291 VARIOUS FACTORS INFLUENCING PREGNANCY RATES AND CALVING CHARACTERISTICS FOLLOWING TRANSFER OF OPU-IVP EMBRYOS PRODUCED IN A COMMERCIAL SYSTEM

Abstract

OPU-IVP is nowadays an assisted reproduction technique in which output for each step is variable. The aim of this work was to identify factors influencing calving rate and calf characteristics through a retrospective study conducted from 356 OPU sessions and 137 pregnancies on a farm. Donor females were stimulated with FSH in five decreasing doses (400 ¼g for cows and 250 ¼g for heifers). Collected oocytes were matured for 24 h in M199 plus fetal calf serum, FSH, epidermal growth factor (EGF), and estradiol. They were then fertilized in TALP with frozen-thawed semen and zygotes were cultured for 6 days on Vero cell monolayers in B2 medium. Embryos were transferred as fresh to recipients on Day 7; 137 pregnancies were followed up to calving. Gestation length, calving conditions and calf characteristics (sex and birth weight assessed by farmers) were recorded and compared to national standards (UPRAs data). The mean number of collected oocytes per session was 14; 11.6 were selected for IVM, 8.5 cleaved, and 3.9 developed to the blastocyst stage (40.4% of the embryos were Grade 1, 35.3% G2, and 20.5% G3). On average, 2.9 embryos were transferred into recipients, leading to an average of 1.6 pregnancies on Day 35 and 1.4 on Day 90 (76% of recipients were heifers). Pregnancy rates were higher in heifers than in cows (54.5% vs. 47.8%; P < 0.05). Pregnancies led to birth of a healthy calf in 81.9% of the OPU sessions (1.1 per session), the 18.1% losses being divided between 4.4% abortion (n = 6) and 13.7% perinatal mortality (n = 18). Gestation length from IVF pregnancies was longer than in national breeds standards (trial = 291 vs. national = 287 days). Moreover, 10% of calvings were induced. Calving conditions were mainly dependent on age of recipients: 70% of the heifers were assisted compared to 40.9% of the cows. No effect of gestation length or sex of calf was observed on calving difficulties. Sex ratio did not deviate in calves produced by OPU-IVF (52.3% of males and 47.7% of females). However, it was influenced by embryo quality, with the proportion of males decreasing from 56.3% to 44.4% for G1 to G3 embryos. The mean weight of healthy calves issued from IVP embryos averaged 47.1 kg ± 10.1 and was not significantly higher than the national breed standards. The deviation (kg) from national breeds standards ranged from -20 kg to 0 in 68.8% (n = 90), from 1 to 15 kg in 16.0% (n = 29), and greater than 15 kg in 9.2% (n = 12) of the calves. Even if the mean deviation was not significant, those 12 calves in the >15 kg group should be considered as large. However, they were issued from two different donor females, so that this effect could also be attributed to a mother effect. To conclude, the effect of recipient parity on pregnancy rates was confirmed. The OPU-IVP system used in this trial did not seem to influence significantly sex ratio and weight of calves. Further studies are needed to investigate the sources of variation of gestation length.