Cats: why the five-month target?
Cats can become reproductively active surprisingly young. FelineVMA/AAFP-supported initiatives recommend sterilization by five months for cats not intended for breeding, helping prevent unplanned litters before the first heat in many females.
Small and large dogs are not identical
AAHA life-stage guidance has historically supported earlier neutering for many small dogs while allowing later timing for larger dogs after more skeletal growth. Breed-specific observational studies have found different associations between age at neutering and some orthopedic or cancer outcomes.
What the evidence cannot do
Most timing studies are observational and cannot prove that one age directly causes or prevents a later disorder in every dog. Breed, genetics, body condition, activity, and healthcare also influence outcomes.
Questions to discuss with your veterinarian
What is the expected adult weight? Can intact males and females be reliably separated? Are there breed-specific orthopedic concerns? Is there a medical reason to operate sooner? For females, how do pregnancy prevention, pyometra risk, mammary-tumor considerations, and potential urinary effects fit the individual case?