Spay / neuter

What the surgery changes

• Eliminates risk of pyometra (life-threatening uterine infection in intact females).
• Eliminates testicular cancer and substantially reduces prostate disease in males.
• Reduces, but does not eliminate, mammary cancer risk in females, with the magnitude depending strongly on age at spay.
• Reduces roaming, marking, and intermale aggression in many dogs; effects in cats are more consistent.
• Removes seasonal estrus cycles in females; eliminates unintended litters.

Timing, the conversation has changed

The historical default of spay/neuter at 6 months is no longer supported as a universal recommendation. For large- and giant-breed dogs, growth-plate closure depends on sex hormones; early sterilization (before ~12–18 months depending on breed) is associated with increased risk of cranial cruciate ligament rupture, hip dysplasia, and certain cancers (osteosarcoma, hemangiosarcoma, lymphoma) in some breeds.

Current AAHA guidance is breed- and size-specific. Small dogs and cats are typically sterilized at or before 6 months. Large- and giant-breed dogs are increasingly delayed until skeletal maturity. The right decision is breed-specific and should be made with your vet, weighing the population-level cancer risks against the immediate risks of intact reproductive life.

Alternatives to traditional sterilization

Ovariectomy (removing ovaries only, leaving the uterus) is increasingly used in females, shorter surgery, equivalent disease prevention. Vasectomy and ovary-sparing spay leave hormones intact while preventing reproduction; they are uncommon in the US but available, and may be appropriate for owners who want fertility control without hormonal loss.

Why it matters

The 'always spay at 6 months' default served population-level shelter relinquishment well but produced real individual orthopedic and oncologic costs in large breeds. The right answer is no longer one age, it is a per-animal conversation that weighs cancer risk, joint health, and behavior.