When a cat is spayed (medically known as "ovariohysterectomy"), the ovaries, oviducts, and uterus are removed. The ovaries produce hormones which are responsible for the heat cycle in cats. Therefore when the cat is spayed, the heat cycle should stop. So how can a spayed cat come into heat?
In some cases, a small portion of the ovary is left behind and continues to produce hormones which trigger the heat cycle. When this occurs, she will continue to go into heat, but can not become pregnant. This is known as "ovarian remnant syndrome" (ORS).
So is the veterinarian at fault?
Not necessarily, in some cats, it is believed that they may have additional ovarian tissue underneath the ovary, which is missed during surgery.
Symptoms can occur days or years after surgery, there appears to be no breed predisposition. Signs of estrus can include:
- Calling (loudly).
- Being extra affectionate.
- She will often get into the mating stance, with the front half of her body lowered, and the rear part raised, she may tread her feet as she is doing this.
If she is allowed, she will mate at this time, while she will not be able to get pregnant, she is still at risk of catching FIV or FeLV by mating with the local tom.
How is ovarian remnant syndrome diagnosed?
Diagnosis is based on outward signs of estrus along with tests including:
- Vaginal smear, where a sample of the cells from the vaginal wall is taken and examined under a microscope. This must be done at the time of estrus and a positive result will show the presence of cornified vaginal epithelial cells.
- Testing for elevated estrogen and progesterone levels in blood serum.
- Ultrasound may reveal the presence of ovarian tissue, however, this may not always be visible on ultrasound.
How is ovarian remnant syndrome treated?
Surgical exploration to locate and remove the ovarian tissue. This is best performed when the cat is showing signs of heat as the ovarian tissue will be more visible.