Effects of −196 and −76° C. Storage on the Resistance of Bull Sperm to Three Repeated Freeze-Thaw Treatments

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Abstract
To determine the effects of 3 repeated freeze-thaw treatments on spermatozoon survival at -196 and -76[degree]C, immediately after the initial freezing and after a 6-mo. storage period, a total of 30 ejaculates, 3 from each of 10 Holstein bulls, were employed. The number of progressively motile sperm per milliliter of extender during the immediate and 6-mo. freeze-thaw treatments (-196 and -76[degree]C) were significantly different (P < 0.01) among bulls, between refrigerants, and between storage periods. After a 6-mo. period, spermatozoa stored in liquid nitrogen exhibited greater resistance to repeated freeze-thaw treatments than paired samples in dry ice-alcohol. This resistance difference was not observed during the immediate freeze-thaw treatments. The percentages of sperm lost between repeated freeze-thaw treatments were significant within each temperature. Correlations of sperm survival, after each freeze-thaw treatment at -196 and -76[degree]C, with fertility of semen stored at-76[degree]C, were not statistically significant, range +0.17 to +0.48 on a bull basis.