Laboratory Tests, Singly and in Combination, for Evaluating Fertility of Semen and of Bulls

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Abstract
Three trials in which correlations between nonreturn rates and single laboratory tests or combinations of tests for measuring fertility of semen were completed. In each trial there were from 26 to 72 samples and a total of from 7,577 to 15,376 services/test. The only correlation coefficients with a magnitude of 0.9 or higher, and thereby enabling fairly accurate prediction of fertility by laboratory tests, were those among bulls between nonreturn rate and (a) motility of spermatozoa after incubation at 38[degree]C in yolk-citrate plus antibacterial agents and (b) the combination of methylene blue reduction time, drop in progressive motility after 120 minutes in 3% aniline blue solution at 4[degree]C, and initial total motility in yolk-citrate-sulfanilamide. With additional testing on an a priori basis in Trial II, the correlation for this combination was only 0.73, and in Trial III under field conditions, 0.55. The among-bull correlations were, in most instances, higher than the total or within-bull correlations. This fact indicates that the possibility of estimating differences in fertility among bulls is more promising than estimating differences among individual semen samples.