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

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Abstract
A group of 14 dairy bulls ejaculated once at 4-day intervals for 272 days averaged 5.7 billion motile spermatozoa/ejaculate. Another group of 16 bulls ejaculated once at 8-day intervals for 272 days averaged 7.0 billion motile spermatozoa/ejaculate. The average 60- to 90-day per cent nonreturns to more than 25,000 first services/group was 61.8 for the 4-day bulls and 64.8 for the 8-day bulls, a difference that was not statistically significant, P < 0.05. During an 88-day period immediately following the 272-day period the 8-day interval bulls were ejaculated twice every 8th day and averaged 5.7 billion motile spermatozoa/ejaculate and 12.8 billion/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 1st 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 < 0.05.