Currently in the pig industry, embryo transfer programs involve the transport and transfer of freshly collected embryos, because the efficiency of embryo transfer using cryopreserved embryos is still unacceptably low. The current conditions used to transport pig embryos have been shown to reduce their developmental potential¹. The aim of this study was to determine the effect of the media pH buffer components, Hepes and Mops, on the maintenance of pig embryo viability during extended out-of-incubator culture.

In experiment 1, Day 4 in vitro produced pig embryos were loaded in 1ml transfer syringes containing modified Porcine Zygote Medium-3 (PZM-3)² buffered with either 10mM Hepes, 10mM Mops, 5mM Hepes/5mM Mops, or 10mM Hepes/10mM Mops and held at 38.5°C in air for 3h. In experiment 2, embryos were loaded in 1ml or 5ml transfer syringes containing 5mM Hepes/5mM Mops buffered PZM-3 and held at 38.5°C in air for 3 or 24h. Following out-of-incubator culture, the embryos were returned to bicarbonate-buffered PZM-3 in 6% CO₂, 5% O₂ and 89% N₂. Control embryos were cultured in bicarbonate-buffered PZM-3 for the entire duration. Data were subjected to ANOVA and Tukey’s test when differences were found.

The blastocyst formation rate of embryos exposed to 5mM Hepes/5mM Mops (13%) was similar to that of control embryos (12%), and greater than the rates for embryos exposed to the other buffer compositions examined (5-6%; P<0.05). Even after the 24h out-of-incubator culture, the blastocyst formation rates of embryos exposed to 5mM Hepes/5mM Mops did not differ significantly from that of the control embryos.

These findings have important implications for the pig industry, as the ability to transport freshly collected embryos for 24 h without significant loss of viability would greatly enhance the use of embryo transfer in genetic improvement programs.

LK Bartolac was supported by a Pork CRC Honours award.