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What is the normal estrous cycle length?

Last Updated: July 19, 2006

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During the normal physiological breeding season of the mare in North America, the average length of the estrous cycle is 21 to 23 days. Cycles vary from 7 to 175 days and are influenced most by season of the year. Approximately 50 to 60 percent of all mares have a cycle of 21, 22 or 23 days.

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