place on Jan.7. January is the coldest month of the year in Colorado and in most parts of the United States.

When the sample arrived in Fort Collins, Dr.Burns called me himself to let me know the entire collection had been frozen solid in transit. “There’s a problem, the whole collection froze, what do you want me to do?”

“Are there any still alive? Any at all?” I asked.

“It might be 25, maybe 30 percent motility It’s not looking good.”

Jane came into season every nine months so I was not thrilled with the idea of waiting until September to try again.  Randomly frozen sperm-cicles were not part of the plan.

“If there’s anything moving, do the A.I. What’s the worst that could happen?”

Dr. Burns didn’t argue with me. Jane had a surgical artificial insemination, and I drove up to Fort Collins to bring her home.

The answer to my not-so-rhetorical question is, the worst thing that can happen is the dog does not get pregnant.  This means $1,000 in shipping, progesterone tests, gasoline and semen collection kit, etc. all goes down the drain.

Jane was definitely pregnant though. It didn’t take long for her to swell up like whale. In fact, she ended up having 11 puppies by c-section in March. The caveat would be that nine of the 11 puppies were male. I wonder if the unauthorized freezing process did something to all of the girl sperms? We will never know. Jane was sure a trooper through the whole thing.

Dr. Burns still tells this story to his clients. It was a small wonder Jane conceived, not to mention delivering 11 puppies.

Next “Adventures In Canine Artificial Insemination” article –  Running around Denver like a crazy woman: How timing is everything in dog breeding!

Long-term health risks and benefits associated with spay/neuter in dogs

By Laura J. Sanborn
April 1, 2007

INTRODUCTION

Dog owners in America are frequently advised to spay/neuter their dogs for health reasons. A number of health benefits are cited, yet evidence is usually not cited to support the alleged health benefits. When discussing the health impacts of spay/neuter, health risks are often not mentioned. At times, some risks are mentioned, but the most severe risks usually are not. This article is an attempt to summarize the long-term health risks and benefits associated with spay/neuter in dogs that can be found in the veterinary medical literature. This article will not discuss the impact of spay/neuter on population control, or the impact of spay/neuter on behavior. Nearly all of the health risks and benefits summarized in this article are findings from retrospective epidemiological research studies of dogs, which examine potential associations by looking backwards in time. A few are from prospective research studies, which examine potential associations by looking forward in time.

SUMMARY

An objective reading of the veterinary medical literature reveals a complex situation with respect to the long-term health risks and benefits associated with spay/neuter in dogs. The evidence shows that spay/neuter correlates with both positive AND adverse health effects in dogs. It also suggests how much we really do not yet understand about this subject. On balance, it appears that no compelling case can be made for neutering most male dogs, especially immature male dogs, in order to prevent future health problems. The number of health problems associated with neutering may exceed the associated health benefits in most cases.

On the positive side, neutering male dogs;

  • eliminates the small risk (probably <1%) of dying from testicular cancer
  • reduces the risk of non-cancerous prostate disorders
  • reduces the risk of perianal fistulas
  • may possibly reduce the risk of diabetes (data inconclusive)

On the negative side, neutering male dogs;

  • if done before maturity, increases the risk of osteosarcoma (bone cancer) by a factor of 3.8; this is a common cancer in medium/large and larger breeds with a poor prognosis.
  • increases the risk of cardiac hemangiosarcoma by a factor of 1.6; this is a common cancer and major cause of death in some breeds
  • triples the risk of hypothyroidism
  • increases the risk of geriatric cognitive impairment
  • triples the risk of obesity, a common health problem in dogs with many-associated health problems
  • quadruples the small risk (<0.6%) of prostate cancer
  • doubles the small risk (<1%) of urinary tract cancers
  • increases the risk of orthopedic disorders
  • increases the risk of adverse reactions to vaccinations

For female dogs, the situation is more complex. The number of health benefits associated with spaying may exceed the associated health problems in some (not all) cases. On balance, whether spaying improves odds of overall good health or degrades them probably depends on the age of the female dog and the relative risk of various diseases in the different breeds.

