Sources of variation of semen output.

Data from 5033 ejaculates during 1 yr from 55 mature Holstein bulls were analyzed to determine the effects of ejaculate number, days between ejaculates, month of the year, solunar periods, and sires on spermatozoal output and seminal characteristics. First ejaculates contained 49.7% more sperm and 40.8% more sperm per ml than second ejaculates. Increasing the interval between collections from 2 to 6+ days resulted in 45.9% more sperm per ejaculate, 31.0% more sperm per ml. and 14.0% greater volume. However, daily sperm output was highest when bulls were ejaculated most frequently. Lowest semen output was in February and March, associated with a decrease in sperm per ml. Highest semen output was in April and June, associated with the highest concentration of sperm per ml. Solunar periods had no effect on any measure of semen output. The concentration of sperm per ml varied more than the volume per ejaculate and had the largest influence on variation in total sperm harvested per ejaculate. Frequency of ejaculation was a major factor in total sperm harvested per bull per year.