Typically, the animal is best if spayed by the age of 4 months, because both dogs and cats enter their first heat at 4 to 6 months old. If your pet appears to go into heat after the surgery, contact your vet. Most likely some ovarian tissue was left intact during surgery and that tissue releases hormones that can cause the animal to go into heat.
Learn more about the female dog and cat anatomy and the surgical spaying procedure to understand how a pet might be in heat after a surgery. Find out the potential causes for concern over unwanted pet pregnancy and heat cycles.
Dog and Cat Uterus and Ovaries
In dogs and cats, the uterus is shaped like a long "Y." The body of the uterus is the stem of the Y, which is short relative to the long arms called the horns. The horns are where the puppies and kittens are formed, attached, and grow during gestation.
The ovaries, while separate from the uterus, are attached by way of ligaments and blood vessels to both the uterine horns and body. The veterinarian must separate the ovaries from the attachments in the body by clamping and tying off the blood vessels.
Each ovary is in a sac. The sac is often filled with fat—more so in older or overweight animals. Sometimes, the ovarian tissue is diffuse, sometimes it is small or not well formed at the time of the spay. It may also be ectopic, meaning it isn't where it should be in the body, which is a congenital problem.
What Happens During Surgery
The uterus is removed at the base of the Y. The cervix remains in the body.
Sometimes, when the veterinarian clamps the tissue to ligate (or tie off) the blood vessels, small bits of ovarian tissue remain in the body after the surgery. This tissue can then grow and respond to chemical signals from the brain to produce the hormones that cause the heat cycle.
How then can the pet actually bleed if the uterus and ovaries have been removed? The lining tissue of the remaining vagina can swell and bleed in response to the hormones, simulating a heat cycle.
You do not have to worry about pregnancy even if the pet seems to go in heat. If the uterus was, in fact, removed, then there is no way that your pet can become pregnant.
Visit the Vet
Other possible situations could simulate a heat cycle. Your pet may have a vaginal or bladder infection. Take your pet to the veterinarian for an examination to find out exactly what is causing bleeding or a heat cycle.
Myths About Spayed Pets
Despite what you may have heard, it isn't necessary for your pet to go through one heat cycle or have a litter before she is spayed.
Spaying does not cause a pet to be fat or lazy. Unless there is another underlying medical condition, in most cases, overweight cats and dogs get that way because they are fed too much and/or receive too little exercise.