On the positive side, spaying female dogs if done before 2.5 years of age;

  • greatly reduces the risk of mammary tumors, the most common malignant tumors in female dogs
  • nearly eliminates the risk of pyometra, which otherwise would affect about 23% of intact female dogs; pyometra kills about 1% of intact female dogs
  • reduces the risk of perianal fistulas
  •  removes the very small risk (_0.5%) from uterine, cervical, and ovarian tumors

On the negative side, spaying female dogs if done before maturity;

  • increases the risk of osteosarcoma by a factor of 3.1; this is a common cancer in larger breeds with a poor prognosis increases the risk of splenic hemangiosarcoma by a factor of 2.2 and cardiac hemangiosarcoma by a factor of >5; this is a common cancer and major cause of death in some breeds
  • triples the risk of hypothyroidism
  •  increases the risk of obesity by a factor of 1.6-2, a common health problem in dogs with many associated health problems
  • causes urinary “spay incontinence” in 4-20% of female dogs
  • increases the risk of persistent or recurring urinary tract infections by a factor of 3-4
  • inincreases the risk of recessed vulva, vaginal dermatitis, and vaginitis, especially for female dogs spayed before puberty
  • doubles the small risk (<1%) of urinary tract tumors
  • increases the risk of orthopedic disorders
  • increases the risk of adverse reactions to vaccinations

One thing is clear – much of the spay/neuter information that is available to the public is unbalanced and contains claims that are exaggerated or unsupported by evidence. Rather than helping to educate pet owners, much of it has contributed to common misunderstandings about the health risks and benefits associated of spay/neuter in dogs. The traditional spay/neuter age of six months as well as the modern practice of pediatric spay/neuter appear to predispose dogs to health risks that could otherwise be avoided by waiting until the dog is physically mature, or (perhaps in the case of many male dogs) foregoing it altogether unless medically necessary. The balance of long-term health risks and benefits of spay/neuter will vary from one dog to the next. Across-the-board recommendations for all pet dogs do not appear to be supportable from findings in the veterinary medical literature.

FINDINGS FROM STUDIES

This section summarizes the diseases or conditions that have been studied with respect to spay/neuter in dogs.

Complications from Spay/Neuter Surgery All surgery incurs some risk of complications, including adverse reactions to anesthesia, hemorrhage, inflammation, infection, etc. Complications include only immediate and near term impacts that are clearly linked to the surgery, not to longer term impacts that can only be assessed by research studies. At one veterinary teaching hospital where complications were tracked, the rates of intraoperative, postoperative and total complications were 6.3%, 14.1% and 20.6%, respectively as a result of spaying female dogs. Other studies found a rate of total complications from spaying of 17.7%2 and 23%.

A study of Canadian veterinary private practitioners found complication rates of 22% and 19% for spaying female dogs and neutering male dogs, respectively4. Serious complications such as infections, abscesses, rupture of the surgical wound, and chewed out sutures were reported at a 1- 4% frequency, with spay and castration surgeries accounting for 90% and 10% of these complications, respectively. The death rate due to complications from spay/neuter is low, at around 0.1%5.

Prostate Cancer Much of the spay/neuter information available to the public asserts that neutering will reduce or eliminate the risk that male dogs develop prostate cancer. This would not be an unreasonable assumption, given that prostate cancer in humans is linked to testosterone. But the evidence in dogs does not support this claim. In fact, the strongest evidence suggests just the opposite. There have been several conflicting epidemiological studies over the years that found either an increased risk or a decreased risk of prostate cancer in neutered dogs. These studies did not utilize control populations, rendering these results at best difficult to interpret. This may partially explain the conflicting results. More recently, two retrospective studies were conducted that did utilize control populations. One of these studies involved a dog population in Europe6 and the other involved a dog population in America.

