Yes, dogs produce estrogen naturally, and it plays important roles in both female and male dogs. The ovaries are the primary source in females, but smaller amounts are also made by the testicles, adrenal glands, placenta, liver, muscle, fat, and even hair follicles. Estrogen affects far more than reproduction: it influences bone marrow function, urinary tract health, and hormone signaling in the brain.
Where Estrogen Comes From in Dogs
In intact female dogs, the ovaries are the main estrogen factory. Production ramps up during the heat cycle and drops off between cycles. Male dogs produce estrogen too, primarily through a process in which their bodies convert testosterone into estradiol (the most active form of estrogen) using an enzyme called aromatase. The testicles contribute directly as well, though in much smaller quantities than ovaries do during a heat cycle.
The adrenal glands, which sit near the kidneys, produce small amounts of estrogen in both sexes. This becomes relevant after spaying or neutering, when the gonads are removed and the adrenal glands remain the only internal source.
Estrogen During the Heat Cycle
A female dog’s heat cycle has distinct hormonal phases, and estrogen drives the first one. During proestrus, the stage when you first notice vulvar swelling and bloody discharge, the ovaries steadily increase estrogen output. Levels peak one to two days before the dog enters estrus, the phase when she’s actually fertile and receptive to mating.
Once estrus begins, estrogen drops and progesterone takes over. This hormonal handoff triggers the surge of luteinizing hormone that causes ovulation. After ovulation, during the phase called diestrus, progesterone dominates for roughly two months whether or not the dog is pregnant. Estrogen stays low throughout this period. This cycling pattern repeats roughly every six to eight months in most breeds, though the interval varies.
What Estrogen Does in Male Dogs
Estrogen isn’t just a “female hormone.” In male dogs, the conversion of testosterone to estradiol in the brain is a necessary step for regulating reproductive hormones. Research from studies using castrated dogs showed that blocking this conversion with an aromatase inhibitor prevented testosterone from doing its usual job of controlling luteinizing hormone levels. In other words, the male brain needs estradiol, derived from testosterone, to keep its own hormonal feedback loop working properly.
Under normal circumstances, male dogs maintain low but steady estrogen levels without any issues. Problems arise only when estrogen becomes abnormally elevated, most commonly from certain testicular tumors.
Estrogen-Producing Tumors in Males
A type of testicular tumor called a Sertoli cell tumor can secrete large amounts of estrogen, causing a condition known as feminization syndrome. Between 25% and 50% of male dogs with this tumor develop visible signs: symmetrical hair loss on both flanks, darkening skin, breast tissue enlargement, and swelling of the prepuce. These dogs essentially show the physical effects of estrogen overload.
The more dangerous consequence is what excess estrogen does to bone marrow. High estrogen levels are toxic to the cells that produce blood components, leading to a condition called estrogen-induced myelotoxicity. This shows up as severe anemia, dangerously low platelet counts, and abnormal white blood cell levels. Cryptorchid dogs, those with one or both undescended testicles, face a higher risk of developing Sertoli cell tumors, which is one reason veterinarians recommend neutering cryptorchid males.
What Happens to Estrogen After Spaying
When a female dog is spayed (ovariohysterectomy), the ovaries are removed and estradiol levels drop significantly. The adrenal glands continue producing trace amounts of related hormones, but they don’t compensate meaningfully for the lost ovarian output.
This estrogen drop has a well-documented effect on the urinary tract. Estrogen helps keep the urethral sphincter, the muscle that holds urine in, responsive and toned. After spaying, the loss of estradiol causes the urethral closure mechanism to weaken, typically within three to six months. This is why some spayed females develop urinary incontinence, often noticed as urine leaking during sleep. Larger breeds are especially prone. The condition responds well to treatment because giving low-dose estrogen restores the sphincter’s sensitivity to the nerve signals that keep it closed.
Normal Estrogen Levels in Dogs
Blood estradiol concentrations in intact female dogs fluctuate considerably depending on the stage of the reproductive cycle. One study tracking healthy dogs over several weeks found estradiol levels ranging from about 45 to 120 pg/mL, with an average around 70 pg/mL. Levels were higher in the earlier weeks of measurement (around 72 to 77 pg/mL) and declined to about 63 pg/mL by week six. These numbers matter mostly to veterinarians trying to determine whether an intact female’s estrogen is abnormally high, such as when investigating an ovarian cyst or tumor.
Accidental Exposure to Human Estrogen Products
One practical concern for dog owners is accidental contact with human hormone replacement products. Topical estrogen creams and patches used by people can transfer to dogs through skin contact, licking, or chewing discarded patches. In dogs, doses greater than 1 mg per kilogram of body weight can be toxic.
Signs of external estrogen exposure include notable hair loss, vulvar swelling in females, genital shrinkage in males, weakness, and loss of coordination. Multiple case reports have documented dogs developing alopecia simply from regular contact with owners who applied topical hormone creams. If you use any form of topical estrogen, keep the application site covered and wash your hands thoroughly before handling your dog.
Estrogen Toxicity and Bone Marrow
Dogs are unusually sensitive to estrogen’s effects on bone marrow compared to many other species. Whether the source is an estrogen-secreting tumor, an ovarian cyst, or accidental ingestion of hormone medication, the result follows a predictable and dangerous pattern. Estrogen initially stimulates bone marrow, causing a temporary increase in certain white blood cells. Then it suppresses marrow function, reducing the production of red blood cells, white blood cells, and platelets all at once.
This condition, called aplastic anemia, can become life-threatening. The dog becomes weak and pale from anemia, vulnerable to infections from low white cell counts, and at risk of uncontrolled bleeding from insufficient platelets. Recovery depends on removing the estrogen source early enough for the bone marrow to regenerate. If caught before the marrow is severely damaged, most dogs recover over several weeks once estrogen levels normalize.