Serum in embryo culture medium may be a potential cause of abnormal accumulation of lipid droplets, which is correlated to a higher sensitivity to cryopreservation. Moreover, serum may introduce pathogens. With the aim of developing a serum-free culture medium, we first (Experiment 1) investigated the effect of adding ITS (5 μg/mL insulin, 5 μg/mL transferrin, 5 ng/mL selenium) as a serum substitute in SOF medium on embryos cultured in large groups (20 embryos per culture drop of 20 μL) and we then (Experiment 2) analyzed the effect of adding BSA. In this second experiment, our serum-free culture media were also tested on embryos cultured in small numbers (5 embryos per drop of 20 μL) in order to mimic ovum pickup (OPU) conditions. Embryos were obtained from slaughterhouse oocytes, matured in vitro for 24 h in a serum-free enriched 199 medium (Donnay et al. 2004 Reprod. Fertil. Dev. 16, 274) containing ITS, and fertilized for 18 h. In experiment 1, embryos were cultured in SOF (Holm et al. 1999 Theriogenology 52, 683–700) supplemented with 0.1 mg/mL polyvinylpyrrolidane (PVP) without (SOF) or with ITS (SOF-ITS), or with 5% FCS (SOF-FCS). Cavitation occurred earlier in presence of serum (Table). Adding ITS to SOF increased blastocyst rates at Day 7 and Day 8 post-insemination (p.i.) and also the hatching rate. In experiment 2, embryos were cultured in SOF-FCS, SOF-ITS, or SOF-ITS supplemented with 4 mg/mL fatty acid free BSA (SOF-ITS-BSA). Within each condition, no differences were observed for blastocyst and hatching rates between embryos cultured in large or in small groups. Adding BSA to SOF-ITS increased blastocyst rate at Day 6 p.i. and also the hatching rate. At Days 7 and 8 p.i., blastocyst rates were higher in SOF-FCS than in SOF-ITS and tended to be higher than in SOF-ITS-BSA, especially for embryos cultured in small groups. Cell numbers of the resulting embryos were unaffected. These results indicate that: (1) ITS as supplement to SOF medium promotes embryo development in vitro. (2) BSA as protein supplement to SOF-ITS medium accelerates blastulation and improves hatching rate. (3) SOF-ITS and SOF-ITS-BSA are two serum-free culture media that can sustain development of embryos, also when cultured in small number, even though SOF-FCS tended to afford better rates of development. Further studies will include evaluation of other quality parameters including resistance to cryopreservation.
This work was supported by the Ministery of Agriculture of the Region wallonne de Belgique.
133 INSULIN, TRANSFERRIN AND SELENIUM WITH OR WITHOUT BSA IN A SERUM-FREE CULTURE SYSTEM FOR BOVINE EMBRYO, AND ITS SUITABILITY FOR EMBRYOS CULTURED IN SMALL GROUPS
