title: Resynchronization of estrus in beef cattle: ovarian function, estrus and fertility following progestin treatment and treatments to synchronize ovarian follicular development and estrus.
abstract: The objective was to optimize rebreeding of nonpregnant, previously inseminated beef cattle. In Experiment 1, 43 cows received a used intravaginal progesterone-releasing insert (IVPRI; Days 0-7) 12.3 d after ovulation and received concurrently no treatment, 100 microg gonadotropin releasing hormone (GnRH), 1 mg estradiol cypionate (ECP), or 150 mg progesterone. Emergence of a new ovarian follicular wave was most synchronous (P < 0.0001) in the GnRH group. In Experiment 2, 675 heifers were given GnRH or no treatment on Day 0, fed melengestrol acetate (MGA; 0.5 mg/head/d) from Days 0-5 (Day 0 = 13-14 d after timed insemination; TAI), given 0.5 mg ECP or nothing on Day 7, and reinseminated 6-12 h after onset of estrus. Estrus was more synchronous (P < 0.05) in heifers given GnRH versus no treatment on Day 0. In Experiment 3, 317 TAI heifers were resynchronized with either MGA or a used IVPRI with or without ECP on Day 7; estrus was more synchronous (P < 0.05) and pregnancy rates were higher (54.1% versus 39.2%, P < 0.05) in heifers given a used IVPRI than those fed MGA. For resynchronization of heifers, pregnancy rates were not significantly improved with GnRH treatment, but were higher with a used IVPRI than with MGA.
authors.affiliation: Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5B4.
authors.forename: Marcos G
authors.initials: MG
authors.lastname: Colazo
authors.forename: John P
authors.initials: JP
authors.lastname: Kastelic
authors.forename: Julie A
authors.initials: JA
authors.lastname: Small
authors.forename: Randy E
authors.initials: RE
authors.lastname: Wilde
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Ward
authors.forename: Reuben J
authors.initials: RJ
authors.lastname: Mapletoft
mesh_terms: D000282:Administration, Intravaginal; D000818:Animals; D001947:Breeding / Q000379:methods*; D002417:Cattle / Q000502:physiology*; D004343:Drug Implants; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D004973:Estrus Synchronization / Q000379:methods*; D005260:Female; D005298:Fertility / Q000187:drug effects*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D007315:Insemination, Artificial / Q000662:veterinary; D008552:Melengestrol Acetate / Q000494:pharmacology; D006080:Ovarian Follicle / Q000187:drug effects / Q000254:growth & development*; D011247:Pregnancy; D018873:Pregnancy Rate; D011374:Progesterone / Q000494:pharmacology; D011372:Progestins / Q000494:pharmacology*; D011897:Random Allocation; D012098:Reproduction / Q000187:drug effects / Q000502:physiology; D013997:Time Factors
chemical_list: D004343:Drug Implants; D011372:Progestins; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D004958:Estradiol; D008552:Melengestrol Acetate; C007630:estradiol 17 beta-cypionate