Semen Production and Fertility of Dairy Bulls Ejaculated Either Once or Twice at Intervals of Either Four or Eight Days

Summary A group of 14 dairy bulls ejaculated once at 4-day intervals for 272 days averaged 5.7 billion motile spermatozoa per ejaculate. Another group of 16 bulls ejaculated once at 8-day intervals for 272 days averaged 7.0 billion motile spermatozoa per ejaculate. The average 60- to 90-day per cent nonreturns to more than 25,000 first services per group was 61.8 for the 4-day biills and 64.8 for the 8-day bulls, a difference that was not statistically significant, P During an 88-day period immediately following the 272-day period the 8-day interval bulls were ejaculated twice every eighth day and averaged 5.7 billion motile spermatozoa per ejaculate and 12.8 billion per 8-day period. The 4-day interval bulls, continued on the original interval between ejaculates, averaged 12.6 billion motile spermatozoa on an 8-day basis during this same period. The 60- to 90-day per cent nonreturns to first services was 65.2 for the 4-day bulls and 67.9 for the 8-day bulls. Again, the difference was not statistically significant, P It is concluded that one ejaculation every fourth day or two ejaculations every eighth day for periods as long as 1 year are not detrimental to semen production or fertility and that ejaculations at a rate of two per 8-day interval will yield about 60% more motile sperm than will ejaculations at the rate of one per 8-day interval.