[Freezing of sperm distributed in IMV pipettes and aluminum tubes over nitrogen vapors]

The freezing is described of the dense fraction of boar semen as diluted with the Serdika medium at 1:2 ratio and alloted into IMV 5 cm3 tubes and aluminum 8 cm3 tubes. The check variant made use of semen samples frozen in the form of granules over dry carbon dioxide. Both types of tubes were frozen over nitrogen vapours at initial temperatures of -90 degrees C, -100 degrees C, -110 degrees C, -120 degrees C, -130 degrees C, and -140 degrees C for 15 min and stored in nitrogen for 48 h. The semen was thawed in water bath at 55 degrees C. It was found that the dense fraction of ejaculates of good quality that had cryotolerance in diluted state was best frozen at -140 degrees C, and -130 degrees C. The regimes of freezing at such temperatures were characterized by a higher speed in the first 5 min (from 18.4 degrees C to 12.0 degrees C per minute for IMV tubes, and from 14.8 degrees C to 9.4 degrees C for aluminum tubes), with slowing down in the following 10 minutes.