Estrogen Toxicity in Small Mammals

Estrogen Toxicity in Small Mammals

Like cats, ferrets are induced ovulators. This means that the act of mating is required in order to stimulate ovulation. In order to keep the ferret in estrus and receptive to the male, high levels of estrogen are maintained. Unfortunately, ferrets are extremely sensitive to the effects of estrogen and toxicity readily develops.

Estrogen toxicity most often develops in ferrets that remain in estrus (heat) for over one month. The primary effect of high levels of estrogen is damage to the bone marrow. The ferret gradually becomes anemic and the white blood cell and platelet counts decrease since the bone marrow is no longer able to maintain normal levels of these cells.

What To Watch For

  • Lethargy
  • Pale gums
  • Bleeding
  • Persistent infections
  • Hair loss
  • Prolonged swelling of the vulva


    Your veterinarian will want to perform some tests to help with the diagnosis.

  • Early on, a CBC reveals a decreased red cell and platelet count, and a normal or increased white blood cell count. Later on, the white cells are decreased as well.
  • Bone marrow aspirate and cytology to confirm hypocellular (decreased cell) content.


    The optimal treatment for estrogen toxicity is to remove the source of the estrogen. By spaying the ferret, the levels of estrogen rapidly decrease and the bone marrow can begin to heal.

    For severely anemic ferrets, blood transfusions and supportive care may be necessary to stabilize the ferret before surgery. In some cases, hormonal therapy is used to induce ovulation and lower the estrogen levels. As soon as the ferret is stable, spaying performed.

    Home Care and Prevention

    There is no home care for estrogen toxicity. If you ferret is under treatment, make sure to give medications as directed. Since most ferrets are spayed before being adopted, the risk of estrogen toxicity is quite low. If you intend to breed your ferret, be aware that allowing your ferret to remain in heat may risk her life. A rigid breeding program should be established and followed.

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