Both studies found that neutered male dogs have a four times higher risk of prostate cancer than intact dogs. Based on their results, the researchers suggest a cause-and-effect relationship: “this suggests that castration does not initiate the development of prostates carcinoma in the dog, but does favor tumor progression”6 and also “Our study found that most canine prostate cancers are of ductal/urothelial origin….The relatively low incidence of prostate cancer in intact dogs may suggest that testicular hormones are in fact protective against ductal/urothelial prostatic carcinoma, or may have indirect effects on cancer development by changing the environment in the prostate.”7

This needs to be put in perspective. Unlike the situation in humans, prostate cancer is uncommon in dogs. Given an incidence of prostate cancer in dogs of less than 0.6% from necropsy studies8, it is difficult to see that the risk of prostate cancer should factor heavily into most neutering decisions. There is evidence for an increased risk of prostate cancer in at least one breed (Bouviers)6, though very little data so far to guide us in regards to other breeds.

Testicular Cancer Since the testicles are removed with neutering, castration removes any risk of testicular cancer (assuming the castration is done before cancer develops). This needs to be compared to the risk of testicular cancer in intact dogs. Testicular tumors are not uncommon in older intact dogs, with a reported incidence of 7%9. However, the prognosis for treating testicular tumors is very good owing to a low rate of metastasis10, so testicular cancer is an uncommon cause of death in intact dogs. For example, in a Purdue University breed health survey of Golden Retrievers11, deaths due to testicular cancer were sufficiently infrequent that they did not appear on list of significant causes of “Years of Potential Life Lost for Veterinary Confirmed Cause of Death” even though 40% of GR males were intact. Furthermore, the GRs who were treated for testicular tumors had a 90.9% cure rate. This agrees well with other work that found 6-14% rates of metastasis for testicular tumors in dogs12. The high cure rate of testicular tumors combined with their frequency suggests that fewer than 1% of intact male dogs will die of testicular cancer. In summary, though it may be the most common reason why many advocate neutering young male dogs, the risk from life threatening testicular cancer is sufficiently low that neutering most male dogs to prevent it is difficult to justify. An exception might be bilateral or unilateral cryptorchids, as testicles that are retained in the abdomen are 13.6 times more likely to develop tumors than descended testicles13 and it is also more difficult to detect retained tumors by routine physical examination.

Osteosarcoma (Bone Cancer) a multi-breed case-control study of the risk factors for osteosarcoma found that spay/neutered dogs (males or females) had twice the risk of developing osteosarcoma, as did intact dogs14. This risk was further studied in Rottweilers, a breed with a relatively high risk of osteosarcoma. This retrospective cohort study broke the risk down by age at spay/neuter, and found that the elevated risk of osteosarcoma is associated with spay/neuter of young dogs15. Rottweilers spayed/neutered before one year of age were 3.8 (males) or 3.1 (females) times more likely to develop osteosarcoma than intact dogs. Indeed, the combination of breed risk and early spay/neuter meant that Rottweilers spayed/neutered before one year of age had a 28.4% (males) and 25.1% (females) risk of developing osteosarcoma. These results are consistent with the earlier multi-breed study14 but have an advantage of assessing risk as a function of age at neuter.

The researchers suggest a cause-and-effect relationship, as sex hormones are known to influence the maintenance of skeletal structure and mass, and also because their findings showed an inverse relationship between time of exposure to sex hormones and risk of osteosarcoma.15 The risk of osteosarcoma increases with increasing breed size and especially height14. It is a common cause of death in medium/large, large, and giant breeds. Osteosarcoma is the third most common cause of death in Golden Retrievers11 and is even more common in larger breeds14. Given the poor prognosis of osteosarcoma and its frequency in many breeds, spay/neuter of immature dogs in the medium/large, large, and giant breeds is apparently associated with a significant and elevated risk of death due to osteosarcoma.

