It is frequently desirable to prevent animals from engaging in breeding or to prevent pregnancy which may result from breeding. One of the most common methods of preventing pregnancy in animals, particularly pets, is the spaying or ovarihysterectomy (removal of uterus and ovaries) of a female and neutering or castration (removal of the testicles) of a male animal. However, these methods result in the permanent inability of the female animal to become pregnant or the male animal to impregnate a female animal. Under some circumstances, it may be desirable to prevent breeding between animals for a period of time, after which impregnation of the female animal may be desired.