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Abstract The objective of this experiment was to determine if ovarian hormone feedback on luteinizing hormone (LH) secretion is operative from completion of the preovulatory LH surge to resumption of luteal function in cattle; i.e., when serum progesterone concentrations are less than 1 ng/ml. At 16 hr after onset of estrus, five heifers were ovariectomized and five left intact. In addition, four heifers were ovariectomized during diestrus (Day 14, 15 or 16). Time 0 was either time of ovariectomy or 16 hr after onset of estrus. Blood collection periods were at-1 hr, then at 8-hr intervals for 96 hours. During the first hour of each period, jugular blood was collected every 15 min for 1 hour. Following estrus, progesterone in serum of intact heifers was less than . 3 ng/ml from time 0 to 48 hr then increased linearly to 1 ng/ml at 96 hours. In heifers ovariectomized after estrus serum progesterone was less than .3 ng/ml through 96 hours. In diestrous heifers serum progesterone averaged 5,4 ± 1.4 at 0 hr, decreased to .6 ± .2 by 8 hr after ovariectomy and averaged .2 ± .03 from 16 to 96 hours. Following estrus, serum LH increased (P<.01) linearly from 8 to 48 hr in both intact and ovariectomized heifers at rates of 22 and 21 pg/ml hr, respectively. Serum LH in ovariectomized heifers continued to increase at the same rate from 48 to 96 hr while that of intact heifers decreased (P<.05). Ovariectomy during diestrus caused serum LH to increase from .9 ng/ml at 0 hr to 5.4, 5.2 and 5.4 ng/ml at 8, 16 and 24 hours. Thereafter, serum LH decreased gradually but remained greater than 3 ng/ml throughout the 96-hr sampling period. These results indicate that negative feedback on LH release is probably not operative 0 to 48 hr post-estrus but is restored coincident with resumption of luteal function. Copyright © 1977. American Society of Animal Science. Copyright 1977 by American Society of Animal Science.