For dogs....
An
ovariohysterectomy (OHE) or
spay is the complete removal of the
female reproductive tract. The ovaries, oviducts, uterine horns, and most of the body of the uterus are removed. Not only does this procedure prevent the animal from getting
pregnant but it also eliminates the twice-yearly
heat cycles. The
surgery removes the source of production of such hormones as
estrogen and
progesterone (primarily produced by the ovaries). These hormones are responsible for stimulating and controlling heat cycles and play a major role during pregnancy. But they also have other effects on the body and some of them are potentially harmful.