Effects of estradiol cypionate (ECP) on ovarian follicular dynamics, synchrony of ovulation, and fertility in CIDR-based, fixed-time AI programs in beef heifers.
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.
Colazo
Marcos Germán
MG
Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, 52 Campus Drive, Saskatoon, SK, Canada S7N 5B4.
Kastelic
John Patrick
JP
Mapletoft
Reuben John
RJ
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
D004343:Drug Implants; D011460:Prostaglandins F; D011374:Progesterone; D004958:Estradiol; C007630:estradiol 17 beta-cypionate; D007986:Luteinizing Hormone