Mammary Cancer (Breast Cancer) Mammary tumors are by far the most common tumors in intact female dogs, constituting some 53% of all malignant tumors in female dogs in a study of dogs in Norway16 where spaying is much less common than in the USA. 50-60% of mammary tumors are malignant, for which there is a significant risk of metastasis17. Mammary tumors in dogs have been found to have estrogen receptors18, and the published research19 shows that the relative risk (odds ratio) that a female will develop mammary cancer compared to the risk in intact females is dependent on how many estrus cycles she experiences: # of estrus cycles before spay Odds Ratio None 0.005 1 0.08 2 or more 0.26 Intact 1.00 The same data when categorized differently showed that the relative risk (odds ratio) that females will develop mammary cancer compared to the risk in intact females is indicated that: Age at Spaying Odds Ratio _ 29 months 0.06 _ 30 months 0.40 (not statistically significant at the P<0.05 level) Intact 1.00

Please note that these are RELATIVE risks. This study has been referenced elsewhere many times but the results have often been misrepresented as absolute risks. A similar reduction in breast cancer risk was found for women under the age of 40 who lost their estrogen production due to “artificial menopause”20 and breast cancer in humans is known to be estrogen activated. Mammary cancer was found to be the 10th most common cause of years of lost life in Golden Retrievers, even though 86% of female GRs were spayed, at a median age of 3.4 yrs11. Considering that the female subset accounts for almost all mammary cancer cases, it probably would rank at about the 5th most common cause of years of lost life in female GRs. It would rank higher still if more female GRs had been kept intact up to 30 months of age. Boxers, cocker spaniels, English springer spaniels, and dachshunds are breeds at high risk of mammary tumors16. A population of mostly intact female Boxers was found to have a 40% chance of developing mammary cancer between the ages of 6-12 years of age16. There are some indications that purebred dogs may be at higher risk than mixed breed dogs, and purebred dogs with high inbreeding coefficients may be at higher risk than those with low inbreeding coefficients21. More investigation is required to determine if these are significant. In summary, spaying female dogs significantly reduces the risk of mammary cancer (a common cancer), and the fewer estrus cycles experienced at least up to 30 months of age, the lower the risk will be.

Female Reproductive Tract Cancer (Uterine, Cervical, and Ovarian Cancers) Uterine/cervical tumors are rare in dogs, constituting just 0.3% of tumors in dogs22. Spaying will remove the risk of ovarian tumors, but the risk is only 0.5%23. While spaying will remove the risk of reproductive tract tumors, it is unlikely that surgery can be justified to prevent the risks of uterine, cervical, and ovarian cancers as the risks are so low.

Urinary Tract Cancer (Bladder and Urethra Cancers) An age-matched retrospective study found that spay/neuter dogs were two times more likely to develop lower urinary tract tumors (bladder or urethra) compared to intact dogs24. These tumors are nearly always malignant, but are infrequent, accounting for less than 1% of canine tumors. So this risk is unlikely to weigh heavily on spay/neuter decisions. Airedales, Beagles, and Scottish Terriers are at elevated risk for urinary tract cancer while German Shepherds have a lower than average risk24.

Hemangiosarcoma Hemangiosarcoma is a common cancer in dogs. It is a major cause of death in some breeds, such as Salukis, French Bulldogs, Irish Water Spaniels, Flat Coated Retrievers, Golden Retrievers, Boxers, Afghan Hounds, English Setters, Scottish Terriesr, Boston Terriers, Bulldogs, and German Shepherd Dogs25. In an aged-matched case controlled study, spayed females were found to have a 2.2 times higher risk of splenic hemangiosarcoma compared to intact females25. A retrospective study of cardiac hemangiosarcoma risk factors found a >5 times greater risk in spayed female dogs compared to intact female dogs and a 1.6 times higher risk in neutered male dogs compared to intact male dogs.26 The authors suggest a protective effect of sex hormones against hemangiosarcoma, especially in females. In breeds where hermangiosarcoma is an important cause of death, the increased risk associated with spay/neuter is likely one that should factor into decisions on whether or when to sterilize a dog.

