Estimation of Some Variance Components of Bovine Semen Criteria and Their Use in the Design of Experiments

Abstract

Semen production records of 68 bulls from Ave dairy breeds in four studs were used to estimate the bull, ejaculate, breed, season, and interaction variance components of five criteria used to measure semen production. The means and standard deviations of individual observations for the five criteria were: ml. of semen per ejaculate, 8.0 ± 2.4; per cent motile sperm, 66 ± 9.0; billions of sperm per ml. of semen, 1.71 ± 0.62; billions of motile sperm per ejaculate, 8.9 ± 3.9, and billions of total sperm per ejaculate, 13.6 ± 6.0. Component of variance analyses showed that the bull and ejaculate components accounted for more than 90% of the total variance in all criteria except per cent motile sperm. Consequently, these two variances were taken into account in estimating the power of the test by Tang's method. This estimate showed that there was little increase in sensitivity to be gained by taking more than ten ejaculates per bull. It was calculated that to have a 75% chance of detecting a treatment difference of 50% of the mean of motile sperm per ejaculate at the 5% level of significance would require about ten bulls per treatment and five ejaculates per bull.