title: The use of a progesterone-releasing device (CIDR-B) or melengestrol acetate with GnRH, LH, or estradiol benzoate for fixed-time AI in beef heifers.
abstract: The objective of this experiment was to compare two progestins and three treatments for synchronizing follicular wave emergence and ovulation in protocols for fixed-time AI in beef heifers. On d 0 (beginning of the experiment), Angus and Angus-Simmental cross beef heifers at random stages of the estrous cycle either received a CIDR-B device (n = 257) or were started on 0.5 mg x anima(-1) x d(-1) melengestrol acetate (MGA; n = 246) and were randomly assigned to receive i.m. injections of 100 microg GnRH, 12.5 mg porcine LH (pLH), or 2 mg estradiol benzoate (EB) and 50 mg progesterone (P4). The last feeding of MGA was given on d 6 and on d 7, CIDR-B devices were removed and all heifers received 500 microg cloprostenol (PG). Consistent with their treatment groups on d 0, heifers were given either 100 microg GnRH or 12.5 mg pLH 48 h after PG (and were concurrently inseminated) or 1 mg EB 24 h after PG and were inseminated 28 h later (52 h after PGF). Estrus rate (combined for both progestins) in heifers receiving EB (92.0%) was greater (P < 0.05) than that in heifers receiving GnRH and pLH (combined) and a CIDR-B device (62.9%) or MGA (34.3%). Although the mean interval from PG treatment to estrus did not differ among groups (overall, 47.8 h; P = 0.85), it was less variable (P < 0.01) in MGA-fed heifers (SD = 2.5 h) than in CIDR-B-treated heifers (SD = 8.1 h). Pregnancy rates (determined by ultrasonography approximately 30 d after AI) did not differ (P = 0.30) among the six treatment groups (average, 58.0%; range, 52.5 to 65.0%). Although fixed-time AI was done, pregnancy rates were greater in heifers detected in estrus than in those not detected in estrus (62.6 vs 51.9%; P < 0.05). In conclusion, GnRH, pLH, or EB treatment in combination with a CIDR-B device or MGA effectively synchronized ovulation-for fixed-time AI, resulting in acceptable pregnancy rates in beef heifers.
authors.affiliation: Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Canada.
authors.forename: M F
authors.initials: MF
authors.lastname: Martinez
authors.forename: J P
authors.initials: JP
authors.lastname: Kastelic
authors.forename: G P
authors.initials: GP
authors.lastname: Adams
authors.forename: R J
authors.initials: RJ
authors.lastname: Mapletoft
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D003008:Cloprostenol; D004343:Drug Implants; D004958:Estradiol / Q000008:administration & dosage* / Q000031:analogs & derivatives*; D004973:Estrus Synchronization / Q000187:drug effects*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage; D007315:Insemination, Artificial / Q000662:veterinary*; D007986:Luteinizing Hormone / Q000008:administration & dosage; D008552:Melengestrol Acetate / Q000008:administration & dosage; D010060:Ovulation; D011247:Pregnancy; D018873:Pregnancy Rate; D011374:Progesterone / Q000008:administration & dosage; D045167:Progesterone Congeners / Q000008:administration & dosage*
chemical_list: D004343:Drug Implants; D045167:Progesterone Congeners; C074283:estradiol 3-benzoate; D007987:Gonadotropin-Releasing Hormone; D003008:Cloprostenol; D011374:Progesterone; D004958:Estradiol; D008552:Melengestrol Acetate; D007986:Luteinizing Hormone