Many breeders and veterinarians in North America promote the neutering of dogs claiming various health benefits, with an estimated 83% of all dogs in the United States being indeed castrated or spayed. This is in a marked contrast with European countries where neutering is typically avoided and not promoted by animal health authorities or professionals, or even countries like Norway where the practice is outright banned.
This common North American practice of neutering animals, and specifically male dogs, has no ground in science, and appears to be solely based on societal trends stigmatizing any natural behavior or characteristics associated with males and testosterone. As a matter of fact, scientific research establishes a clear link, and even causation, between neutering male dogs and a long list of serious and life threatening health ailments.
In a study by the American Association of Cancer Research (Endogenous Gonadal Hormone Exposure and Bone Sarcoma Risk), neutered dogs were much more likely to develop osteosarcoma (a deadly form of bone cancer) than those left sexually intact.
In another study published by PLOS Genetics (Neutering Dogs: Effects on Joint Disorders and Cancers in Golden Retrievers), neutered dogs had a higher incidence of hip dysplasia, cruciate ligament disease, lymphosarcoma, hemangiosarcoma, and mast cell tumors compared to intact males.
Even prostate cancer has been found to be 4 times more prevalent in castrated dogs compared to intact animals in a 2007 study (A population study of neutering status as a risk factor for canine prostate cancer) presented at the 25th Annual Conference of the Veterinary Cancer Society.
Overall, scientific research clearly establishes that sex hormones, including testosterone, are protective against many forms of cancer in dogs, thereby offsetting any alleged (and either largely unproven or subjective) minor health benefits associated with castration.