How old does a male dog have to be to breed with a female? The answer is…younger than you'd think! Surprisingly, these Pug mix puppies were born after Priscilla mated with a 6 month old Chihuahua. Labor and delivery were very hard on her, but Dr. Lindsey brought her through it all with IV fluids, medications, and an emergency spay surgery. We recommend spaying or neutering pets at 4-6 months of age, or shortly after they finish their series of puppy or kitten vaccines.