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United States Department of Agriculture

Agricultural Research Service

Title: Effect of Ovulatory Follicle Size at Time of Gnrh Injection Or Standing Estrus on Pregnancy Rates and Embryonic/fetal Mortality in Beef Cattle

Authors
item Perry Jr, George
item Smith, M - UNIVERSITY OF MISSOURI
item Lucy, M - UNIVERSITY OF MISSOURI
item Roberts, Andrew
item Macneil, Michael
item Geary, Thomas

Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: April 1, 2003
Publication Date: June 1, 2003
Citation: PERRY JR, G.A., SMITH, M.F., LUCY, M.C., ROBERTS, A.J., MACNEIL, M.D., GEARY, T.W. EFFECT OF OVULATORY FOLLICLE SIZE AT TIME OF GNRH INJECTION OR STANDING ESTRUS ON PREGNANCY RATES AND EMBRYONIC/FETAL MORTALITY IN BEEF CATTLE. JOURNAL OF ANIMAL SCIENCE SUPPLEMENT ABSTRACT #211. 2003. v. 81(SUPPL. 1). p. 52.

Technical Abstract: Use of GnRH in AI protocols results in ovulation of a wide range of follicle sizes. Our objective was to determine the effect of ovulatory follicle size at GnRH-induced ovulation or standing estrus on pregnancy rates and embryonic/fetal mortality. Lactating beef cows (n = 273) received the CO-Synch protocol (100 ug GnRH, i.m. on d -9; 25 mg PG, i.m. on d -2; and 100 ug GnRH, i.m. on d 0 with timed AI) or were inseminated following detection of estrus using Heatwatch (electronic mount detectors). Ovulatory follicle size was determined by transrectal ultrasonography on d 0 (timed AI) or 12 h after detection in estrus. Pregnancy rates and fetal viability were determined by transrectal ultrasonography on d 27, 41, 55, and 68 after timed-insemination. On d 27 following GnRH-induced ovulation, there was a tendency (P = 0.07) for follicle size to effect pregnancy rates [13/45 (29%), 13/22 (59%), 18/39 (46%), 11/28 (39%), 13/20 (65%), and 7/19 (37%) for </= 11, 11.5 to 12, 12.5 to 13, 13.5 to 14, 14.5 to 15, and >/= 15.5 mm follicles; respectively]; however, by d 68 embryonic loss in cows that were induced to ovulate </= 11 mm follicles resulted in lower (P < 0.01) pregnancy rates (8/45; 18%) than cows in each of the other groups, which were unchanged from d 27. When ovulation occurred following standing estrus (37 d AI breeding season) there was no effect of follicle size (P = 0.18) on pregnancy rates at d 25 to 39 after insemination [11/14 (79%), 14/20 (70%), 28/35 (80%), 26/41 (63%), 21/25 (84%), and 25/38 (66%) for </= 11, 11.5 to 12, 12.5 to 13, 13.5 to 14, 14.5 to 15, and >/= 15.5 mm; respectively], nor were embryonic/fetal mortalities affected by ovulatory follicle diameter (P = 0.66). In summary, embryonic/fetal survival was decreased following GnRH-induced but not spontaneous ovulation of small (</= 11 mm) ovulatory follicles in beef cows.

Last Modified: 12/17/2014
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