You have opened a real can of worms with your question! Because spay and neuter has been so common in this country (i.e., the US) very little attention has been paid to the non-reproductive effects of male and female hormones. Further complicating matters, there was little information in that subject across the board until relatively recently. What few articles appeared about any negative effects in dogs were often published in journals to which few had access. However that has started to change and if you go to http://www.mmilani.com/spay-neuter-references.html you’ll find a list of articles that cover a wide range of topics related to this issue. I try to update it as time allows, but time doesn’t always allow! :-)
Most of the benefits currently being explored are associated with allowing a dog to become sexually mature rather than breeding the animal. Relative to any benefits associated with breeding itself, I’m not aware of any studies that compare this population to those who were spayed or neutered pre-maturely or maturely. Such studies would also need to compare those who had been bred only 1-2 times vs. those who had a normal reproductive life. But even finding dogs who have a normal reproductive life poses a problem because dogs’ reproductive lives are often orchestrated by humans rather than Mother Nature.
Aside from that, when I work up my behavior cases I always ask my clients if their animals display any sexual behaviors. I can say with certainty that lack of testicles or ovaries will not prevent these in some animals any more than their presence will guarantee mating success in others.
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