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.
Some recent articles and even some veterinarians have begun to suggest that early spay/neuter can adversely affect large dogs' orthopedic growth. While this can sometimes be true for male dogs, the benefits far outweigh the risks, particularly for females. The VHS still advocates for spay/neuter surgery as young as possible. Read more on this research here.