Motility of liquid stored ram spermatozoa is altered by dilution rate independent of seminal plasma concentration

The fertility after use of liquid stored ram semen following cervical AI rapidly decreases if semen is stored beyond 12 h. The dilution of seminal plasma is often cited as a key contributor to the diminished motility and fertility of ram spermatozoa subjected to liquid preservation. Two experiments were conducted to assess the effect of spermatozoa concentration (i.e. dilution rate) and percentage of seminal plasma on the motility and viability of liquid stored ram spermatozoa. In Experiment 1, semen was diluted to one of seven concentrations ranging from 0.2 to 1.4 × 109 spermatozoa/ml with milk and assessed for motility after 3 or 24 h of storage at 15 °C. In Experiment 2, semen was collected and washed to remove seminal plasma before re-dilution to 0.2–1.4 × 109 spermatozoa/ml with milk containing 0%, 20% or 40% (final v/v ratio) seminal plasma and assessed for viability and motility after 3 or 24 h of storage at 15 °C. Whereas motility was not affected by spermatozoa concentration after 3 h of storage, the proportion of progressive spermatozoa decreased after 24 h of storage when spermatozoa concentration was greater than 1.0 × 109 spermatozoa/ml. The duration of preservation and the spermatozoa concentration affected spermatozoa motility but had no impact on spermatozoa viability. This negative effect of greater spermatozoa concentrations on motility was independent of the presence and the concentration of seminal plasma. The seminal plasma at both concentrations (20% and 40%) had a protective effect on spermatozoa motility after 24 h of storage. These findings have the potential to improve the efficiency of cervical AI with liquid stored ram semen.