|Funston, R - UNIV NEB LINCOLN|
|Olson, J - MT STATE UNIV BOZEMAN|
|Lipsey, R - AM SIMMENTAL ASSOC|
Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
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. WESTERN SECTION OF ANIMAL SCIENCE PROCEEDINGS. 2003. v. 54. p. 251-253. Interpretive Summary: Low levels of progesterone during maternal recognition of pregnancy may contribute to early embryonic losses. Increasing progesterone during this period may improve pregnancy rates in situations when exogenous factors may compromise pregnancy rates but may be of limited benefit when these factors are optimized.
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.