Spaying (the removal of the ovaries and uterus) is a veterinary procedure performed under general anesthesia that usually requires minimal hospitalization. Spaying a female cat or dog helps prevent pyometra (pus-filled uterus.) Treatment of pyometra requires hospitalization, intravenous fluids, and antibiotics. It also prevents breast cancer, which can be a result of malignant mammary tumors. More than 25% of unspayed female animals can develop mammary tumors in their lifetime. Mammary tumors can become malignant in about 50% of female dogs and 85% of female cats. Spaying your pet before her first heat offers the best protection from these diseases.