Effect of the cryopreservation method used, the embryonic stage and the use of conjugated linoleic acid isomers on the cryotolerance of in vitro-produced bovine embryos

Abstract

<p>Conjugated linoleic acid (CLA) might be able to improve the cryotolerance of <em>in vitro-</em>produced (IVP) embryos. The effect of two CLA isomers on the cryotolerance of bovine IVP embryos, as well as that of the stage of embryonic development and the method used for cryopreservation was evaluated by three experiments. In Experiment 1, oocytes (n = 3,917) were fertilized <em>in vitro </em>and cultured with 0, 50, 100, or 200 ?M <em>trans-</em>10<em>, cis-</em>12 (t10, c12 CLA). In Experiment 2, fertilized oocytes (n = 2,131) were cultured with 100 ?M t10, c12 or <em>cis-</em>9<em>, trans-</em>11 (c9<em>, </em>t11 CLA), or a combination of both isomers. The embryos were vitrified at the blastocyst (BL) or the expanded blastocyst (EB) stage. In Experiment 3, oocytes (n = 1,720) were fertilized and cultured with or without 100 ?M t10, c12 CLA, and the blastocysts were vitrified or frozen. Blastocyst development rate as well as the rates of re-expansion and hatching after thawing was recorded. Moreover, the mean cell number and mRNA expression of acetyl-CoA carboxylase (ACC1) and stearoyl-CoA desaturase (SCD1) as well as fatty acid synthase (FASN) multienzyme complex were determined. In Experiment 1, the highest concentration of t10, c12 CLA that did not reduce blastocyst development rate was 100 ?M. In Experiment 2, the rates of re-expansion and hatching among the EBs obtained through IVP after supplementation with t10, c12 CLA (73.1% and 57.7%), with c9, t11 CLA (80.0% and 68.6%), with the combination (78.3% and 52.2%), and with the control group (85.4% and 58.3%) were similar. At the BL stage, the rates of re-expansion and hatching were lower than those at the EB stage, and CLA combination allowed a hatching rate (8.0%) lower than that observed in the control group (40.0%). In Experiment 3, the hatching rates for vitrified EBs (vitrified control; 67.4%) and vitrified CLA EBs (65.8%) were higher than those obtained for frozen EBs, exposed (13.3%) or not exposed (28.6%) to CLA. In addition, in Experiment 3, the hatching rate was higher at the EB stage in vitrified groups, while the rates of BL and EB were similar in frozen groups, thus proving that vitrification was more efficient than freezing for IVP bovine embryos. In Experiment 3, CLA isomer t10, C12 did not influence the embryonic cell number or mRNA expression of ACC1 and SCD1 enzymes, but decreased the mRNA expression of FASN. In conclusion, 100 ?M CLA did not affect subsequent embryonic development. However, neither CLA isomer improved the cryotolerance of IVP bovine embryos.</p>