A couple of years ago, I wrote a review of the risks and benefits of neutering. This handout, originally intended for clients, was also turned into a journal article for veterinarians:
Evaluating the benefits and risks of neutering dogs and cats CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources 2010 5, No. 045
This was a narrative review, not a systematic review. This means that I found as many research reports as possible related to the subject and informally evaluated their conclusions. I did not conduct a formal appraisal of the level and quality of the research evidence according to predetermined and standardized criteria, as would be done in a systematic review.
There are pros and cons to each format. A narrative review is more likely to reach pragmatic conclusions based on the existing evidence, whereas a systematic review is more likely to end with no useful conclusion if the quality of the evidence examined is less that perfect, which it almost always is. However, a systematic review is likely to be more thorough and provides a better picture of how strong the existing evidence is so that it is possible to gauge how much confidence we ought to have in the conclusions we base on it.
As a practicing clinician, I need to make practical decisions even when the evidence isn’t perfect, so a narrative review was more suited to my goals. However, as a strong supporter of the practice of evidence-based veterinary medicine, I believe systematic reviews and a clear understanding of the limitations of the available evidence on specific subjects is critical to making fully informed decisions. So I am thrilled to see that a research group in the U.K. has begun producing a series of systematic reviews of the evidence concerning the risks and benefits of neutering in dogs. I intend to evaluate these reviews as they appear to help update and appraise the evidence on this important subject and provide a bit of context for veterinarians and pet owners trying to make practical decisions about neutering. The first subject reviewed was the potential effect of neutering on the risk of urinary incontinence.
Beauvais W, Cardwell JM, Brodbelt DC.The effect of neutering on the risk of urinary incontinence in bitches – a systematic review.J Small Anim Pract. 2012 Apr;53(4):198-204.
In my 2010 narrative review, I was only able to report research suggesting urinary incontinence was common in spayed female dogs and that the research was conflicting on whether incontinence was more common in dogs spayed at younger ages. I did not identify specific research comparing the occurrence of incontinence in intact and spayed females.
The UK group identified only one research study evaluating the relative risk of incontinence in neutered and intact dogs, and three studies evaluating the effect of age at neutering on incontinence risk. The authors concluded the following:
1. All the evidence was weak, with a significant risk of error
2. The one study that evaluated risk of incontinence with neutering found that neutering significantly increased the risk of incontinence.
3. Two of the three studies found no association between age at neutering and incontinence and one found that incontinence was more likely the younger dogs were when neutered.
So the conclusions are consistent with the current consensus, that neutering female dogs does increase the risk of urinary incontinence and that age at neutering probably does not affect this risk significantly. There is, of course, significant uncertainty because the evidence is quite weak. That does not mean, however, we cannot reach a conclusion or make recommendations. If this were the case, we would almost never be able to decide anything in medicine since the evidence is often imperfect. It simply means that we have to acknowledge the uncertainty and recognize that our conclusions are provisional and might need to change as new evidence emerges.
Any decision about neutering should not, of course, be based solely on this single issue. Urinary incontinence, while inconvenient, is a relatively minor and highly treatable clinical problem. And there are a large number of other risks, benefits, and personal considerations involved in making a decision about neutering. The important thing is that we make informed decisions and that we understand the strengths and weaknesses in the available evidence. The reviews produced by this group will be invaluable in facilitating this.