Submitted to: Society for the Study of Reproduction Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: March 1, 2003
Publication Date: May 1, 2003
Citation: PERRY JR, G.A., SMITH, M.F., ROBERTS, A.J., MACNEIL, M.D., GEARY, T.W. EFFECT OF OVULATORY FOLLICLE SIZE AT TIME OF GNRH INJECTION ON PREOVULATORY SERUM CONCENTRATIONS OF ESTRADIOL IN BEEF COWS. SOCIETY FOR THE STUDY OF REPRODUCTION ANNUAL MEETING ABSTRACT #530. 2003. v. 68(1). p. 330. Technical Abstract: Follicles <12 mm in diameter that were induced to ovulate with GnRH resulted in increased embryonic mortality (days 27 to 68) compared to GnRH-induced ovulation of larger follicles, but follicle size in cows detected in standing estrus had no effect on embryonic mortality. Thus, our objective was to determine the relationship among follicle sizes at time of GnRH with concentrations of estradiol and progesterone in cows detected or not detected in standing estrus. Lactating beef cows (n = 273) were treated with 100 mcg GnRH on day -9, 25 mg PG on day -2, and 100 mcg GnRH at artificial insemination on day 0. Transrectal ultrasonography was performed on day 0 to determine ovulatory follicle size and on day 27 to determine pregnancy rate. Blood was collected on days -2, 0, and 13. Cows detected in standing estrus (+/- 12 hours of insemination) using Heatwatch (electronic mount detectors) had greater (P < 0.01) concentrations of estradiol at insemination than cows not detected in standing estrus. Cows diagnosed pregnant on day 27 had greater (P < 0.01) concentrations of estradiol at insemination than cows diagnosed not pregnant. Among cows not detected in standing estrus, concentrations of estradiol were greater (P < 0.02) at insemination in cows that ovulated >/=13 mm follicles compared to cows that ovulated </=11 mm follicles. Concentrations of progesterone on day 13 were greater (P < 0.05) in cows that ovulated >/=15 mm follicles compared to cows that ovulated </=12 mm follicles and were greater (P < 0.01) in cows diagnosed pregnant on day 27 compared to cows diagnosed not pregnant. Among cows detected in standing estrus, concentrations of estradiol at insemination did not differ (P = 0.30) among follicle sizes, and concentrations of progesterone on day 13 were not affected by follicle size (P = 0.61) or day 27 pregnancy status (P = 0.33). In summary, concentrations of estradiol in cows not detected in standing estrus were greater at time of GnRH injection in cows that ovulated >/=13 mm follicles, but concentrations of estradiol were similar among all follicle sizes in cows detected in standing estrus.