Semen Production and Fertility of Mature Dairy Bulls Ejaculated Either Once or Twice at 8-Day Intervals

Abstract

A group of 5 Holstein bulls ejaculated once at 8-day intervals for 360 days averaged 10.6 billion motile spermatozoa/ejaculate. In another comparable group ejaculated twice at 8-day intervals during the same period of time the 1st ejaculates averaged 10.3 billion and the 2d ejaculates 6.9 billion motile spermatozoa/ ejaculate. The average 60- to 90-day per cent nonreturns to 1st-service cows was 73.3 for the one-ejaculate bulls and 73.6 for the 1st ejaculates and 73.4 for the 2d ejaculates from the 2-ejaculate bulls. It was estimated that on the basis of the spermatozoa output of the 2-ejacuiate bulls the 10 bulls in the experiment had a breeding potential under present day operational procedures of nearly three-quarters of a million services and nearly a quarter of a million female progeny. Such potentials emphasize the need for applying the best methods now available for testing and selecting the sires to be used so heavily.