Dogs that undergo the spaying process usually stop menstruating, but there are cases where a dog appears to be in heat following surgery, which usually means that the surgery did not completely remove all necessary reproductive tissue. After tests to confirm that a female dog still has some reproductive tissue, a veterinarian can perform a secondary surgery to remove the remaining tissue.
Spaying a dog has benefits beyond eliminating menstruation. Spayed dogs have greater protection against uterine and ovarian cancers and reproductive infections. Spaying also reduces the risk of a dog running away to find a mate or being attacked by overly aggressive male dogs during the menstrual cycle.