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Evaluating Bovine Semen I. Influence of the Number of Ejaculates upon Various Physical and Chemical Characteristics and the Relationship Between Those Factors

University of Nebraska

Abstract

A detailed semen analysis by ejaculates of eleven fertile bulls, representing four dairy breeds whose breeding efficiency was supportd with 73 pregnancies is reported. When the first, second, and third ejaculates of the eleven bulls are compared for volume of semen, percentage of progressive motility of spermatozoa, concentration of spermatozoa per mm³, and pH, certain differences are found. The volume remains nearly constant for all ejaculates with notable differences between individual bulls. The mean for 571 samples of semen is 4.2 cc. In motility, the ejaculates rank as follows: second, with a mean of 75 percent; first, with a mean of 73 percent; and third, with a mean of 69. The mean for all 273 ejaculates is 74 percent. The concentrations of spermatozoa per mm³ rank in order as follows: first 826,000, second 635,000, and third 357,000. The mean for all 266 samples was 734,000 per mm³. In pH values the mean for the different ejaculates is as follows: first 6.85, second, 7.23, third 7.21, and for all 237 ejaculates 6.99. Statistical analysis of these factors and their relationships indicates a slight correlation coefficient between volume of semen and percentage of motility, volume of semen and concentration of spermatozoa per mm³, and between percentage of motility and concentration of spermatozoa per mm³. There was a high negative correlation between pH and volume of semen and between pH and percentage of motility. There was a highly significant positive correlation between the concentration of spermatozoa per mm³ and the pH: the higher the concentration the lower the pH value. For actual breeding, the second ejaculates proved slightly more effective in inseminating 35 cows in that 1.250 inseminations were required for each conception as compared with 1.333 for the first ejaculate, when 60 cows were inseminated. For all ejaculates 1.301 inseminations were required for each conception.

^* Now at the University of Vermont. Published with the approval of the Director as Paper No. 253 Journal Series, Nebraska Agricultural Experiment Station.