Hypothyroidism Spay/neuter in dogs was found to be correlated with a three fold increased risk of hypothyroidism compared to intact dogs. The researchers suggest a cause-and-effect relationship27. They wrote: “More important [than the mild direct impact on thyroid function] in the association between [spaying and] neutering and hypothyroidism may be the effect of sex hormones on the immune system. Castration increases the severity of autoimmune thyroiditis in mice” which may explain the link between spay/neuter and hypothyroidism in dogs. Hypothyroidism in dogs causes obesity, lethargy, hair loss, and reproductive abnormalities.28

Obesity Owing to changes in metabolism, spay/neuter dogs are more likely to be overweight or obese than intact dogs. One study found a two fold increased risk of obesity in spayed females compared to intact females29. Another study found that spay/neuter dogs were 1.6 (females) or 3.0 (males) times more likely to be obese than intact dogs, and 1.2 (females) or 1.5 (males) times more likely to be overweight than intact dogs30. A survey study of veterinary practices in the UK found that 21% of dogs were obese.29 Being obese and/or overweight is associated with a host of health problems in dogs. Overweight dogs are more likely to be diagnosed with hyperadrenocorticism, ruptured cruciate ligament, hypothyroidism, lower urinary tract disease, and oral disease31. Obese dogs are more likely to be diagnosed with hypothyroidism, diabetes mellitus, pancreatitis, ruptured cruciate ligament, and neoplasia (tumors) 31.

Diabetes Some data indicate that neutering doubles the risk of diabetes in male dogs, but other data showed no significant change in diabetes risk with neutering32. In the same studies, no association was found between spaying and the risk of diabetes.

Adverse Vaccine Reactions A retrospective cohort study of adverse vaccine reactions in dogs was conducted, which included allergic reactions, hives, anaphylaxis, cardiac arrest, cardiovascular shock, and sudden death. Adverse reactions were 30% more likely in spayed females than intact females, and 27% more likely in neutered males than intact males33. The investigators discuss possible cause-and-effect mechanisms for this finding, including the roles that sex hormones play in body’s ability to mount an immune response to vaccination.33 Toy breeds and smaller breeds are at elevated risk of adverse vaccine reactions, as are Boxers, English Bulldogs, Lhasa Apsos, Weimaraners, American Eskimo Dogs, Golden Retrievers, Basset Hounds, Welsh Corgis, Siberian Huskies, Great Danes, Labrador Retrievers, Doberman Pinschers, American Pit Bull Terriers, and Akitas.33 Mixed breed dogs were found to be at lower risk, and the authors suggest genetic hetereogeneity (hybrid vigor) as the cause.

Urogenital Disorders Urinary incontinence is common in spayed female dogs, which can occur soon after spay surgery or after a delay of up to several years. The incidence rate in various studies is 4-20% 34,35,36 for spayed females compared to only 0.3% in intact females37. Urinary incontinence is so strongly linked to spaying that it is commonly called “spay incontinence” and is caused by urethral sphincter incompetence38, though the biological mechanism is unknown. Most (but not all) cases of urinary incontinence respond to medical treatment, and in many cases this treatment needs to be continued for the duration of the dog’s life.39 A retrospective study found that persistent or recurring urinary tract (bladder) infections (UTIs) were 3-4 times more likely in spayed females dogs than in intact females40. Another retrospective study found that female dogs spayed before 5 ½ months of age were 2.76 times more likely to develop UTIs compared to those spayed after 5 ½ months of age.41 Depending on the age of surgery, spaying causes abnormal development of the external genitalia. Spayed females were found to have an increased risk of recessed vulva, vaginal dermatitis, vaginitis, and UTIs.42 The risk is higher still for female dogs spayed before puberty.42

Pyometra (Infection of the Uterus) Pet insurance data in Sweden (where spaying is very uncommon) found that 23% of all female dogs developed pyometra before 10 years of age43. Bernese Mountain dogs, Rottweilers, rough-haired Collies, Cavalier King Charles Spaniels and Golden Retrievers were found to be high-risk breeds43. Female dogs that have not whelped puppies are at elevated risk for pyometra44. Rarely, spayed female dogs can develop “stump pyrometer” related to incomplete removal of the uterus. Pyometra can usually be treated surgically or medically, but 4% of pyometra cases led to death43. Combined with the incidence of pyometra, this suggests that about 1% of intact female dogs will die from pyometra.

