05-19-2010, 05:15 PM
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Mares are also put under lights to encourage them to come into season earlier in the year, especially TBs, where the competitive advantage of a January birthday is huge. Mares normally don't cycle in Jan/Feb. Coat growth and a mare's heat cycle are both triggered by Circadian cycles, the seasonal fluctuation in the amount of daylight and dark. So putting horses in stalls with lights on timers to fool their bodies into thinking it's spring by the length of daylight keeps them from growing winter coats and brings mares into season.