Comparison of cryoprotectants and methods of cryopreservation of fowl spermatozoa.

The deleterious effects of three cryoprotectants, glycerol, dimethylsulfoxide (DMSO), and dimethylacetamide (DMA), were compared on fowl spermatozoa. The viability and integrity of spermatozoa were measured with eosin-nigrosin smears. Glycerol was the least deleterious cryoprotectant, followed by DMA, and DMSO was the most toxic. Methods employing either glycerol or DMA were then compared for the cryopreservation of semen in either straws or pellets. Fertility was measured following artificial insemination. The highest fertility rates were obtained with semen frozen with DMA in pellets directly plunged in liquid nitrogen, DMA being added at -6 C (92.7%) or 5 C (84.7%). When semen was frozen in straws, glycerol equilibrated for 1 or 30 min gave the highest fertility results, but the fertility rates were lower (53.7 and 63.9%) than with DMA in pellets. The lowest results (26.7%) were obtained when semen was frozen in straws with DMA. When semen was frozen in pellets at very high cooling rates, DMA was superior to glycerol as a cryoprotectant, as evidenced by fertility. In contrast, when straws and low freezing rates were used, glycerol gave better results; however these results were never as high as those obtained with DMA and pellets. In conclusion, under our experimental conditions, the highest fertility rates were achieved with DMA and pellets. However, for gene banking, which requires high levels of safety and clear identification, glycerol and straws are more convenient.