EN
Prolactin (PRL) is known for the diverse role it plays in the preparation, maintenance and secretor activity of the mammary glands during lactation. It plays a role in processes such reproduction, fat metabolism, hair shedding and immune response. In humans, prolactin is able to inhibit GnRH secretion and has an antagonistic activity on ovarian function in comparison to GnRH. The role of prolactin during the estrous cycle has not been established, although there are few reports on increased follicular growth in anestrous mares, which have been administered prolactin. In mares, prolactin concentration is related to the length of daylight photoperiod periods, and its highest concentrations coincide with periods of maximum reproductive activity.