The effect of freezer type, cryoprotectant, and processing methods on viability of frozen embryos

Two hundred forty excellent-quality blastocysts flushed from 53 superovulated Holstein heifers were frozen by 1 of 16 procedures in a 2 x 2 x 2 x 2 factorial design. The main effects included a simple, inexpensive, portable mechanical freezing unit instead of a programmable Liquid Nitrogen (LN) freezer for freezing bovine embryos, cryoprotective agents dimethyl sulfoxide (DMSO) and glycerol, addition rates of the cryoprotectants and freezing rates. Embryo viability was assessed morphologically and by fluorescein diacetate (FDA) evaluation. Neither the type of freezer, the cryoprotectant nor the rate of cryoprotectant addition affected embryo viability. Embryo survival after 12 h of incubation was higher (P < 0.05) using a conventional freezing rate than a two-step method (37.2 vs 16.5%). The correlation coefficient between viability evaluation methods (morphology vs FDA) was influenced by cryoprotectant and embryo processing methods and ranged from -0.13 to +0.70. This study indicates that more simplified embryo freezing equipment and handling procedures may provide protection equal to that of more complicated, expensive equipment and more time-consuming methods. Economical on-farm embryo freezing is feasible.