Factors affecting the analysis and interpretation of sperm quality in frozen/thawed stallion semen.

In the current study, we examined: 1) the agreement (bias) between fluorescence-based methods (NucleoCounter-SP100 [NC] vs. flow cytometry [FC]) for determining the viability (VIAB) of frozen/thawed stallion sperm; 2) the agreement between post-thaw sperm total motility (TMOT) and VIAB; 3) whether a difference between TMOT and VIAB [VIAB – TMOT] in frozen/thawed stallion sperm could be explained by the level of lipid peroxidation in viable sperm (VLPP); 4) the repeatability of post-thaw analysis of sperm quality; and 5) the effect of final post-thaw semen dilution (10, 30, or 50 x 106 sperm/mL) on sperm motion characteristics. Post-thaw VIAB was similar between NC and FC (P > 0.05), and the agreement between these two methods was high (bias : 1 to −3). The agreement between post-thaw TMOT and VIAB decreased as the pre-freeze percentages of morphologically normal sperm and DNA quality decreased: bias – 4 to – 25. The bias between [VIAB – TMOT] and VLPP ranged from – 5 to 7. Differences in post-thaw sperm quality (TMOT, PMOT, VIAB, and sperm concentration) were not observed when analyzing one or three straws per ejaculate (P > 0.05). There was no effect of post-thaw sperm concentration (i.e., 10 vs. 30 vs. 50 x 106 sperm/mL) on sperm motion characteristics (P > 0.05). This study reports factors other than post-thaw sperm motility that warrant further consideration when analyzing frozen/thawed stallion sperm. • Post-thaw sperm viability was similar between NucleoCounter and Flow Cytometry across multiple levels of measurement. • The agreement between post-thaw motility and viability decreased as the intrinsic sperm quality decreased. • Lipid peroxidation was associated with reduced motility in the face of high viability in fresh but not frozen/thawed sperm. • Analysis of one straw per ejaculate yielded similar results than analyzing three straws per ejaculate. • Increasing the sperm concentration in thawed semen prior to motility analysis did not affect the CASA outcomes. [ABSTRACT FROM AUTHOR]