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

Abstract

A group of five Holstein bulls ejaculated once at 8-day intervals for 360 days averaged 10.6 billion motile spermatozoa per ejaculate. In another comparable group ejaculated twice at 8-day intervals during the same period of time the first ejaculates averaged 10.3 billion and the second ejaculates 6.9 billion motile spermatozoa per ejaculate. The average 60- to 90-day per cent nonreturns to first-service cows was 73.3 for the one-ejaculate bulls and 73.6 for the first ejaculates and 73.4 for the second ejaculates from the two-ejaculate bulls. It was estimated that on the basis of the spermatozoa output of the two-ejaculate bulls the ten 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.