Synthetic oviductal fluid and oviductal cell coculture for canine oocyte maturation in vitro

The perfection of in vitro maturation in the bitch has yet to be achieved, and is an essential prerequisite for gamete salvage programmes in endangered canine species. In contrast to most mammals, the bitch ovulates an immature oocyte which undergoes meiotic maturation within the oviduct. A model of the oviductal environment may therefore be useful for performing in vitro maturation. This study was performed to investigate the effect of introducing an oviductal element to the culture environment, first with the use of a synthetic oviductal fluid (SOF), and secondly, using coculture with isolated canine oviductal epithelial cells, upon the rate of oocyte maturation in vitro. It was found that there was no difference in the proportion of oocytes undergoing germinal vesicle breakdown (GVBD) after 48 h in culture between SOF containing 0.3% bovine serum albumin (BSA, 45%), containing 4% BSA (36%) and control medium 199 (27%). There was also no difference in oocyte nuclear maturation to metaphase I/anaphase I/metaphase II (MI/AI/MII) after 48 h in culture between SOF containing 0.3% BSA (5%), containing 4% BSA (7%) and control medium 199 (6%). In addition, there was no difference in oocyte nuclear maturation to MI/AI/MII after 96 h between SOF containing 0.3% BSA (0), containing 4% BSA (7%) and control medium 199 (11%). In contrast, the proportion of oocytes undergoing GVBD after 96 h in culture was affected by the treatment used, with 27% in SOF+0.3% BSA, 62% in SOF+4% BSA and 63% in medium 199. It was found that there was no difference in the proportion of oocytes undergoing GVBD between the coculture treatments 199 (33%), 199+cells (37%), coculture medium (30%) and coculture medium+cells (49%), and for oocyte nuclear maturation to MI/AI/MII, between medium 199 (2%), 199+cells (0), coculture medium (6%) and coculture medium+cells (2%) after 48 h in culture. In addition, there was no difference in oocyte nuclear maturation to GVBD after 96 h between 199 (61%), 199+cells (59%), coculture medium (65%) and coculture medium+cells (53%). In contrast, the proportion of oocytes maturing to MI/AI/MII after 96 h in culture was affected by the treatment used, with a significant difference between 199 (0), 199+cells (9%), coculture medium (0) and coculture medium+cells (0). It was shown, therefore, that the culture of oocytes in the SOF improved oocyte nuclear maturation when supplemented with a high concentration of protein and that culture in the presence of oviductal epithelial cells improved oocyte maturation, but only after a prolonged period of time.