A variety of hormones are used within the dairy industry to treat reproductive disorders and to regulate the oestrous cycle for timed breeding. These hormones act directly on either the reproductive organs or on the pituitary gland itself to stimulate the release of naturally occurring hormones. These hormones then stimulate the reproductive organs. Prostaglandin, oestrogen and oxytocin act directly on the reproductive organs whereas gonadotrophic releasing hormone (GnRH) acts at the level of the pituitary gland.