Post-Thaw Survival of Bovine Spermatozoa Frozen by Different Methods in Buffered-Yolk and Skimmilk Extenders

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Abstract
Semen samples were extended in citrate-yolk-glycerol (CYG), Tris-yolk glycerol (TYG), and skimmilk-glycerol (SMG), frozen in a dry ice-alcohol bath and transferred to liquid N for storage at -196[degree]C. Glycerol levels (v/v) of 4.0, 5.6, and 7.2% in CYG, 6.4, 8.8, and 11.2% in TYG, and 9.0, 13.0, and 17.0% in SMG, the addition of 1.0% fructose, equilibration times of 1, 6, and 18 hr., freezing rates requiring 4, 8, 16, and 34 min., and storage for 1, 7, or 40 days were studied. The TYG extender consistently resulted in a higher percentage of sperm surviving freezing than did the CYG or SMG extenders (P < . 005). The optimum level of glycerol in TYG was about 8.8%, in CYG about 7.2%, and in SMG it was less than 9%. Fructose added to CYG and SMG was beneficial. Sperm motility did not decrease during storage at -196[degree]C. Bulls differed significantly (P < .005) and a large bull extender interaction was found. Many other statistically significant interactions (P < . 05) suggest that optimum conditions at one step in freezing are altered by changes in other steps.

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