|Funston, Richard - MONTANA STATE UNIVERSITY|
|Olson, J - MONTANA STATE UNIVERSITY|
|Lipsey, R - AMERICAN SIMMENTAL ASSOC.|
Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: April 1, 2003
Publication Date: June 1, 2003
Citation: FUNSTON, R.N., OLSON, J.L., LIPSEY, R.J., GEARY, T.W., ROBERTS, A.J. EFFECT OF HCG ADMINISTRATION APPROXIMATELY 5 D AFTER ARTIFICIAL INSEMINATION ON PROGESTERONE CONCENTRATIONS AND AI CONCEPTION RATES IN BEEF HEIFERS. JOURNAL OF ANIMAL SCIENCE SUPPLEMENT ABSTRACT #212. 2003. v. 81(Suppl. 1). p. 53. Technical Abstract: Objectives of this study were to determine if administration of hCG approximately 5 d after AI would increase plasma progesterone (P4) 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 MGA (0.5 mg/hd/d) for 14 d and an injection of PGF (Lutalyse; 25 mg; i.m.) 19 d later. Heifers were observed for estrus continuously during daylight from 0 to 4.5 d after PGF and bred by AI approximately 12 h after onset of estrus. Pregnancy status was determined by ultrasound approximately 50 d after AI. One-half of the heifers inseminated at Location 1 were randomly assigned to receive an injection of hCG (Chorulon, 3333 IU i.m.) 8 d after PGF and a blood sample was collected from all heifers 14 d after PGF for P4 analysis. One-half of the heifers inseminated at Location 2 were administered hCG on d 9 after PGF and a blood sample was collected from all heifers 17 d after PGF. Heifers at Location 1 had a 93% synchronization rate, exhibited estrus 2.46 ± .03 d after PGF and received hCG 5.05 ± .03 d after AI. Heifers at Location 2 had an 85% synchronization rate, exhibited estrus 2.69 ± .03 d after PGF and received hCG 5.8 ± .03 d after AI. Progesterone concentrations were greater (P < 0.01) for hCG treated heifers at both locations, 8.6 vs 4.6 ng/ml for treatment and control at Location 1 and 11.2 vs 5.6 ng/ml for treatment and control at Location 2. Conception rates (65 vs 70% for treatment and control, respectively) were not different (P = 0.36) at Location 1. Conception rates tended (P = 0.11) to be increased with hCG treatment at Location 2, 61 and 50% for treatment and control, respectively. In summary, hCG administration approximately 5 d after AI increased progesterone concentrations in beef heifers and tended to improve AI conception rates at one location.