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Variance Components of Semen Criteria from Bulls Ejaculated Frequently and Their Use in Experimental Design

Department of Animal Science, Cornell University, Ithaca, New York 14850

ABSTRACT

Variance components for 16 characteristics of bull semen were computed from 1,536 ejaculates from 63 Holstein bulls ejaculated four times per week. Based on animal and error components of variance, number of bulls and ejaculates per bull required to detect treatment differences for two treatment experiments under specified conditions were calculated for continuous and reversal type experiments. In reversal design to have a 90% chance of detecting a mean treatment difference of 25% at 5% significance requires two ejaculates per bull per treatment collected from 3 to 22 bulls, depending on the semen characteristic. For continuous experiments in which each bull receives only one treatment, usually two to three times as many ejaculates (bulls x ejaculates) are needed for similar sensitivity. Optimum design may differ depending upon ages of bulls.

² Present address: Department of Physiology and Biophysics, Colorado State University, Fort Collins 80521.