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 and on their subsequent survival after one-step vitrification was investigated. In experiment 1, silicone oil batch 13 was compared with paraffin oil. Embryonic development to the eight-cell and blastocyst stage was significantly impaired by silicone oil batch 13 in comparison with paraffin oil (p < 0.0001). Normal looking blastocysts produced under both types of oil were vitrified. None of the blastocysts that were produced under silicone oil batch 13 survived the vitrification procedure whereas 59% of the blastocysts survived 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 oil on embryonic development until the eight-cell stage could be demonstrated. However, the blastocyst formation rate was significantly lower with silicone oil batch 7 than with paraffin oil. The survival of vitrified blastocysts after warming was significantly improved when silicone batch 13 was replaced 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 silicone and paraffin oils were analysed for Zn-contents (experiment 3). Zn-contents were comparable for silicone oil batch 13 (0.87 microM), silicone oil batch 7 (0.62 microM) and paraffin oil (0.73 microM). 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 qualitative fatty acid composition. It was possible to detect that oil overlay changed the relative abundance of fatty acids in the different lipid classes. In the free fatty acid fraction, it was skewed in favour of palmitic acid and in cholesterol esters and phospholipids in favour of linoleic acid. It appears that due to the changed lipid contents of the medium, embryonic membranes are rendered more susceptible to freezing due to altered membrane composition or by membrane damage caused by lipid peroxidation.