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This Article Full Text Full Text (PDF) All Versions of this Article: jas.2006-592v1 85/4/937    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Mussard, M. L. Articles by Day, M. L. Search for Related Content PubMed PubMed Citation Articles by Mussard, M. L. Articles by Day, M. L.

Influence of premature induction of a luteinizing hormone surge with gonadotropin-releasing hormone on ovulation, luteal function, and fertility in cattle¹

Department of Animal Sciences, The Ohio State University, Columbus 43210-1095

⁵ Corresponding author: day.5{at}osu.edu

We tested the hypothesis that luteal function and fertility would be reduced in cattle induced to ovulate prematurely compared with those ovulating spontaneously. Estrus was synchronized in 56 beef cows (24 that were nonlactating and 32 that were nursing calves). At 6.4 ± 0.1 d after estrus, all follicles 5 mm were aspirated (day of aspiration = d 0) with a 17-gauge needle using the ultrasound-guided transvaginal approach. On d 1.5 and 2, cows were administered 2 luteolytic doses of PGF₂. Ovarian structures were monitored by transrectal ultrasonography from d –2 to 12, or ovulation. Emergence of a new follicular wave occurred on d 1.7 ± 0.1. When the largest follicle of the newly emerged wave was 10 mm in diameter (d 4.8 ± 0.1), cows were assigned on an alternating basis to receive 100 µg of GnRH (GnRH-10; n = 29) to induce ovulation or, upon detection of spontaneous estrus, to the spontaneous (SPON) treatment (n = 24). Cows were bred by AI at 12 h after GnRH (GnRH-10) or 12 h after the onset of estrus (SPON) as detected using an electronic surveillance system. Blood samples were collected every other day beginning 2 d after ovulation until pregnancy diagnosis 30 d after AI. Ovulation and AI occurred in 29/29 cows in the GnRH-10 and in 24/24 cows in the SPON treatment. Ovulation occurred later (P < 0.05) in the SPON (d 7.7 ± 0.1) than GnRH-10 (d 6.8 ± 0.1) treatment. Double ovulations were detected in 47% of cows, resulting in 1.5 ± 0.1 ovulations per cow. Diameters of the ovulatory and the second ovulatory (in cows with 2 ovulations) follicles were greater (P < 0.05) in the SPON (12.0 ± 0.3 mm and 10.5 ± 0.4 mm, respectively) than in the GnRH-10 (10.7 ± 0.1 mm and 9.2 ± 0.3 mm) treatment. Cross-sectional areas of luteal tissue and plasma concentrations of progesterone during the midluteal phase were greater (P < 0.05) in the SPON (3.62 ± 0.2 cm² and 6.4 ± 0.3 ng/mL) than in the GnRH-10 (3.0 ± 0.2 cm² and 5.4 ± 0.2 ng/mL) treatment. The conception rate to AI in the SPON (100%) treatment was greater (P < 0.05) than in the GnRH-10 (76%) treatment. The animal model used in this study resulted in unusually high conception rates and double ovulations. In conclusion, premature induction of the LH surge reduced the diameter of ovulatory follicle(s), the luteal function, and the conception rate to AI.

Key Words: cattle • corpus luteum • fertility • ovarian follicle

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				M P Palhao, M A Beg, M T Rodrigues, and O J Ginther Follicle and hormone dynamics in single versus double ovulating heifers Reproduction, September 1, 2009; 138(3): 561 - 570. [Abstract] [Full Text] [PDF]