gonadotropins secreted by the pituitary or the placenta in horses. This term generally refers to the gonadotropins found in the pregnant mare serum, a rich source of equine chorionic gonadotropin; LUTEINIZING HORMONE; and follicle stimulating hormone. Unlike that in humans, the equine luteinizing hormone, beta subunit is identical to the equine choronic gonadotropin, beta. Equine gonadotropins prepared from pregnant mare serum are used in reproductive studies.