Overproduction of Estrogen in Dogs

By PetMD Editorial on Jul. 1, 2008

Hyperestrogenism in Dogs

Estrogen -- a type of hormone -- is naturally produced in female dogs. It is responsible for normal sexual behavior and development, and the customary biological function of the female reproductive tract. Overproduction of estrogen can result in what is known as estrogen toxicity (hyperestrogenism). This can happen without any outside interference or it can occur when estrogens are being introduced artificially.

Estrogens sometimes cause abnormal (cystic) cells to line the uterus and this permits the invasion of bacteria from the vagina. The cervix is open during "heat," but if it is closed it can lead to a serious infection (pyometra). In addition, a concentration of estrogen can result in infertility, as well as an imbalance in the blood.

Symptoms and Types

  • Weakness (lethargy)
  • Pale gums
  • Bleeding—skin, urine, stool, vomit
  • Fever
  • Persistent infections
  • Thinning of the hair
  • Female characteristics in males
  • Infertility
  • Prolonged estrus
  • Enlarged vulva
  • Enlarged teats in female
  • Decreased attraction to opposite sex
  • Excess attraction to opposite sex in females (nymphomania)
  • Bleeding from the vulva
  • Hair loss (alopecia)
  • Tumor on tail in male (stud dog tail)
  • Testicular mass in male
  • Testicular atrophy


  • Excessive production of estrogen
  • Administration of estrogen supplements
  • Ovarian cysts
  • Ovarian tumor
  • Testicular tumor



  • Complete blood count (CBC)
  • Bone marrow biopsy (aspirate)
  • X-ray of the abdomen
  • Ultrasound of the abdomen
  • Thorough examination of testicles in intact males
  • Needle biopsy (aspiration) of testicular masses
  • Ultrasound-guided aspiration of ovarian cysts
  • Biopsy of lymph nodes
  • Skin biopsy to determine cause of hair loss


  • Stop estrogen supplementation
  • Supportive care, including antibiotics and blood transfusions
  • Blood transfusions, if anemic
  • Antibiotics in case of infections
  • Masses may be examined via small scope instrument (laparoscopy)
  • Masses may be removed via incision (laparotomy)
  • If estrogen is not being administered artificially, surgical neutering in either male or female
  • Removal of testicle or ovary may be considered for valuable breeding animals
  • Testicular prosthetic devices are not advised
  • Medications to increase blood production in bone marrow
  • Medication to induce ovulation may be prescribed if there are cysts

Living and Management

Recovery may take a while -- up to several months -- so be prepared to provide long-term care for your pet. Be vigilant in providing prescribed medications and aware of any changes in your pet. Blood tests (and sometimes bone-marrow biopsies) must be performed to evaluate your pet's response to the therapy.

Do not give estrogen-containing compounds unless advised to by your veterinarian. Females will undergo tests to determine whether ovulation is occurring.

In addition, a male dog should not show signs of feminization once a testicular tumor has been removed.

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