Abstract
In Japan, most domestic cattle are produced by artificial insemination using cryopreserved semen. Basic
principles and protocols for cattle semen freezing have not been changed for more than 50 years. Recently,
however, the improvement of semen cryopreservation has been required because of low conception and/or
effective use of sex-selected sperm in dairy cows. In cattle embryos, a type of slow-freezing called “Direct
method”, in which cryopreserved embryos in a straw can be transferred into a recipient directly, has been
commonly used for in vivo fertilized embryos. However, low survival rates were obtained in in vitro fertilized
embryos and in biopsied embryos. Vitrification has not been popular in the cryopreservation of cattle embryos
because cryopreserved embryos are needed to be loaded into a straw for embryo transfer after warming. More
simple and practical methods with higher efficiency are needed in the cryopreservation of cattle sperm and
embryos.
