|Funston, R - U OF NEBRASKA NORTH PLATT|
|Lipsey, R - AM.SIMMENTAL ASSOCIATION|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 10, 2005
Publication Date: June 1, 2005
Citation: Funston, R.N., Lipsey, R.J., Geary, T.W., Roberts, A.J. 2005. Effect of administration of human chorionic gonadotropin after artificial insemination on concentrations of progesterone and conception rates in beef heifers. Journal of Animal Science. 83:1403-1405. Interpretive Summary: Early embryonic mortality may be as high as 30% with a majority of losses occurring between d 8 and 16 of gestation, resulting in lengthened post-partum interval, later born calves and decreased opportunities for females to become pregnant during a limited breeding season. Low progesterone concentrations during early pregnancy may negatively impact embryonic development and maternal recognition of pregnancy. Thus, several strategies have been used to increase progesterone concentration after breeding, including the administration of the hormone hCG during the early luteal phase, which induces ovulation and results in formation of an accessory CL. The most dramatic effects of hCG administration on conception rates have been observed in dairy herds of low fertility. Our objective was to evaluate effects of administering hCG to beef heifers approximately 5-6 d after AI on plasma concentrations of progesterone and conception rates. Results indicate that while hCG increased circulating concentrations of progesterone, conception rates were only improved in 1 of 3 herds evaluated.
Technical Abstract: The objective of this study was to determine if 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 MGA (0.5 mg'hd-1'd-1) for 14 d and an injection of PGF2' (Lutalyse, 25 mg i.m.) 19 d later. Heifers were observed for estrus continuously during daylight from 0 to 4.5 d after PGF2' and bred by AI approximately 12 h after onset of estrus. 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 PGF2' and a blood sample was collected from all heifers 14 d after PGF2' for progesterone analysis. One-half of the heifers inseminated at Location 2 were administered hCG on d 9 after PGF2' and a blood sample was collected from all heifers 17 d after PGF2'. Heifers at Location 1 had a 93% synchronization rate, exhibited estrus 2.46 ' 0.03 d after PGF2' and received hCG 5.05 ' 0.03 d after AI. Heifers at Location 2 had an 85% synchronization rate, exhibited estrus 2.69 ' 0.03 d after PGF2' and received hCG 5.8 ' 0.03 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. Pregnancy status was determined by ultrasound approximately 50 d after AI. Conception rates (65 vs 70% for treatment and control, respectively) were not different (P = 0.36) at Location 1. Conception rates tended (P < 0.10) to be increased with hCG treatment at Location 2 (61 vs. 50% for treatment and control, respectively). In summary, hCG administration approximately 5 d after AI increased concentrations of progesterone in beef heifers and tended to improve AI conception rates at one location.