CASA assessment of kinematic parameters of ram spermatozoa and their relationship to migration efficiency in ruminant cervical mucus.

Sperm motility is an indicator of male fertility because of its importance for sperm migration through the female genital tract and for gamete interaction at fertilization. This study analyses the relationship between computer assisted semen analysis (CASA) motility patterns and sperm migration of rams in ruminant cervical mucus. In experiment 1, spermatozoa extended with sperm analysis medium (SAM) and seminal plasma were compared in terms of motility. In experiment 2, 56 semen samples were collected either with artificial vagina (AV) or electroejaculator to be compared in terms of motility performance. In experiment 3, 104 ejaculates collected by AV from 26 males were analysed via the CASA system to characterize their motility patterns. In experiment 4, ejaculates from pairs of rams (20 rams in total) were simultaneously assessed for mucus migration (ovine, caprine, bovine) and motility patterns to evaluate the correlations between both parameters. Semen collected by AV and extended in SAM allows the most reliable assessment for sperm motility. Ram spermatozoa move fast and follow a linear trajectory compared with other ruminants. Continuous line velocity (VCL) and average path velocity (VAP) are the only sperm kinematic parameters that presented significant positive correlations with the ability to migrate in sheep cervical mucus (p < 0.05). Continuous line velocity, VAP, straight line velocity and linearity are highly significantly related with migration efficiency in goat cervical mucus (p < 0.01) and only lateral head displacement is negatively related to sperm migration in bovine cervical mucus (p < 0.05). These results suggest that specific kinematic parameters confer the ability of spermatozoa to colonize and migrate through epithelial mucus with different rheological properties.