The timing and decision to spay or neuter dogs involves welfare trade-offs between population control benefits and individual health risks.
The welfare calculus around spaying and neutering is more complex than commonly presented. Traditional recommendations for early spay-neuter at 6 months reflect population control priorities and were established before robust long-term health outcome data existed. Newer research indicates that gonadal hormones play important roles in musculoskeletal and immune system development, and that early removal in some breeds increases the risk of certain conditions including joint disorders, urinary incontinence in females, and some cancers. This does not mean spay-neuter is harmful overall — the benefits for population control and some individual health outcomes remain significant. It does mean the decision should be made in consultation with a vet, with consideration of individual breed, sex, lifestyle, and risk profile.