DEEP FREEZING OF BOAR SEMEN PACKAGED IN PLASTIC BAGS AND STRAWS

For practical reasons, a large volume (i.e. 5 ml) of frozen boar semen per insemination dose is desirable, but successful freezing has not been achieved, since optimal cooling rates have not yet been established. Post-thaw motility and the acrosome integrity of semen from four boars frozen with a programmable freezing machine, in mini-(0.25 ml), maxi-(5 ml) plastic straws and in 10 x 5 cm PVC- or Teflon(R) FEP-plastic bags (0.35-0.12 mm thick, 5 ml) was studied. The freezing of the semen was monitored using thermocouples placed in the straws and the bags. The freezing curve started from +5-degrees-C, at a rate of -3-degrees-C/min, to -6-degrees-C, it was held for 1 min at -6-degrees-C, and was followed by further drop to -100-degrees-C at a rate of -20-degrees-C/min, with subsequent storage in LN2. The bags had a much shorter freezing point plateau, compared to the maxi-straws. Post-thaw sperm motility was significantly higher when semen was frozen in mini-straws or in bags than in maxi-straws. The freezing procedure did not cause major acrosomal damages, significantly more normal apical ridges being present in the bags and mini-straws than in the maxi-straws. This in vitro evaluation indicates that the freezing method employed is satisfactory for freezing large volumes of boar semen into plastic bags.