Effects of cooling ovaries before oocyte aspiration on meiotic competence of porcine oocytes and of exposing in vitro matured oocytes to ambient temperature on in vitro fertilization and development of the oocytes

Experiments were conducted to evaluate the effects of cooling porcine ovaries to low temperature (4 °C, 15 °C, 20 °C, 25 °C or 30 °C) for 1 h on the meiotic competence of their oocytes. Moreover, it was determined whether or not the exposure of in vitro matured oocytes to ambient temperature (20 °C, 25 °C or 30 °C) for 1 h affects the fertilization and developmental competence of the oocytes. There was no difference between the proportions of oocytes that underwent maturation to metaphase II when isolated from control ovaries held at 35 °C and ovaries exposed to 30 °C. However, the percentages of oocytes from ovaries exposed to 25 °C or less were significantly lower than those of oocytes from ovaries exposed to 30 °C and control ovaries. The proportions of total and normal fertilization of oocytes that had been exposed to 20 °C before in vitro fertilization (IVF) were significantly lower than those of control oocytes maintained at 38.5 °C. However, cooling in vitro matured oocytes had no effects on their cleavage and development to blastocysts after IVF. These data suggest that exposing porcine ovaries to a low temperature of 25 °C or less before aspiration of oocytes may adversely affect their subsequent in vitro maturation. It may be necessary to maintain the oocytes at a temperature of more than 25 °C during manipulation of oocytes for retaining the fertilizability of the oocytes.