Evaluation of epididymal semen quality using the Hamilton-Thorne analyser indicates variation between the two caudae epididymides of the same bull

Epididymal semen is being more often considered as a potential source of valuable genes for genome resource banks. To utilize this resource as efficiently as possible, storage and freezing fertility and preservation characteristics of epididymal semen have to be examined. Because semen quality should be assessed as objectively as possible, we introduced computer assisted sperm analysis (CASA) of epididymal bull semen. The aims of this study were: to determine the quality of fresh cauda epididymal bull sperm, conventionally and by CASA (Hamilton-Thorne Ceros 12.1); to compare epididymal sperm movement with the motion characteristics of ejaculated semen; and to investigate whether equality of semen characteristics exists between both caudae epididymides of the same bull. In experiment 1, it is shown that epididymal sperm has a lower motility (total: 48.7% versus 79.9%, p < 0.0001 and progressive: 34.4% versus 58.4%, p < 0.0001) and moves less straight (80.5% versus 84.5%, p < 0.0009) with a higher amplitude (6.1 microm versus 5.0 microm, p < 0.0001) than ejaculated semen. The epididymal straight line velocity (85.2 microm/s versus 98.3 microm/s, p < 0.0001) is lower, but the curvilinear velocity (173.5 microm/s versus 156.4 microm/s, p < 0.0001) is higher than those of ejaculated semen. The data in experiment 2 are analysed to determine equality, rather than to find a difference. They illustrate that mean differences, for most semen parameters, between the semen from paired caudae epididymides, deviated more than 20% from the average values of these parameters from all bulls; the exceptions (those parameters within 20% of the average for all bulls) were the percentage of live spermatozoa, the linearity of sperm movement, the weights of testis and epididymis, the weights of the cauda epididymis alone, the volumes, and the amplitudes of movement of the semen (p < 0.05). The mean differences between the percentage of live spermatozoa and the amplitude of movement of the epididymal semen of both epididymides of one bull, were the only values smaller than 10% of the average value of this parameter (p < 0.05). This implies that sperm from one cauda epididymis should not be used as a control for the other because, for most of the semen parameters (concentration, morphology, motility, and beat cross frequency), equality between caudae epididymides of the same bull could not be established.