Any causal attribution for neutering and problematic behavior is premature, although I have not touched on hormones and brain
aging—an even more complex issue. Frankly, behavioral studies are much harder to do than studies focusing purely on somatic
conditions. When one considers the difficulty of identifying physical pathologies that may be affected by neutering, one should
take special care with behavioral evaluations, which are much more difficult to evaluate in an unbiased, valid and repeatable
So what do I recommend to owners seeking guidance? If the dog has any pathology that might be heritable—behavioral or otherwise—the
dog should not be bred unless the breeding is part of a funded, approved, controlled study in collaboration with researchers
to study the putative defect. Neutering is not the only way of preventing breeding but it is the easiest.
If the dog has no behavioral concerns and the owners are responsible, discuss all of the health information outlined above.
While the Hopkins study has never been replicated or expanded, I still note to clients that dogs that are searching for mates
are a lot like college students in bars: They are not typically thinking about the consequences of their behavioral choices.
Too often these dogs roam and are killed by cars. Clients keeping intact males must be mindful of keeping them safe.
In summary, we need to learn more about patterns of all pathologies in all breeds so we can help produce physically and behaviorally
healthier animals that are excellent at their jobs—whether they're bred to be excellent pets or to be service, working, trial
or hunting dogs—and that will always have caring, humane homes.
One study has suggested that neutered dogs are more fearful, excitable, aggressive and less trainable than are intact dogs.36 Unfortunately, this study is flawed in that it does not follow dogs through time and instead relies on unmatched cohorts.
We do not know whether these dogs were all evaluated at the same age (a control for ontogeny) or at a predetermined time after
neutering (a control for postoperative effects). Without these controls, most correlations—especially using scored and ranked
data, as is the case here—are likely to be spurious. There are other major methodological issues that preclude accepting these
conclusions as valid and they are common enough mistakes in studies to warrant an outline here.
> The data are scored clients' assessments of their dog's behaviors using a scale that was not validated to ensure it represented
reliable, repeatable behaviors (e.g., whether the dog was actually "aggressive" if she barked).
> No inter-rater reliability data are provided. In other words, we have no idea how variable clients' interpretations of the
dogs' behaviors were or how variable their interpretation of the terms and scales were.
> Scaled data are difficult to interpret because they are so subjective and without inter- and intra-rater reliabilities, it
is impossible to know, for example, if person A's 4.5 is equivalent to person B's 4.5. This is one reason why such scales
should be avoided in population studies unless they are defined, validated and tested for inter-rater agreement (e.g., Kappa scores)..
> The data are presented graphically and the axes are not the same. As a result, differences appear larger than they truly
are. When plotted on the same scale, differences are modest, especially given that very small changes in scores obtained from
scaled responses are calculated for a very large number of responses.
> The sample size is huge, because this is a survey study, and with a sample size so large it would be odd if some findings
were not significant, by chance alone. This effect is magnified when scores are calculated from scales. Even for those relationships
that are statistically different, we have no idea if the differences noted are biologically meaningful.
> Analysis of ratios is complex (in this case, bone length), and requires certain assumptions which we cannot know were met
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Dr. Karen L. Overall is a researcher, editor of The Journal of Veterinary Behavior: Clinical Applications and Research, and author of more than 100 publications, dozens of chapters and a new book, The Manual of Clinical Behavioral Medicine for Dogs and Cats.