A: We recommend that this procedure be performed at 5-6 months of age. The puppy/kitten is finished with his initial vaccination series, has a little more weight and a better ability to handle the physical stress of surgery. Also, any retained baby teeth can be extracted and the pet will not have to endure a separate anesthetic procedure. For spays, performing the surgery before the first heat cycle (age 6 months) dramatically decreases the risk of breast cancer to 0.5%.