110 TREATMENT WITH GnRH ON DAY 5 REDUCES PREGNANCY LOSS IN HEIFERS RECEIVING IN VITRO-PRODUCED EXPANDED BLASTOCYSTS

Abstract

The hypothesis was that GnRH on Day 5 of a synchronized cycle in embryo transfer recipients would increase progesterone (P4) concentrations, embryo size, and fertility. Holstein and cross-bred Holstein heifers (n = 1562) were synchronized using a modified 5-day CIDR Co-Synch as follows: Day –8 CIDR inserted; Day –3 CIDR removed; prostaglandin F2α treatment; Day –2 second prostaglandin F2α; Day 0 gonadotropin-releasing hormone (G1, 100 μg of gonadorelin acetate) to induce ovulation. On Day 5.5, heifers were assigned in a completely randomised design to 1 of 2 treatments: Control (untreated) or GnRH (200 μg of gonadorelin acetate). Transfer of fresh in vitro-produced embryos was performed between d 6 and 8 after G1. Data collected from each heifer included embryo stage and quality, body condition score, technician, interval from G1 to transfer, and number of previous transfers. All heifers were evaluated by transrectal ultrasonography on Day 5, 33, and 62 and a subset of heifers was scanned on Day 12 (n = 718; to determine ovulation to treatment) and another subset on Day 33 (n = 296; 16-s video to determine embryo and amniotic vesicle size). Serum P4 was determined from a subset of heifers on Day 12 (n = 467). Fertility data were analysed by logistic regression (LOGISTIC procedure, SAS 9.4), whereas continuous outcomes were analysed by ANOVA (MIXED procedure). Ovulation to Day 5.5 gonadotropin-releasing hormone was 83.9% (302/360) in GnRH-treated heifers v. 3.3% (12/358) in Control (P < 0.001). Progesterone on Day 12 was greater in GnRH-treated heifers 7.2 ± 0.1 ng mL–1 v. Controls 6.0 ± 0.1 ng mL–1 (P < 0.001). There was an effect of embryo stage at Day 33 and 60 of pregnancy, with Stage 7 having greater P/ET than Stage 6 embryos. Treatment with GnRH did not alter pregnancy per embryo transfer with either embryo stage but decreased pregnancy loss in Stage 7 embryos, as shown in Table 1. Embryo size measured as crown-rump length (CRL) did not differ, as shown in Table 1. Similarly, amniotic vesicle volume (AVV) was not different between GnRH (549.1 ± 16 mm3) and Control (543.5 ± 14 mm3; P = 0.86), nor was there an interaction between treatment and embryo stage (P = 0.71). In addition, neither AVV (P = 0.22) nor CRL (P = 0.41) were associated with pregnancy loss between Day 33 and 60. In conclusion, treatment with GnRH on Day 5 resulted in increased P4 and a reduction in pregnancy loss in heifers receiving a Stage 7 embryo without changing conceptus size. Table 1.Pregnancies per embryo transfer (P/ET), crown-rump length (CRL), and pregnancy loss in embryo recipients receiving gonadotropin-releasing hormone (GnRH) on Day 5.5 v. control