A SERUM-FREE MEDIUM FOR USE IN A CUMULUS CELL COCULTURE SYSTEM FOR BOVINE EMBRYOS DERIVED FROM IN-VITRO MATURATION AND IN-VITRO FERTILIZATION

The objective of this study was to develop a serum-free medium for the co-culture of bovine embryos that would yield a percentage of blastoc ysts equal to that obtained with fetal bovine serum (FBS)-supplemented medium. Cumulus cell-enclosed oocytes (CEO) matured and inseminated i n vitro were cultured in a tissue culture medium (TCM)-199 or in a ser um-free medium (bovine embryo culture medium; BECM) until 240 h post i nsemination. Replacement of 10% (v/v) FBS with either 3 mg crystallize d bovine serum albumin (BSA)/ml or 3 mg fatty acid-free BSA/ml in TCM- 199 had no effect (P>0.14) on embryo development to the greater than o r equal to 2-cell (51 to 60%), greater than or equal to 8-cell (24 to 33%), blastocyst (16 to 19%) and hatched-blastocyst (7 to 10%) stages at 48, 96, 192 and 240 h post insemination, respectively. Oocyte-enclo sing cumulus cells in BSA-supplemented medium grew in clusters rather than in layers, as was noted in FBS-supplemented medium. When CEO were cultured in fatty acid-free BSA-supplemented media (TCM-199 and BECM) , a significantly (P<0.001) higher percentage of oocytes developed to blastocysts after culture with (22%) or without (18%) a cumulus cell m onolayer than after denuding the oocytes (7%). Glucose in concentratio ns of 0 to 5.56 mM added for periods of 18 and 120 h post-insemination had neither a stimulatory nor a deleterious effect on preimplantation development. In conclusion, a serum-free medium supplemented with BSA can be successfully used in a cumulus cell co-culture system for bovi ne embryos.