The Relationship Between Fertility and the Number of Spermatozoa Inseminated

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Abstract
Three groups of approximately 4100 first service dairy cows were each inseminated artificially with 3 different concentrations of motile spermatozoa, estimated to be 14.3 x 106, 9.5 x 106 and 4.7 x 106; the 60- to 90-day % nonreturns were 70.5, 70.9 and 66.7, respectively. The relatively small loss in fertility accompanying the reduction in the number of motile spermatozoa inseminated from 9.5 x 106 to 4.7 x 106, offers considerable opportunity for reducing the number of bulls needed to breed a particular cow population and, consequently, makes possible a substantial increase in the genetic merit of the bull stud, provided adequate criteria for selection are used.