Signs of Heat (estrus) after spaying in Dogs

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Key takeaways

Estrus, or “heat,” is the period of a female dog’s reproductive cycle when she is most fertile and receptive to breeding.

  • Signs of estrus include a swollen vulva, bloody vaginal discharge, mammary enlargement, “nesting” behavior and attraction of male dogs
  • Sexual alteration (aka spaying) usually stops symptoms of estrus by removing the ovaries and uterus (the sex organs involved in regulating estrus)
  • When ovarian tissue remnants are left behind, estrus symptoms can return
  • Remnants might be left behind due to a surgical error, a high-risk patient having reduced tolerance for anesthesia, or ovarian tissue being present in abnormal locations
  • Exposure to estrogen (such as from human medications) can also cause heat-like symptoms
  • Diagnostics include medical history, blood work, vaginal cytology, and in some cases advanced imaging
  • Treatment is surgical removal of the ovarian remnant(s); referral to a board-certified surgeon may be recommended
  • Prognosis after treatment is excellent
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A closer look: Signs of Heat (estrus) after spaying in Dogs

Most female mammals have recurring periods of heat or estrus when they are in their optimal window for successful mating. The cycle of estrus is regulated by sex hormones, which are secreted by the ovaries at regular intervals. When a female dog is sexually altered (spayed), the ovaries and uterus are removed, and estrus symptoms are expected to stop in the absence of ovarian tissue.

Symptoms of continued estrus after spaying are similar to the signs of estrus prior to spaying. If ovarian tissue remnants remain, estrus behavior is expected to occur approximately every six months.

Some dogs show signs of a false pregnancy which include mammary development, lactation, and behavioral changes such as nesting and hiding. Pregnancy is not possible since the uterus is no longer present, but the dog’s body goes through the same hormonal changes as if it was.

Prognosis is excellent with removal of the remaining ovarian tissue, but treatment does require surgery if the cause is remaining ovarian tissue.

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Possible causes

An ovarian tissue remnant that remains in the abdomen after spaying is the most common cause or estrus after spay surgery. A routine spay usually involves removing both the ovaries and the uterus. Rarely, ovarian remnants can be left behind due to surgical error. Factors like obesity and abnormal internal anatomy of the individual dog may lead to incomplete removal of all ovarian tissue. The remaining ovarian tissue continues to secrete sex hormones, leading to estrus symptoms just like it does in intact females.

Less common causes include the existence of ovarian tissue in places it is not expected to be, or accidental seeding of the abdomen with ovarian tissue during removal. Seeding the abdomen with ovarian tissue occurs when both ovaries are removed, but small amounts of ovarian tissue inadvertently drop back into the abdomen where it can continue to secrete sex hormones after the surgical procedure is complete.

Exposure to estrogen from an external source, such as an owner's estrogen cream, can also produce signs of estrus.

Other rare causes are an extra unknown ovary that is present, ovarian tissue elsewhere in the body, or an estrogen producing adrenal tumor.

Risk factors

Estrus symptoms in a spayed female dog are very uncommon. Signs of estrus are not life threatening, but if persistent heat after spaying is not addressed, it can eventually lead to complications.

If ovarian remnants are present after spay surgery, the time between sexual alteration and the return of estrus symptoms is variable. There is no age or breed disposition.

Other complications related to spay surgery can be life threatening. Dogs exhibiting vaginal discharge along with lethargy, vomiting, diarrhea, anorexia or increased thirst and urination need emergency veterinary attention.

Testing and diagnosis

Diagnosing the cause of estrus symptoms in a spayed dog requires a thorough history to rule out potential exposure to estrogen from an external source. If no exposure to estrogen is noted, an ovarian remnant is the most likely cause.

Diagnosing an ovarian remnant includes blood work, abdominal ultrasound, vaginal cytology, and occasionally advanced imaging such as an MRI or CT scan.

Treatment is surgical removal of the remaining ovarian tissue. Ovarian tissue remnants are often difficult to find and referral to a board certified surgeon for removal may be recommended.

Estrogen-producing adrenal tumors are rare in dogs, and may require additional testing.

Similar symptoms

Another situation that can be mistaken for heat is residual circulating hormones. If the spay procedure was performed while the pet was in heat, the already circulating hormones may take several weeks to dissipate and signs of estrus may persist until sex hormones have fully cleared the bloodstream. The symptoms should not return if all ovarian tissue was removed.

Associated symptoms

Symptoms of stump pyometra are a medical emergency.


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