title: Effects of estradiol cypionate (ECP) on ovarian follicular dynamics, synchrony of ovulation, and fertility in CIDR-based, fixed-time AI programs in beef heifers.
abstract: Estradiol cypionate (ECP) was used in beef heifers receiving a controlled internal drug release (CIDR; insertion = Day 0) device for fixed-time AI (FTAI) in four experiments. In Experiment 1, heifers (n = 24) received 1mg ECP or 1mg ECP plus 50mg commercial progesterone (CP) preparation i.m. on Day 0. Eight or 9 days later, CIDR were removed, PGF was administered and heifers were allocated to receive 0.5mg ECP i.m. concurrently (ECP0) or 24h later (ECP24). There was no effect of treatment (P = 0.6) on mean (+/-S.E.M.) day of follicular wave emergence (3.9+/-0.4 days). Interval from CIDR removal to ovulation was affected (P<0.05) only by duration of CIDR treatment (88.3+/-3.8h versus 76.4+/-4.1h; 8 days versus 9 days, respectively). In Experiment 2, 58 heifers received 100mg progesterone and either 5mg estradiol-17beta or 1mg ECP i.m. (E-17beta and ECP groups, respectively) on Day 0. Seven (E-17beta group) or 9 days (ECP group) later, CIDR were removed, PGF was administered and heifers received ECP (as in Experiment 1) or 1mg EB 24h after CIDR removal, with FTAI 58-60h after CIDR removal. Follicular wave emergence was later (P<0.02) and more variable (P<0.002) in heifers given ECP than in those given E-17beta (4.1+/-0.4 days versus 3.3+/-0.1 days), but pregnancy rate was unaffected (overall, 69%; P = 0.2). In Experiment 3, 30 heifers received a CIDR device and 5mg E-17beta, with or without 100mg progesterone (P) i.m. on Day 0. On Day 7, CIDR were removed and heifers received ECP as described in Experiment 1 or no estradiol (Control). Intervals from CIDR removal to ovulation were shorter (P<0.05) in ECP0 (81.6+/-5.0h) and ECP24 (86.4+/-3.5h) groups than in the Control group (98.4+/-5.6h). In Experiment 4, heifers (n = 300) received a CIDR device, E-17beta, P, and PGF (as in Experiment 3) and after CIDR removal were allocated to three groups (as in Experiment 2), with FTAI 54-56h (ECP0) or 56-58h (ECP24 and EB24) after CIDR removal. Pregnancy rate did not differ among groups (overall, 63.6%, P = 0.96). In summary, although 1mg ECP (with or without progesterone) was less efficacious than 5mg E-17beta plus 100mg progesterone for synchronizing follicular wave emergence, 0.5mg ECP (at CIDR removal or 24h later) induced a synchronous ovulation with an acceptable pregnancy rate to fixed-time AI.
authors.affiliation: Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, 52 Campus Drive, Saskatoon, SK, Canada S7N 5B4.
authors.forename: Marcos Germán
authors.initials: MG
authors.lastname: Colazo
authors.forename: John Patrick
authors.initials: JP
authors.lastname: Kastelic
authors.forename: Reuben John
authors.initials: RJ
authors.lastname: Mapletoft
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D004343:Drug Implants; D004958:Estradiol / Q000008:administration & dosage* / Q000031:analogs & derivatives*; D005260:Female; D005298:Fertility / Q000187:drug effects*; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary*; D007986:Luteinizing Hormone / Q000097:blood; D006080:Ovarian Follicle / Q000187:drug effects* / Q000502:physiology; D010053:Ovary / Q000000981:diagnostic imaging; D010060:Ovulation / Q000187:drug effects*; D011247:Pregnancy; D011374:Progesterone / Q000008:administration & dosage; D011460:Prostaglandins F / Q000008:administration & dosage; D013997:Time Factors; D014463:Ultrasonography
chemical_list: D004343:Drug Implants; D011460:Prostaglandins F; D011374:Progesterone; D004958:Estradiol; C007630:estradiol 17 beta-cypionate; D007986:Luteinizing Hormone