The best age to spay a female dog depends on the breed and size of the dog. According to the AAHA Canine Life Stage Guidelines, small-breed dogs (under 45 pounds projected adult body weight) should be spayed at six months of age. However, recent studies suggest that the best age to spay or neuter should be tailored to each individual dog, especially if the dog is a large or giant breed. For most female dogs, spaying should happen around 9-10 months of age or older. Small dogs do not have as many orthopedic issues, so it is fine to spay them on the younger side at 6-12 months of age. For large dogs that are very prone to orthopedic injury/diseases, it is recommended to wait to spay until 9-18 months of age. Waiting until a female dog is closer to maturity can result in lower risk of orthopedic issues, a reduced risk of cancers (especially breast cancer), and a reduced risk of urinary incontinence. It is important to discuss the best age to spay your female dog with your veterinarian, who can help you identify any potential medical concerns in the future that could be impacted by an early spay.