After sperm collection, pooled semen was diluted 1∶1 with Tselutin’s extender [17] at room temperature. Cooling was 20 min at 2°C, whereas in the last 2 minutes 6% DMA was added to the sample. Treated semen (25 µL) was directly dropped into the liquid nitrogen using a mechanical pipette (Eppendorf Multipette plus, Eppendorf Austria GmbH, Wien, Austria). Pellets were collected with forceps and put in cryo vials filled with LN, which were then stored in a container containing LN. Thus, inside the vials the pellets were also in LN. Thawing was done at 70°C for 10 sec in a self-fabricated automatic warming device. The content of the vials was poured into the preheated metal funnel of the device and the thawed sperm was collected into a glass vessel.