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5.1
Semen (motility) Analysis
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Spermatozoal motility is likely to remain one of the hallmarks of semen evaluation (Varner,
2008). Still, the wide variety in settings and the use of many different chambers described in
literature clearly indicates that objective motility analysis does not equal standardized analysis.
5.1.1. Technical settings in CASA systems
The results from this thesis clearly state the influence of different motility settings when
using computer assisted sperm analysis (CASA) for the analysis of equine semen motility (Chapter
3.1). Although this influence had not been described previously, these findings are not surprising and
can be easily explained. Analysis by means of CASA is based on the relative position changes of the
head of a sperm cell as illustrated in Fig.1. As such, different trajectory parameters are calculated,
which are used to determine a sperm cell as being motile, progressive motile or static. It is logical
that changing the cut-off values (low and medium VAP cut-off and STR) will result in changes of the
outcomes. After all, a sperm cell with a VAP of 30µm/s and a STR of 50% is progressive motile
according to the settings of Varner’s lab (Waite et al., 2008), whereas according to the settings of
Loomis and Graham (2008) this same sperm cell would be assigned as motile. For analysis of equine
semen, more than ten different motility settings have been reported (reviewed in the general
introduction). For other species the variety in technical settings is as wide. The importance of
agreement of settings will become more pressing when global guidelines on AI doses would be
established.
Additionally, it is not completely clear how CASA systems from different manufacturers calculate
motility, progressive motility and subdivide sperm populations into rapid, medium and slow (WHO,
2010). Two different CASA systems (Ceros Hamilton-Thorn and ISAS Proiser) reported slightly
different results, although analyses of the same samples agreed well when using the same settings
and counting chamber (Hoogewijs, unpublished data). It should not be difficult to persuade the
industry to imply the same mathematical calculations in their device, once the andrologists have
come to an agreement. After all, non-conformity could result in non-approval of the devices from
that company.