Purpose: To investigate whether sterile filtered light paraffin oil (SPO) overlaying is superior to washed light mineral oil (WMO) in supporting the in vitro developmental competence of bovine follicular oocytes. In addition, the effects of the two types of oil overlaying were compared with oil overlaying plus co-culture (CC) on bovine embryo development in vitro.
Methods: Bovine follicular oocytes retrieved from abattoir-derived ovary were in vitro matured, fertilized and cultured in 50 microL drops overlayed with WMO or SPO and were subsequently evaluated for development rates. In second experiment, day 2 embryos grown under WMO overlaying were further cultured for 6 days in the presence (WMO+CC and SPO+CC) or absence of adult ear skin fibroblast-based co-culture system overlaid with WMO or SPO. Blastocysts from each group were evaluated for total nuclei number or were further cultured for 48 h to evaluate post-hatching development.
Results: SPO overlaying resulted in significant higher (p < 0.05) development rate to morula (44.8% versus 30.6%) and blastocyst (32.8% versus 21.7%) than WMO. Also, treatment of the day 2 embryo cultures with SPO overlaying or oil plus CC (WMO+CC or SPO+CC groups) reached significantly higher development rates from the morula stage compared to embryo cultures treated with the WMO overlaying (p < 0.05). However, the development rates of the SPO treatment group (morula: 72.7%; blastocyst: 53.1%) were slightly high compared to development of the culture treated with WMO+CC (69.6 and 50.4%, respectively). This similar developmental competence pattern was also observed in cell number and embryo hatching rate.
Conclusion: SPO overlaying is superior to WMO and WMO+CC in supporting in vitro development of bovine embryos. The development rates are further enhanced when embryos are cultured in co-culture system overlaid with SPO. Thus, these data suggest that overlaying oil can significantly influence the pre-implantation embryo development in vitro.