ARS | Publication request: Influence of Exogenous Progestin on Ovarian Function in Beef Cows

Submitted to: Midwestern Section of the American Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: November 11, 2008
Publication Date: July 1, 2009
Citation: Cushman, R.A., Wood, J.R., Echternkamp, S.E., Cupp, A.S. 2009. Influence of Exogenous Progestin on Ovarian Function in Beef Cows [abstract]. Journal of Animal Science. 87 (E-Supplement 3):113 (Abstract # 239).

Technical Abstract: The ability to precisely regulate follicle recruitment and selection is critical to improving methods to control ovulation in beef cows. The objectives of the current study were to investigate the influence of exogenous progestins, commonly used in synchronization protocols, on ovarian function and determine if anti-Müllerian hormone (AMH) expression differed due to progesterone (P4) concentration. Low amounts of progestins have been reported to cause persistent follicles and decrease antral follicle number. Furthermore, AMH expression was found to be increased in the ovaries of women with cystic follicles. Therefore, we hypothesized that AMH would be increased in ovaries from cows treated with low levels of progesterone that developed persistent follicles. Beef cows (n = 12) were either 1) injected with GnRH (100 'g, i.m.) and a controlled intravaginal drug releasing (CIDR) device (4-6 ng/ml P4) inserted for 7 d or 2) cows (n = 13) were injected with prostaglandin and fed MGA (0.5 mg/kg/d; < 1 ng/ml P4) for 14 d. At CIDR removal, or removal of melengestrol acetate (MGA), prostaglandin (25 mg, i.m.) was administered and 36 h later, ovaries were examined by ultrasonography and removed by flank laparotomy. Ovaries were weighed, the length and width measured, and surface follicles were counted. The MGA decreased (P </= 0.05) the total number of follicles detectable by ultrasonography or surface count and increased the diameter of the largest follicle (P = 0.003). Real-time RT-PCR analysis revealed that AMH transcripts were significantly reduced in the ovarian cortex of MGA cows compared with CIDR cows (P < 0.05). Ovarian weight, length, and width did not differ between treatments. We conclude that persistent follicles in MGA-treated cows produce factors that negatively influence development of subordinate follicles. The decreased number of follicles results in decreased AMH expression in the ovarian cortex of cows with persistent follicles.