REMOVAL OF CYTOPLASMIC LIPID ENHANCES THE TOLERANCE OF PORCINE EMBRYOS TO CHILLING

The lipid content of porcine 1-cell stage embryos was reduced (delipated) through the use of micromanipulation to remove the lipid layer formed after centrifugation. Of 94 delipated embryos chilled to 4 degrees C for 1 h at the 1-cell or 2- to 4-cell stage, 60 (64%) cleaved in culture with development to the morula-blastocyst stage, whereas all of the control embryos lysed within 24 h. Significantly more embryos developed beyond the 8-cell stage when they were chilled at the 2- to 4-cell stage compared with chilling at the 1-cell stage (44%, 20 of 45 vs. 18%, 9 of 49). Fewer embryos developed after chilling if they were only partially rather than fully delipated. Developmental rates of partially delipated embryos to the 8-cell and blastocyst stages were 33% (13 of 40) and 8% (3 of 40), rates significantly (P < 0.001 and 0.05) lower than the rate for fully delipated embryos (73%, 38 of 52 and 27%, 14 of 52, respectively). The in vitro developmental competence of the unchilled fully delipated embryos was comparable to that of intact zygotes (cleavage: 94%, 45 of 48 vs. 87%, 26 of 30; greater than or equal to blastocyst: 40%, 13 of 48 vs. 57%, 17 of 30). These data demonstrate that the sensitivity of porcine embryos to chilling is related to their high lipid content and that they can become tolerant to chilling if their lipid content is reduced.