As part of my ongoing surveillance of evidence concerning the benefits and risks of neutering, I have identified a new study on the subject.
Hart, B. L., Hart, L. A., Thigpen, A. P. and Willits, N. H. (2016). Neutering of German Shepherd Dogs: associated joint disorders, cancers and urinary incontinence. Veterinary Medicine and Scienc. doi: 10.1002/vms3.34
This study is a retrospective that looks through the records of the veterinary hospital at the University of California at Davis. It is a product of the same research group that has produced several other similar studies I have also reviewed. These earlier studies found some interesting differences between even closely related breeds, such as Labrador retrievers and golden retrievers, which suggests that generalizations applicable to all dogs regardless of breed are unlikely to be very reliable. This is always frustrating, since simply, universal rules are more appealing and easier to apply than nuanced, complicated risk/benefit calculations, but science often shows us that nature is more complex than we might wish. This study illustrates again the importance of breed in evaluating the potential effects of neutering.
This study includes some of the same limitations I have discussed when evaluating previous studies by this group. For example, except when evaluating mammary cancer, the authors did not consider diagnoses in dogs over eight years of age. Their rationale is that the effects of neutering might be swamped by other factors in older dogs, making them harder to detect. While this may be true, it is an assumption that has not been demonstrated to actually be true. And since overall health and disease occurrence, mortality, and longevity are the outcomes of real interest to pet owners, not just diseases that occur in the first eight years of life, using a cutoff like this can misrepresent the real importance of neutering. If, as some evidence suggests, neutered animals live longer overall than intact animals, for example, then neutering might still be the better choice even if one can show it causes more of some types of disease in the first eight years of life.
And a I have discussed in the context of their previous papers, and the authors themselves acknowledge, this study uses records pertaining to dogs seen at a university veterinary hospital. The people and patients who go to vet schools for treatment differ in a number of ways from those who don’t, and these differences may effect the diseases they get and the impact of neutering on health. This doesn’t invalidate the data or conclusions, of course, but it means we must be cautious in extrapolating these to first opinion practice populations.
The authors evaluated the impact of neutering before 6 months of age, between 6 and 11 months of age, between 1 and 2 years of age, and between 2 and 8 years of age on the occurrence of various disease compared with un-neutered dogs. Here is a brief summary of the findings:
- Neutering before 12 months of age (combining the < 6 months group and the 6-12 months group) was associated with a higher risk of cranial cruciate ligament ruptures in both neutered males and females compared with intact dogs. This is similar to the findings for golden retrievers, though no increase in risk was found for Labrador retrievers except in males neutered before 6 months of age.
- Neutering, regardless of age, was not associated with any difference in the risk of hip dysplasia or elbow dysplasia. In contrast, similar earlier studies did find an increase in hip dysplasia risk in male golden retrievers neutered before 12 months of age and an increase in risk for female Labrador retrievers neutered before 2 years, but no increase for female goldens or male labs. As always the devil is in the details.
- Neutering, regardless of age, was not associated with any increase in risk of any cancer. Some earlier studies have found inconsistent and complicated increases in the risk of some cancers that vary with age at neutering, sex, and breed. Broad generalizations about neutering and cancer risk seem difficult to support given this variability in the data.
- No statistically significant difference was found between neutered and intact females in the risk of mammary cancer. However, very few cases were found (only 14 out of 450 dogs), possibly due to the cutoff of 11 years of age used.
- Urinary incontinence was significantly more common in females neutered between 6 and 11 months of age than intact females. Differences for other neutering ages and intact females were not significant, but there were no cases of incontinence in intact females.
- All cases of pyometra were in intact females, of course. This only occurred in about 2.5% of the females, However, since this disease becomes more common with age and the dogs were only evaluated up to 8 years of age, this likely under-represents the real risk of this problem in intact females.
Overall, this study adds yet another small but useful bit of information for vets and dog owners to consider in making decisions about neutering. It emphasizes yet again that the impact of neutering differs significantly between breeds, and general rules cannot be reliably applied to all dogs.
Thank you so much for staying on top of these studies! Having adopted a Saint Bernard who was neutered at the age of (probably) two-ish, I’m hopeful that we’ll see some fresh info covering giant breeds sometime fairly soon.
Adding my thanks too. We neutered our female GSD when we got her at about five months from a rescue (art of their contract)and I regreted it because I think her behaviour would have improved more quickly if she had been intact. She’d been kept in a shed up to the point she was handed in to the rescue and was frightened of everything, even grass. It’s so difficult to be sure on behavioural things. On the other hand I can be sure she snapped her left cruciate ligament, she has recovered brilliantly, but obviously not something one would put them through if there is a simle way to reduce the risk.
Is there a typo in the bullet point on mammary cancer, it talks of risk until 11 years whereas in the text you say they don’t go beyond 8 years?
They actually used the 8 years of age cutoff for everything except mammary cancer, which they chose to count up to 11. I’m not convinced by their rationale for why this made sense.
Oh ho these studies are so confusing. Thanks for reviewing them.
I still find myself scratching my head. The social scientist in me wants to use a risk:benefit framework. This means the question is not only whether neutering raises or lowers the risk of a disease or condition. It’s critical to know ‘by how much’ … and also important to have a metric for the risks or benefits. How do you weigh a 10% increase in risk of breast cancer against a 10% decrease in risk of HD (or whatever). Also, I suspect the risks for bitches are affected by their breeding history. For humans, childbearing history seems to be an important term in the equation.
The statistician in me questions how you find a representative sample for a breed. Anecdotal evidence (ie., breeders’ scuttlebutt) says diseases run strong in some bloodlines within a breed but are rare in other bloodlines. Stats from one university vet practice fit in the category of ‘convenience sampling’ . . . which statisticians don’t much like because it often imparts strong biases. Seems to me quite likely that, say, the Labradors (or any other breed) around UC Davis (or any other vet school) will tend to over-represent some bloodlines and under-represent others. All these apparent breed differences may in fact be artefacts of biased sample selection.
All in all, I haven’t read anything on this that convinces me that the health risks/benefits of spay/neutering are strong enough to be a deciding factor, apart from exceptional cases where there is a strong reason to desex. All in all, I see no strong argument to vary from my normal pattern (for dogs): desex when fully mature except where you want to breed the dog.
In the end, I think the highest benefit of such studies is in raising questions about the knee jerk reaction to desex them all, and to encourage people and veterinarians to think about desexing in terms of lifestyle and reproductive choices.
That is a good point about blood lines and the likely effect on the sample used. I get rescues – there are a lot of people who discover they can not handle a teenage GSD and my home set up permits me to take quite difficult dogs – so I’m unlikely to know the dogs blood line.
Absolutely. There will never be perfect evidence, but we need to make decisions, and the best we can do is make them on the basis of the best evidence we have. The increasing awareness of the complexity of this issue is leading to more research, and little by little patterns are emerging. The importance of breed is one of those patterns. The relationship between neutering and cruciate ligament disease is another. Over time, hopefully, we will be able to make more rational and nuanced choices about neutering as the evidence improves.
Spay neuter updates on 30 breeds of dogs plus 5 weight classes of mixed breeds, as well as international and humane society challenges. At ISAZ satellite symposium, UC Davis June 26. Webinar in realtime also available.