Perianal Fistulas Male dogs are twice as likely to develop perianal fistulas as females, and spay/neutered dogs have a decreased risk compared to intact dogs45. German Shepherd Dogs and Irish Setters are more likely to develop perianal fistulas than are other breeds.45

Non-cancerous Disorders of the Prostate Gland The incidence of benign prostatic hypertrophy (BPH, enlarged prostate) increases with age in intact male dogs, and occurs in more than 80% of intact male dogs older than the age of 5 years. Most cases of BPH cause no problems, but in some cases the dog will have difficulty defecating or urinating. Neutering will prevent BPH. If neutering is done after the prostate has become enlarged, the enlarged prostate will shrink relatively quickly. BPH is linked to other problems of the prostate gland, including infections, abscesses, and cysts, which can sometimes have serious consequences.

Orthopedic Disorders In a study of beagles, surgical removal of the ovaries (as happens in spaying) caused an increase in the rate of remodeling of the ilium (pelvic bone)47, suggesting an increased risk of hip dysplasia with spaying. Spaying was also found to cause a net loss of bone mass in the spine 48. Spay/neuter of immature dogs delays the closure of the growth plates in bones that are still growing, causing those bones to end up significantly longer than in intact dogs or those spay/neutered after maturity. Since the growth plates in various bones close at different times, spay/neuter that is done after some growth plates have closed but before other growth plates have closed can result in a dog with unnatural proportions, possibly impacting performance and long term durability of the joints. Spay/neuter is associated with a two fold increased risk of cranial cruciate ligament rupture50. Perhaps this is associated with the increased risk of obesity29 or to changes in body proportions in dogs spay/neutered before the growth plates in the bones have closed49. Spay/neuter before 5 ½ months of age is associated with a 70% increased aged-adjusted risk of hip dysplasia compared to dogs spayed/neutered after 5 ½ months of age41. The researchers suggest “it is possible that the increase in bone length that results from early-age gonadectomy results in changes in joint conformation, which could lead to a diagnosis of hip dysplasia”. In a breed health survey study of Airedales, spay/neuter dogs were significantly more likely to suffer hip dysplasia as well as “any musculoskeletal disorder”, compared to intact dogs51, however possible confounding factors were not controlled for, such as the possibility that some dogs might have been spayed/neutered because they had hip dysplasia or other musculoskeletal disorders. Compared to intact dogs, another study found that dogs neutered six months prior to a diagnosis of hip dysplasia were 1.5 times as likely to develop clinical hip dysplasia.

Geriatric Cognitive Impairment Neutered male dogs and spayed female dogs are at increased risk of geriatric cognitive impairment compared to intact male dogs53. There weren’t enough intact geriatric females available for the study to determine their risk. Geriatric cognitive impairment includes disorientation in the house or outdoors, changes in social interactions with human family members, loss of house training, and changes in the sleep-wake cycle53. The investigators state “This finding is in line with current research on the neuro-protective roles of testosterone and estrogen at the cellular level and the role of estrogen in preventing Alzheimer’s disease in human females. One would predict that estrogens would have a similar protective role in the sexually intact female dogs; unfortunately too few sexually intact female dogs were available for inclusion in the present study to test the hypothesis”

CONCLUSIONS

An objective reading of the veterinary medical literature reveals a complex situation with respect to the longterm health risks and benefits associated with spay/neuter in dogs. The evidence shows that spay/neuter correlates with both positive AND adverse health effects in dogs. It also suggests how much we really do not yet understand about this subject. On balance, it appears that no compelling case can be made for neutering most male dogs to prevent future health problems, especially immature male dogs. The number of health problems associated with neutering may exceed the associated health benefits in most cases. For female dogs, the situation is more complex. The number of health benefits associated with spaying may exceed the associated health problems in many (not all) cases. On balance, whether spaying improves the odds of overall good health or degrades them probably depends on the age of the dog and the relative risk of various diseases in the different breeds. The traditional spay/neuter age of six months as well as the modern practice of pediatric spay/neuter appear to predispose dogs to health risks that could otherwise be avoided by waiting until the dog is physically mature, or (perhaps in the case of many male dogs) foregoing it altogether unless medically necessary. The balance of long-term health risks and benefits of spay/neuter will vary from one dog to the next. Across-the-board recommendations for all dogs do not appear to be supportable from findings in the veterinary medical literature.