EFFECT OF SEMINAL PLASMA ON MOTION CHARACTERISTICS OF EPIDIDYMAL AND EJACULATED STALLION SPERMATOZOA DURING STORAGE AT 5-DEGREES-C

The objective of this experiment was to examine the effect of seminal plasma on motion characteristics of epididymal and ejaculated equine spermatozoa during storage at 5 degrees C. Epididymal spermatozoa were flushed with either seminal plasma or a skim milk-glucose extender. Ejaculated spermatozoa were collected with extender added 10 minutes after semen collection and addition of extender during ejaculation by placing 50 ml extender in the collection bottle. Semen samples were centrifuged and resuspended with a skim milk-glucose extender containing seminal plasma (0, 5 and 25 %; v/v), prepared from pooled ejaculates from the semen donors. The percentage of motile spermatozoa and the average path velocity were evaluated by computerized semen analysis before and after centrifugation as well as after 24 and 48 h of cooled storage (5 degrees C). In epididymal samples flushed with seminal plasma versus extender, percentage of motile spermatozoa and spermatozoal velocity ws significantly higher before and after centrifugation but not at 24 and 48 h of cooled storage. Method of semen collection did not influence motility of ejaculated spermatozoa before centrifugation. Adding seminal extender during ejaculation had a significant beneficial effect at 0 and 48 h on the percentage of motile spermatozoa but not average path velocity (25 % seminal plasma). There were significant differences between stallions but the stallion/ejaculate-treatment interaction was not significant at 0, 24 and 48 h. Spermatozoal motility during cooled storage of epididymal and ejaculated spermatozoa was significantly better mainteained in samples containing 25 % versus O % seminal plasma. Spermatozoal motility during cooled storage was affected after spermatozoa had been exposed to seminal plasma for only 10 min after ejaculation. To maximize the protective effect of seminal extenders on stallion spermatozoa, extender should be added to semen samples as early as possible.