title: The use of progestins in regimens for fixed-time artificial insemination in beef cattle.
abstract: Four experiments were conducted to investigate modifications to gonadotropin releasing hormone (GnRH)-based fixed-time Al protocols in beef cattle. In Experiment 1, the effect of reducing the interval from GnRH treatment to prostaglandin (PGF) was examined. Lactating beef cows (n = 111) were given 100 mg gonadorelin (GnRH) on Day 0 (start of treatment) and either 500 microg cloprostenol (PGF) on Day 6 with Al and 100 microg GnRH 60 h later, or PGF on Day 7 with Al and GnRH 48 h later (6- or 7-day Co-Synch regimens). Pregnancy rates were 32/61 (53.3%) versus 26/50 (52.0%), respectively (P = 0.96). In Experiment 2. cattle (n = 196) were synchronized with a 7-day Co-Synch regimen and received either no further treatment or a CIDR-B device (Days 0-7). Pregnancy rates were 32/71 (45.1%) versus 33/77 (42.9%) in cows (P < 0.8), and 9/23 (39.1 %) versus 17/25 (68.0%) in heifers (P < 0.05). In Experiment 3, 49 beef heifers were randomly assigned to receive 12.5 mg pLH on Day 0, PGF on Day 7 and 12.5 mg of pLH on Day 9 with Al 12 h later (pLH Ovsynch), or similar treatment plus a CIDR-B device from Days 0 to 7 (pLH Ovsynch + CIDR-B), or 1 mg estradiol benzoate (EB) and 100 mg progesterone on Day 0, a CIDR-B device from Days 0 to 7 (EB/ P4 + CIDR-B), PGF on Day 7 (at the time of CIDR-B removal) and 1 mg i.m. EB on Day 8 with AI on Day 9 (52 h after PGF). Pregnancy rate in the EB/P4 + CIDR-B group (75.0%) was higher (P < 0.04) than in the pLH Ovsynch group (37.5%): the pLH Ovsynch + CIDR-B group was intermediate (64.7%). In Experiment 4, 266 non-lactating cows were allocated to a 7-day Co-Synch protocol (Co-Synch), a 7-day Co-Synch plus 0.6 mg per head per day melengestrol acetate (MGA) from Days 0 to 6 inclusive (Co-Synch + MGA) or MGA (Days 0-6) plus 2 mg EB and 50 mg progesterone on Day 0. 500 microg PGF on Day 7, 1 mg EB on Day 8 and fixed-time Al 28 h later (EB/ P4 + MGA). Pregnancy rates (P < 0.25) were 44.8% (39/87: Co-Synch), 47.8% (43/90; Co-Synch + MGA), and 60.7% (54/89: EB/P4 + MGA). In conclusion, a 6- or 7-day interval from GnRH to PGF in a Co-Synch regimen resulted in similar pregnancy rates in cows. The addition of a progestin to a Co-Synch or Ovsynch regimen significantly improved pregnancy rates in heifers but not in cows. Progestin-based regimens that included EB consistently resulted in high pregnancy rates to fixed-time Al.
authors.affiliation: Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Canada.
authors.forename: Marcelo F
authors.initials: MF
authors.lastname: Martínez
authors.forename: John P
authors.initials: JP
authors.lastname: Kastelic
authors.forename: Gregg P
authors.initials: GP
authors.lastname: Adams
authors.forename: Byrne
authors.initials: B
authors.lastname: Cook
authors.forename: Walter O
authors.initials: WO
authors.lastname: Olson
authors.forename: Reuben J
authors.initials: RJ
authors.lastname: Mapletoft
mesh_terms: D000818:Animals; D002417:Cattle; D003008:Cloprostenol / Q000008:administration & dosage; D004958:Estradiol / Q000008:administration & dosage / Q000031:analogs & derivatives*; D004972:Estrus Detection; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary*; D007774:Lactation; D007986:Luteinizing Hormone / Q000008:administration & dosage; D008552:Melengestrol Acetate / Q000008:administration & dosage; D011247:Pregnancy; D011258:Pregnancy Tests / Q000662:veterinary; D011374:Progesterone / Q000008:administration & dosage; D011372:Progestins / Q000008:administration & dosage*; D013997:Time Factors; D014463:Ultrasonography
chemical_list: D011372:Progestins; C074283:estradiol 3-benzoate; D007987:Gonadotropin-Releasing Hormone; D003008:Cloprostenol; D011374:Progesterone; D004958:Estradiol; D008552:Melengestrol Acetate; D007986:Luteinizing Hormone