Effect of Treatment with Human Chorionic Gonadotropin (hCG) on Day 7 of the Estrous Cycle on Pregnancy Outcomes and Pregnancy Losses in Holstein Dairy Heifers Receiving Artificial Insemination or IVF Embryo Transfer

Our objective was to assess the effect of treatment with human chorionic gonadotropin (hCG) on day 7 of the estrous cycle on progesterone (P4), pregnancy-specific protein B (PSPB), pregnancies per AI (P/AI) or pregnancies per embryo transfer (P/ET) and pregnancy loss in nulliparous Holstein dairy heifers. Heifers in Experiment 1 were randomly assigned to receive no treatment (control, C; n=129) or 2,000 IU hCG 7 d after AI after detected estrus (hCG, n=132). Heifers in Experiment 2 were randomly assigned to receive no treatment (control, C; n=143) or 2,000 IU hCG (hCG, n=148) at transfer of an IVF embryo 7 d after a synchronized ovulation. Blood samples were collected from a subgroup of heifers in each experiment (Experiment 1, n=82; Experiment 2, n=104) at 7, 11, 18, 20, 25, 28, and 32 d after estrus or ovulation for all heifers and at d 35, 39, 46, 53, 60, and 67 for pregnant heifers. Blood samples were assayed for P4 by RIA and for PSPB by ELISA. Data were analyzed by ANOVA and logistic regression using the MIXED and GLIMMIX procedures of SAS. For Experiment 1, treatment with hCG increased (P<0.01) P4 concentrations from 11 to 32 d after AI (13.2 vs. 8.6 ng/mL); however, P/AI at 32 and 67 d after AI did not differ (P=0.73 and 0.98, respectively) between treatments (43% vs. 41%; and 41% vs. 41%, for C vs. hCG heifers, respectively). Treatment did not affect (P=0.47) PSPB concentrations from 11 to 67 d of pregnancy (2.1 vs. 2.3 ng/mL for C vs. hCG heifers, respectively). For Experiment 2, treatment with hCG increased (P<0.01) P4 concentrations from 11 to 32 d after ovulation (11.5 vs. 7.1 ng/mL). Although P/ET at 32 d after ovulation did not differ (P=0.39) between treatments (43% vs. 48% for hCG vs. C heifers, respectively), hCG heifers had fewer (P=0.05) pregnancy losses from 32 to 67 d after ovulation than C heifers (10% vs. 22%). Treatment did not affect PSPB (P=0.72) concentrations from 11 to 67 d of pregnancy (2.3 vs. 2.4 ng/mL for C vs. hCG heifers, respectively). We conclude that treatment with 2,000 IU hCG on d 7 of the estrous cycle increased P4 concentrations but did not affect P/AI or P/ET 32 d after estrus or ovulation in both experiments and decreased pregnancy loss only for heifers receiving IVF embryos. Supported by USDA NIFA Hatch project 1006519