Equine spermatozoal motility and fertility associated with the incorporation of d-(+)-mannose into semen extender

Mannose is capable of decreasing bacterial attachment to the uterine mucosa in mares. Bacteria gain entry into the mare's uterus during breeding; therefore, a practical method to deliver mannose to the uterus is to incorporate it into semen extenders. The effect of mannose on spermatozoal motility and subsequent sperm fertilizing capability is unknown. The present study evaluated progressive spermatozoal motility in semen extender formulations incorporating mannose and assessed the fertility of mares inseminated with a mannose-containing semen extender. In Experiment 1, progressive spermatozoal motility in extender mixtures containing 0 mannose (control), 25, 37 or 49 mg/mL mannose was evaluated at 20 °C or 5 °C holding temperatures for 0, 12, 24 and 48 h post-dilution. Measures were repeated three times using five stallions of proven fertility. High concentrations of mannose in the extender affected progressive motility beyond the time and temperature effects noted in the controls. Extender containing only mannose sugar (49 mg/mL) displayed an immediate depression in progressive motility compared with controls (45.5% versus 62.9%, respectively; P < 0.001). The 37 mg/mL mannose extender had a less dramatic decrease in motility (P < 0.05) and only after storage at 5 °C for ≥12 h (48.7% versus 58.0%, respectively). Extender with 25 mg/mL mannose performed no differently than the control formulation under all conditions. In Experiment 2, two groups of mares (n = 11 each) were inseminated with 500 × 106 progressively motile spermatozoa extended in a traditional skim milk (control) extender or the 37 mg/mL mannose extender preparation. A single-cycle pregnancy rate of 72% was achieved by both groups. Present data suggest that a semen extender containing up to 37 mg/mL mannose could maintain motile spermatozoa for on-farm use and 25 mg/mL mannose concentrations preserved motility during long-term cooling. Likewise, sperm extended with up to 37 mg/mL of mannose had the same fertilizing capability as sperm in traditional extender mixtures.