Effects of phenazine ethosulfate during culture of bovine embryos on pregnancy rate, prenatal and postnatal development

The objective was to evaluate the use of phenazine ethosulfate (PES) during culture of embryos on fetal and postnatal calf development. Oocytes collected from abbatoir-derived ovaries were matured and fertilized, and the resulting embryos were cultured in vitro by standard procedures, in a chemically defined medium plus BSA. Day 0 of culture was 18 ± 2 h after the onset of IVF. From 2.5 to 6.5 d, half of the eight-cell embryos served as controls, and the remainder were exposed to 0.3 μM PES, which decreases lipid content of embryos. Good-quality blastocysts exposed to PES (n = 38) or control (n = 35) blastocysts were transferred nonsurgically to synchronized recipients in estrus 6-7.5 d earlier, resulting in 9 calves in each group. These in vitro-produced pregnancies were evaluated weekly between 35 and 98 d postestrus by ultrasonography, and postnatal development of the calves was monitored for 1 month. Based on a limited number of transfers, use of PES during in vitro culture did not affect pregnancy rates compared to the control at 35 or 98 d (P > 0.1). Transfer at 7-7.5 d after estrus resulted in higher 98-d pregnancy rates than at 6-6.5 d (34% vs. 10%; P < 0.05). In vitro-derived fetuses that aborted had retarded fetal and placental development compared to those that went to term, but there was no difference in fetal loss between the PES treatment and controls. One calf in the PES group weighing 36 kg was born dead at 252 d of gestation, and another calf in this group was dead some hours after birth and weighed 22.2 kg when parturition was induced at 310 d of gestation. It is unclear whether these two abnormal calves were caused by the PES treatment, or were due to in vitro procedures in general. In conclusion, the use of PES during in vitro culture had no effect (P > 0.1) on pregnancy rates, conceptus losses between Days 35 and 98 of pregnancy, nor fetal postnatal development in calves born normally.