Silicone oil used in microdrop culture can affect bovine embryonic development and freezability

The effect of silicone and paraffin oil, which is routinely used to overlay in vitro embryo culture media, on bovine in vitro embryonic development an d on their subsequent survival after one-step vitrification was investigate d. In experiment 1, silicone oil batch 13 was compared with paraffin oil. E mbryonic development to the eight-cell and blastocyst stage was significant ly impaired by silicone oil batch 13 in comparison with paraffin oil (p < 0 .0001). Normal looking blastocysts produced under both types of oil were vi trified. None of the blastocysts that were produced under silicone oil batc h 13 survived the vitrification procedure whereas 59% of the blastocysts su rvived when they were cultured under paraffin oil both before vitrification and after warming. In experiment 2, another batch no. 7 of the same brand of silicone oil was compared with paraffin oil. No effect of the type of oi l on embryonic development until the eight-cell stage could be demonstrated . However, the blastocyst formation rate was significantly lower with silic one oil batch 7 than with paraffin oil. The survival of vitrified blastocys ts after warming was significantly improved when silicone batch 13 was repl aced by batch 7 (0 and 41%, respectively) although it was still lower when compared with the survival of blastocysts developed under paraffin oil (53% ) (p < 0.05). In further attempts to find the cause of the problem, the sil icone and paraffin oils were analysed for Zn-contents (experiment 3). Zn-co ntents were comparable for silicone oil batch 13 (0.87 muM), silicone oil b atch 7 (0.62 muM) and paraffin oil (0.73 muM). Media, conditioned by bovine oviduct epithelial cells cultured with a silicone or paraffin oil overlay were analysed by means of thin layer chromatography for differences in qual itative fatty acid composition. It was possible to detect that oil overlay changed the relative abundance of fatty acids in the different lipid classe s. In the free fatty acid fraction, it was skewed in favour of palmitic aci d and in cholesterol esters and phospholipids in favour of linoleic acid. I t appears that due to the changed lipid contents of the medium, embryonic m embranes are rendered more susceptible to freezing due to altered membrane composition or by membrane damage caused by lipid peroxidation.