Cryopreservation by vitrification of in vitro obtained bovine oocytes and embryos

Cryopreservation refers to the preservation of biological material at low temperatures. It applies to various types of somatic cells, tissues, and organs, but also to germplasm, sperm, ova, ovaries, embryos, etc. There are two methods of cryopreservation – slow freezing and vitrification. After the concept of minimum volume cooling (MVC) was developed, vitrification became popular. This approach is based on the small sample volume, which leads to ultra–fast freezing, i. e. extremely high rates of cooling and warming. As determining factors for the achievement of vitrification, the speed of cooling/heating and viscosity of the sample are indicated. Nowadays, there is a tendency to reduce or even stop using cryoprotectants by increasing the cooling/warming rate. In many cases, fetal calf serum, albumin, or other substances containing high molecular weight proteins are added to the cryopreservation media.