Overproduction of Estrogen in Dogs

Estrogen is one of the primary female sex hormones in dogs. Estrogen develops and maintains the female sexual organs and secondary sex characteristics. It is also responsible for normal sexual behavior. Overproduction of estrogen is known as hyperestrogenism or estrogen toxicity. Overproduction of this hormone can be due to an underlying body condition or it may be due to artificially induced estrogen hormone.

Sometimes, estrogen causes abnormal (cystic) cells to line the uterus which permits invasion of bacteria from vagina. The cervix is open during "heat" but if it is closed, it can lead to a serious infection (Pyometra – pus in uterus). Moreover, concentration of estrogen can result in infertility and/or imbalance in the blood.


Common symptoms associated with estrogen toxicity include:

Weakness (lethargy)

Pale gums

Bleeding—skin, urine, stool, vomit


Persistent infections

Thinning of the hair

Female characteristics in males


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


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