view - Department of Reproduction, Obstetrics and Herd Health
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view - Department of Reproduction, Obstetrics and Herd Health
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CHAPTER 3.2<br />
102<br />
In veterinary medicine, a number <strong>of</strong> studies have focussed on counting chambers in<br />
combination with CASA devices. Discrepancies between CASA estimates <strong>and</strong> the Bürker<br />
haemocytometer have been described for different species (Rijsselaere et al., 2003; Vyt et al., 2004).<br />
To obtain a sharp image <strong>of</strong> the sperm cells when performing the motility analysis, CASA devices are<br />
primarily used in combination with shallow chambers to keep the moving sperm within focus plane<br />
<strong>of</strong> the microscope. Therefore CASA systems are frequently used in combination with 20 µm deep<br />
disposable counting chambers. These chambers are most <strong>of</strong>ten loaded by capillary force, <strong>and</strong> such a<br />
capillary flow in a 20 µm chamber follows the laminar Poiseuille flow (Douglas-Hamilton et al.,<br />
2005a). This leads to a transverse lifting force on suspended particles <strong>and</strong> results in an unevenly<br />
concentration throughout the sample as described by Segre <strong>and</strong> Silberberg <strong>and</strong> is, as such, known as<br />
the SS effect (Douglas-Hamilton et al., 2005b). The influence <strong>of</strong> this SS effect on the distribution<br />
throughout the slide depends on the viscosity <strong>of</strong> the sample. Correction factors are available <strong>and</strong> are<br />
based on the time it takes for a chamber to be filled, <strong>and</strong> as such determined by viscosity <strong>of</strong> the<br />
loaded sample (Douglas-Hamilton et al., 2005a). Although the SS effect is well documented in<br />
literature, interpretation <strong>of</strong> the results is not always performed correctly. For example, in a recent<br />
study (Maes et al., 2010), two types <strong>of</strong> 20 µm Leja slides were compared, where one <strong>of</strong> the slides<br />
was especially developed to be able to correct for the SS effect. Unfortunately, the results obtained<br />
with the two chambers were compared as such, without applying the correction factor. Therefore it<br />
was faulty concluded that the newly shaped counting chamber was not able to correct for the SS<br />
effect.<br />
CASA instruments were developed to provide a solution for problems linked with subjective<br />
motility analysis. Indeed, subjective assessment <strong>of</strong> motility is known to be inaccurate, imprecise <strong>and</strong><br />
subject to variability (Davis <strong>and</strong> Katz, 1993; Matson, 1995). However, in order for CASA systems to<br />
contribute to a st<strong>and</strong>ardized <strong>and</strong> objective analysis, uniformity in protocols <strong>and</strong> settings is required.<br />
In literature, a large variation in technical settings can be found as well as a lack in uniformity for<br />
preparing a sample for motility analysis. It has been demonstrated that the large variety in motility<br />
settings used influences motility outcomes significantly (Hoogewijs et al., 2009). The chambers used<br />
in combination with CASA are very diverse <strong>and</strong> quite <strong>of</strong>ten not clearly described. As such, it is nearly<br />
impossible to compare results between different studies.<br />
The big difference in loading technique <strong>and</strong> motility outcomes may be attributed by physical<br />
forces on the spermatozoa during loading as postulated by Lenz et al. (2011). When a semen sample<br />
is placed on the loading area <strong>of</strong> a capillarity filled chamber, the flow that occurs might damage the