Synchronizing estrus in gilts and sows increases breeding scheduling efficiency and predictability, and can be achieved by using hormonal control products. During estrus, gonadotropin releasing hormone (GnRH) triggers the release of gonadotropins (FSH and LH), then ovary follicles grow and release estrogen, which results in estrus behaviours and increased GnRH. The GnRH then increases LH, and ova are released (ovulation). The eggs form a corpus luteum, which releases progesterone that inhibits FSH and LH. If fertilization does not occur, prostaglandin-F2α will be released, the corpus luteum regresses, and the estrus cycle begins again. PG 600 is made of equine and human chorionic gonadotropins (eCG and hCG) and triggers estrus cycling through its effect on FSH and LH. ECG can also be used alone to induce estrus through FSH, and GnRH or porcine luteinizing hormone (pLH) can be used to synchronize ovulation through their effect on LH. PGF2α can be used to synchronize estus, abort early pregnancies, or induce farrowing. Altrenogest is a progestin which suppresses gonadotropins, this allows for synchronization of estrus if fed until 5 days before the desired breeding dates.