Spaying and neutering companion animals prevents population overpopulation and provides individual health benefits, though optimal timing is increasingly nuanced.
Spay-neuter programs address welfare at both population and individual levels. Population-level benefits include reducing the millions of animals entering shelters and facing euthanasia. Individual health benefits include elimination of reproductive cancers and diseases, reduced roaming that prevents road injuries, and reduced aggression in some animals. Emerging research on optimal timing in large breed dogs introduces nuance, but the welfare case for spay-neuter in community cat and dog populations remains overwhelming.