title: Effect of melengestrol acetate (MGA) or progesterone-releasing intravaginal device (PRID) on follicular development, concentrations of estradiol-17 beta and progesterone, and luteinizing hormone release during an artificially lengthened bovine estrous cycle.
abstract: Two trials were conducted to determine whether 7-d progestogen treatment beginning on d 17 of the estrous cycle altered 1) ovarian follicular development, 2) serum concentration of estradiol-17 beta (E2) and progesterone (P4), and 3) patterns of release of luteinizing hormone (LH). In both trials, Angus, Angus x Holstein, or Holstein cows 2 to 6 yr of age were randomly assigned to receive either melengestrol acetate (MGA, .5 mg.animal-1.d-1; n = 23), a progesterone-releaseing intravaginal device (PRID, n = 26) or to serve as untreated Controls (n = 14). Ultrasonography and blood sampling were performed daily throughout the experiment beginning on d 3 (Trial 1) or d 9 (Trial 2) of the estrous cycle. In Trial 2, blood samples were collected every 15-min for 6 h on d 17 (all cows) and d 20 and 23 (MGA and PRID cows) for determination of LH. Estrous cycle length was 3 to 5 d greater (P < .05) for MGA- and PRID-treated cows characterized by two (MGA-2 and PRID-2) or three (MGA-3 and PRID-3) dominant follicles than for control cows exhibiting two (Control-2) or three (Control-3) dominant follicles. A greater proportion (P < .05) of MGA- than of PRID-treated cows ovulated the follicle that was dominant at the beginning of treatment on d 17 (10 of 23 vs 1 of 26). Serum P4 concentrations declined 3 d earlier in Control-2 and MGA-2 cows than in Control-3, MGA-3 or PRID-3 cows.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Animal and Poultry Sciences, Virginia Polytechnic Institute & State University, Blacksburg 24061.
authors.forename: E E
authors.initials: EE
authors.lastname: Custer
authors.forename: W E
authors.initials: WE
authors.lastname: Beal
authors.forename: S J
authors.initials: SJ
authors.lastname: Wilson
authors.forename: A W
authors.initials: AW
authors.lastname: Meadows
authors.forename: J G
authors.initials: JG
authors.lastname: Berardinelli
authors.forename: R
authors.initials: R
authors.lastname: Adair
mesh_terms: D000282:Administration, Intravaginal; D000284:Administration, Oral; D000818:Animals; D002417:Cattle / Q000097:blood / Q000502:physiology*; D004958:Estradiol / Q000097:blood; D004971:Estrus / Q000097:blood / Q000187:drug effects*; D005260:Female; D016018:Least-Squares Analysis; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism; D008552:Melengestrol Acetate / Q000008:administration & dosage / Q000494:pharmacology*; D006080:Ovarian Follicle / Q000187:drug effects* / Q000502:physiology; D011374:Progesterone / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*
chemical_list: D011374:Progesterone; D004958:Estradiol; D008552:Melengestrol Acetate; D007986:Luteinizing Hormone