Bovine in vitro embryo production and oocyte preservation

• Main Author: Giritharan, Gnanaratnam
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/10246

Several experiments were done with the overall objective to improve the production of in vitro embryos. In the first experiment, the optimum period for ovary removal and the effect of FSH priming at standing estrus were investigated to maximize viable oocyte yield from culled cows. Animals were ovariectomized either 2 d after induced estrus, 2 d after a single dose of FSH on the day of standing estrus or randomly irrespective of the stage of the estrous cycle. Oocyte recovery and, cleavage and blastocyst formation rates were recorded for each treatment. Highest oocyte recovery was obtained from FSH-primed cows. Cleavage and blastocyst formation rates were not significantly different among treatments. These results indicated that FSH treatment increases oocyte yield in culled cows. The second experiment examined methods for the short-term preservation of bovine oocytes. Oocytes were matured in either i) straws containing maturation media (MM) at 38.5 °C without 5% C02, ii) straws containing MM at room temperature without 5% C02 or iii) culture plates containing MM at 38.5 °C and 5% C02. After 24 h, oocytes were fertilized and cultured in vitro. Oocytes, which were matured at room temperature without 5% C02, showed significantly lower maturation, fertilization, cleavage, and blastocyst formation rates than those matured at 38.5 °C. Oocytes matured at 38.5 °C with or without 5% C02 showed similar maturation, fertilization and cleavage rates, however, those with 5% C02 showed a significantly higher blastocyst formation rate. Therefore, 38.5 °C and a 5% C02 environment are optimal for oocyte maturation and embryo development. The third experiment was done to find a suitable cryopreservation method for the long-term preservation of bovine oocytes. Developmental competency of immature and mature oocytes undergoing slow freezing or vitrification was measured by cleavage and blastocyst formation rates. None of the slow frozen mature oocytes or vitrified immature and mature oocytes cleaved 72 h after insemination or developed to the blastocyst stage. Although some slow frozen immature oocytes eventually cleaved, the cleavage rate was significantly lower than that of control oocytes. This indicated that both cryoprotectant and cooling procedure affect the developmental competency of bovine oocytes. [Scientific formulae used in this abstract could not be reproduced.]