title: Effect of administration of human chorionic gonadotropin after artificial insemination on concentrations of progesterone and conception rates in beef heifers.
abstract: The objective of this study was to determine whether administration of hCG approximately 5 d after AI would increase plasma progesterone concentrations and conception rates in beef heifers. Heifers from two locations (Location 1: n = 347, BW = 367 +/- 1.72 kg; Location 2: n = 246, BW = 408 +/- 2.35 kg) received melengestrol acetate (0.5 mg.heifer(-1).d(-1)) for 14 d and an injection of PGF2alpha (25 mg i.m.) 19 d later. Heifers were observed for estrus continuously during daylight from d 0 to 4.5 after PGF2alpha and artificially inseminated approximately 12 h after the onset of estrus. Half of the heifers inseminated at Location 1 were assigned randomly to receive an injection of hCG (3,333 IU i.m.) 8 d after PGF2alpha, and a blood sample was collected from all heifers 14 d after PGF2alpha for progesterone analysis. Half of the heifers inseminated at Location 2 were administered hCG on d 9 after PGF2alpha, and a blood sample was collected from all heifers 17 d after PGF2alpha. Heifers at Location 1 had a 94% synchronization rate, exhibited estrus 2.45 +/- 0.03 d after PGF2alpha, and received hCG 5.55 +/- 0.03 d after AI. Heifers at Location 2 had an 85% synchronization rate, exhibited estrus 2.69 +/- 0.03 d after PGF2alpha, and received hCG 6.31 +/- 0.03 d after AI. Progesterone concentrations were greater (P < 0.01) for hCG-treated heifers than for controls at both locations (8.6 vs. 4.6 ng/mL for treatment vs. control at Location 1, and 11.2 vs. 5.6 ng/mL for treatment vs. control at Location 2). Pregnancy status was determined by ultrasound approximately 50 d after AI. Conception rates (65 vs. 70% for treatment vs. control, respectively) did not differ at Location 1. Conception rates tended (P = 0.10) to be increased with hCG treatment at Location 2 (61 vs. 50% for treatment vs. control, respectively). A second experiment was conducted with 180 heifers at a third location to determine the effects of hCG administration 6 d after timed insemination at approximately 60 h after PGF2alpha in heifers synchronized as in Exp. 1. Pregnancy rate to timed AI did not differ between hCG-treated (62%) and control heifers (59%). Final pregnancy rate after timed AI and bull exposure (92%) was not affected by treatment. In summary, administration of hCG 5 to 6 d after AI did not improve conception or pregnancy rates at two out of three locations evaluated, suggesting insufficient progesterone is not a major factor contributing to early pregnancy failure in beef heifers.
authors.affiliation: University of Nebraska, West Central Research and Extension Center, North Platte, 69101, USA. rfunston2@unl.edu
authors.forename: R N
authors.initials: RN
authors.lastname: Funston
authors.forename: R J
authors.initials: RJ
authors.lastname: Lipsey
authors.forename: T W
authors.initials: TW
authors.lastname: Geary
authors.forename: A J
authors.initials: AJ
authors.lastname: Roberts
mesh_terms: D000818:Animals; D002417:Cattle / Q000097:blood / Q000502:physiology*; D016009:Chi-Square Distribution; D006063:Chorionic Gonadotropin / Q000008:administration & dosage / Q000494:pharmacology*; D004971:Estrus / Q000502:physiology; D004973:Estrus Synchronization; D005260:Female; D005306:Fertilization / Q000187:drug effects*; D007315:Insemination, Artificial / Q000662:veterinary*; D011247:Pregnancy; D018873:Pregnancy Rate; D011374:Progesterone / Q000097:blood*; D011897:Random Allocation
chemical_list: D006063:Chorionic Gonadotropin; D011374:Progesterone