200 Improving efficiency of embryo transfer (ET) programs by optimizing fertility and management of recipients
Abstract Multiple experiments were performed to optimize efficiency and fertility in recipients of fresh in vitro produced (IVP) embryos. In experiment 1, heifers (n = 520) were synchronized and received an embryo on d 6–8 after estrus or 6–8 d after GnRH in a fixed time ET (FTET) program using modified 5-d CIDR-Synch protocol (d-8: CIDR inserted; d-3: CIDR removed and PGF2α treatment; d-2: second PGF2α; d0: GnRH to induce ovulation). Pregnancy per ET (P/ET) at d 32 and d 60 were similar but pregnancy per treated potential recipient (efficiency of recipient utilization) was greater for FTET than estrus (+49.7%). Subsequent experiments sought to optimize FTET protocol by analyzing whether CIDRs could be used multiple times (up to 4 uses similar P/ET) and whether multiple PGF2α treatments were needed at end of program (no difference when no GnRH given at start of protocol). Thus, a simple, inexpensive FTET program has similar fertility as ET after estrus but is more efficient at recipient utilization. A large retrospective analysis (n = 12,569 ET) was performed using FTET program. Embryo stage and quality were major embryo factors impacting P/ET. Transfer of d 7 fresh embryo to d 7 or d 8 recipient was better than d 6 (+24.4%). Two experiments (GnRH or CIDR treatment) evaluated increasing circulating P4. In GnRH experiment, heifers (n = 1,562) on d5 received GnRH (200 μg) or Control (untreated). On D12, P4 was greater (P < 0.001) in GnRH-treated (7.2 ± 0.1ng/ml) vs Controls (6.0 ± 0.1ng/ml). There was greater P/ET at D33 and D60 of pregnancy for Stage 7 than 6 embryos. Treatment with GnRH did not alter P/ET but decreased pregnancy loss between D33 and D60 in heifers receiving Stage 7 embryos (11.6 vs 27.6% in recipients with accessory CL on d 33). In CIDR experiment, treatment with 2 CIDRs (from d 13; one new CIDR each 7 d) elevated circulating P4 and tended to decrease pregnancy loss (d 27 to 62; 25.9 vs 11.9%) and increase P/ET (40.4 vs 53.6% on d 62). Thus, elevating P4 decreased pregnancy loss during FTET program using fresh IVP embryos.