Role of Epididymal Proteins and Mannose on Sperm Longevity

In the epididymis sperm are stored for an extended period of time, but upon ejaculation motility is increased and lifespan decreased from several weeks to hours. It has been suggested that proteins present in the environment may play a role in sperm longevity. Some of these proteins are the ones needed to metabolize mannose, a slow-burning sugar. Thus, the objective of this experiment was to investigate the effect that different culture mediums might have on sperm longevity. Semen from 10 bulls was collected via electroejaculation and cultured in 1) a commercial extender, 2) a commercial extender plus mannose, 3) epididymal fluid, 4) epididymal fluid plus mannose, 5) sperm stripped of surface proteins and cultured in a commercial extender, and 6) sperm stripped of surface proteins and cultured in epididymal fluid. Sperm were stained with Hoerscht 33258 and evaluated on days 0, 1, 3, 7, and 10 for motility, velocity, progressive motility, and viability using a Computer Assisted Sperm Analysis (CASA) system. Both treatment and time influenced motility (P < 0.01). Motility of all treatments decreased over time, and sperm stripped of surface proteins prior to culture had decreased motility compared to sperm from which proteins were not removed (11.0% ± 2.0% vs 18.5% ± 2.4% and 12.9% ± 2.1% vs 21.4% ± 2.0% for commercial extender and epididymal fluid). Curve linear velocity was also decreased over time, but of the sperm that were motile, sperm with proteins stripped and cultured in a commercial extender tended (P < 0.10; 62.3 ± 4.3) to have greater velocity than other sperm (49.4 ± 4.6, 52.6 ± 48.4 ±4.2, 48.4 ± 4.2, 47.3 ± 4.2, 46.3 ± 4.3 for 1, 2, 3, 4, and 6). Progressive motility was not influenced by treatment (P = 0.72). However, viability was impacted by both treatment and time (P < 0.01). Viability decreased over time, but sperm cultured in commercial media alone had decreased viability compared to all other treatments. Commercial media with mannose also had decreased viability compared to epididymal fluid with mannose (84.9% ± 2.5% vs 92.1% ± 2.5%). In conclusion, the removal of surface proteins from the sperm after ejaculation greatly decreased overall motility, but the addition of mannose, a sugar for which enzymes to utilize were found in both epididymal and ejaculated fluid, increased viability of sperm cultured both in a commercial media and in epididymal fluid.