Light Effects on Melatonin and GnRH
Season dramatically effects reproduction in the mare. The effects of season are mediated by changing day length. During the winter, long nights lead to high levels of melatonin. These high melatonin levels suppress GnRH production by the hypothalamus and shut down reproduction. During the spring, the increasing day length and decreasing length of the night, lead to reduced melatonin and increased GnRH that initiates estrous cycles.
