Spaying or neutering a pet is an important preventive health measure as well as a means of limiting the number of homeless pets, writes veterinarian Ann Hohenhaus, who notes that the American Veterinary Medical Association's Guidelines for Responsible Pet Ownership encourage owners to help keep the pet population under control. During a neuter operation, a veterinarian removes a male dog's testicles, the main source of testosterone. This prevents the dog from siring puppies and protects it from testosterone-related problems including behavior issues and health threats such as prostate cancer, Hohenhaus points out.