EFFECT OF SEMINAL PLASMA DILUTION OR REMOVAL ON SPERMATOZOAL MOTION CHARACTERISTICS OF COOLED STALLION SEMEN

Centrifugation of stallion semen to remove seminal plasma was hypothesized to be potentially beneficial in maintaining spermatozoal motility during cooled storage of extended semen. This hypothesis was tested using a series of experiments that evaluated spermatozoal motion characteristics, as determined by computerized semen analysis, of extended, cooled stallion semen. In the first experiment, aliquots of semen were extended to 50 x 10(6) sperm/ml with a nonfat, dried skim milk solids-glucose semen extender and subsequently were cooled slowly to 5-degrees-C and stored for 24 hours. Those aliquots utilizing high dilution ratios of extender (> 1:2.1, volume of semen:volume of extender) maintained higher spermatozoal motility and mean velocity than aliquots using a lower dilution ratio. In the second experiment, semen was extended to 50 x 10(6) sperm/ml and centrifuged at 500 x g for 18 minutes. The sperm pellet was resuspended without the removal of extended seminal plasma. An immediate and significant (P < 0.05) decrease in spermatozoal motility and mean velocity was noted when compared with noncentrifuged samples. However, after 24 hours of cooled storage, no apparent differences in spermatozoal motility or mean velocity between centrifuged and noncentrifuged samples were identified. In the third experiment, semen was extended to 50 x 10(6) sperm/ml and centrifuged at 500 x g for 18 minutes, with the subsequent removal of extended seminal plasma and resuspension of the sperm pellet in fresh extender. A significant (P < 0.05) improvement in the maintenance of spermatozoal motility and mean velocity after 24 hours of cooled storage was evident when compared with centrifuged samples retaining seminal plasma. Furthermore, the removal of seminal plasma by semen centrifugation resulted in similar maintenance of spermatozoal motion characteristics after 24 hours of cooled storage for samples stored at 25, 50, and 100 x 10(6) sperm/ml.