Effect of heterologous and homologous seminal plasma on stallion sperm quality

Removing most of the seminal plasma (SP) from stallion semen has been shown to improve survival during cooled storage, yet adding small quantities of SP may improve pregnancy rates or cryosurvival. Furthermore, there is considerable controversy about whether the stallion's own SP or heterologous SP produces the best effect, possibly because of the variation between stallions in SP proteins or because some homologous SP remained in the sperm preparation. The SP is removed completely from stallion spermatozoa prepared by colloid centrifugation. Thus, the aim of the present study was (1) to investigate the effect of adding back SP to colloid centrifuged spermatozoa to determine its effect on spermatozoa; and (2) to investigate whether the stallion's own SP had a greater or lesser effect than heterologous SP. Conventional semen doses were sent from a stud overnight to the laboratory using standard transport conditions. Once at the laboratory, the semen samples were used for single layer centrifugation with Androcoll-E, and the resulting sperm preparations were treated with heterologous SP. Adding SP had a small but significant effect on sperm motility but no effect on the proportion of spermatozoa that had acrosome reacted. There were significant increases in hydrogen peroxide production and chromatin damage (P < 0.001). When homologous and heterologous SP were compared, considerable variation was observed between stallions, so that it was not possible to predict whether homologous or heterologous SP, or no SP, will produce the best motility for spermatozoa from any given stallion. Therefore, it is necessary to test different combinations of spermatozoa and SP to find the optimal effect on motility. The SP from most stallions increased reactive oxygen species and chromatin damage. In conclusion, the interaction between SP and spermatozoa depends on the origin of both SP and spermatozoa. If it is desirable to add SP to stallion sperm samples, it should be done directly before insemination rather than before storage, because of increased hydrogen peroxide production and sperm chromatin damage.