Objectives were to characterize changes in concentrations of LH, FSH, and estradiol-17beta (estradiol) in blood and populations of ovarian follicles of prepubertal cattle during waves of follicular development and to evaluate interactions between day after follicular aspiration and month prepuberty for these variables. During each month (month prepuberty), ovarian follicles of prepubertal cattle were aspirated to induce synchronous emergence of a wave of follicular development (day after follicular aspiration). Characteristics of ovarian follicular development and concentrations of hormones in blood were evaluated during the synchronous wave of follicular growth. Multiple regression was used to estimate hormonal variables and evaluate interactions for variables between day after follicular aspiration and month prepuberty. There were no interactions between day after follicular aspiration and month prepuberty for numbers of follicles 5 mm or concentrations of LH, FSH, and estradiol. The pattern of change in these variables after follicular aspiration was, therefore, similar each month prepuberty. There were interactions between day after follicular aspiration and month prepuberty for frequency and amplitude of LH pulses and size of largest follicle. There were also endocrine changes that were related to follicular development after follicular aspiration throughout the peripubertal period.

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The influence of episodic LH pulses before and subsequent to ovulation on size and function of the corpus luteum (CL) in cattle was examined. Treatments were 1) control; 2) LHRH antagonist starting 2 days before the preovulatory LH surge (Antagonist [Ant] -2); 3) LHRH antagonist at initiation of the preovulatory LH surge (Ant 0); and 4) LHRH antagonist starting 2 days after the preovulatory LH surge (Ant 2). Treatments with an LHRH antagonist were continued until 7 days after the preovulatory surge. Diameter of the CL and concentrations of progesterone were monitored during the luteal phase that ensued after treatment. Maximum average diameters of CL were 9.5, 17.5, 21.6, and 28.8 mm for females from the Ant -2, Ant 0, Ant 2, and control groups, respectively (P < 0. 01). Compared with those in control animals, concentrations of progesterone in plasma were less (P < 0.01) in animals in which release of LH pulses was inhibited by treatment with antagonist. Arbitrary units under the curve for concentrations of progesterone during the luteal phase of the estrous cycle for Ant -2, Ant 0, Ant 2, and control groups were 19.6, 41.6, 43.6, and 142.2, respectively. There was no difference in circulating concentrations of progesterone (P > 0.1) among antagonist-treated groups. In conclusion, episodic release of LH pulses before, during, and after the time of the preovulatory surge of LH may stimulate development and function of the CL in cattle.

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