Preservation of Bovine Spermatozoa at −79 and −196° C

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Abstract
Studies were conducted to determine the effect of storage temperatures of -79 and -196[degree]C on fertility of bovine spermatozoa. Semen in 145 ejaculates from 43 bulls was frozen in an egg yolk-citrate extender and divided for storage at -79 and -196[degree]C. The weighted mean difference, in 60- to 90-day non-return (NR) rate, of 2.9% was statistically significant (P<0.02) in favor of storage at -196[degree]C. Breeding efficiencies obtained on second-service inseminations from the 2 storage temperatures showed a 1.1% NR in favor of liquid nitrogen (LN) storage. However, the difference was not statistically significant (P = 0.05). In a 2d trial semen was frozen in LN to -80[degree]C, then divided for storage at -79 and -196[degree]C. On a limited number of services a weighted mean difference of 5.3% was obtained in favor of LN. The difference approached significance (P<0.20). Combined data on a total of 9742 first-service inseminations including both storage temperatures showed a 60- to 90-day NR of 71.1 and 68.4% for liquid nitrogen and dry ice-alcohol storage, respectively. The difference was significant (P < 0.02). Criteria collected on 132 ejaculates and correlated with fertility showed some significant correlations, but all correlations obtained were too low to be useful in predicting the fertility of frozen semen.