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In Vitro Aging of Frozen Bull Semen¹

University of Illinois, Urbana 61801
Michigan State Universiry, East Lansing 48824

ABSTRACT

The change in fertility of bull semen with time in storage at –196 C was examined in data on inseminations by the Michigan Animal Breeders Cooperative over 5 yr. Intervals from collection to use were grouped by 10 days for the 1st yr, 30 days for the 2nd yr, 180 days for the 3rd yr, and a single class for semen stored 4 or 5 yr. There were 97,586 first inseminations from bulls with 10 or more ejaculates and from ejaculates with four or more classes. Nonreturn rates for 50-, 60-, 90-, and 180-day intervals post breeding were calculated. Heterogeneity of quadratic regressions of nonreturn rates on semen age was unimportant. Both regression and least squares analyses were used. Nonreturn rates increased to about 115 days of storage and remained there through the 4 and 5 yr age group. The lowest and highest nonreturn rates for a return interval differed by approximately 4%. Maximum differences in nonreturn rates for different intervals were at the lowest nonreturn rates.

¹ Supported in part by the Illinois and Michigan State Agricultural Experiment Stations.

² Animal Science Division, The University of Georgia, Athens 30602.