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Heifers experienced either a: 1) large magnitude of change in progesterone; 2) medium magnitude of change in progesterone; or 3) small magnitude of change in progesterone. During the 24 hours following the progesterone shift, heifers with the large magnitude progesterone shift had a greater LH pulse frequency than heifers with a medium or small magnitude of shift in progesterone. Despite the large or medium magnitude progesterone shift, LH pulse frequency did not differ from heifers in which a small change in progesterone occurred. We conclude that amount of progesterone in circulation is more important in regulation of LH secretion than magnitude of shift in amount of progesterone.