Abstract
Blood samples were taken from five Holstein heifers at 2- to 6-hr. intervals from 4 days before estrus until ovulation to relate levels of LH and prolactin to behavioral and ovarian changes. Serum LH began a nonsignificant continuous rise 5 days before estrus, concluded by a burst (P<.01) of LH 19 times greater than the baseline; the peak preceded onset of standing heat by 3 hours. Serum LH was elevated for 6 to 8 hr. and ovulation occurred 32 hr. after the LH peak. Within 4 to 6 hr. after the peak, serum LH returned to pre-estrual levels and remained with little variance at that baseline for the remainder of the study (3 days). Prolactin, more variable than LH within heifers, was elevated (P≃.08) during estrus and declined during the 2 days following estrus. Copyright © 1971. American Society of Animal Science . Copyright 1971 by American Society of Animal Science.