A new freezing box for the managing of semen cryopreservation process

Sperm freezing is of interest not only for animal breeding. The ability to use sperm in frozen form for AI is a key factor in ensuring the long-term preservation of genetic diversity through the creation of a sperm cryobank. The most widely used freezing method involves using straws as packaging sperm, then freezing them on liquid nitrogen (N2) vapor and finally immersing them in N2. The cryosurvival of sperm cells also varies among different animal species and has been correlated with the freezing rate, i.e., the distance of the straws above the N2 level. Identifying a freezing procedure that will report a fertilization rate as close as possible to that of fresh semen appears to be a challenge. Thus, there is a clear need to standardize the entire freezing process. In this research, a new device for semen cryopreservation is presented. The cryopreservation prototype allows management of the freezing rate by varying the heights of the support straws above the N2 level. A stainless steel box with a suitable floating frame equipped with a support for the straws was designed and fabricated. The holder is connected to the floating frame by means of two threaded rods that allow for height adjustment by screwing in appropriate guides. Two K-type thermocouples were used, one to measure the temperature of the nitrogen vapor at the height of the support and the other to measure the temperature of the semen inside the straw. In this way, different freezing protocols can be compared. By managing the freezing rate, the sperm freezing procedure, which is specific to animal species, could be standardized and thus variability in results could be minimized. In addition, improved cryosurvival and post-freezing sperm fertilization rates are expected.