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CHAPTER 1.3
1.3.2. Dose and dose makes two
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Without a uniform method to analyze an equine semen sample, it will remain very difficult to
determine the optimal sperm dose to maximize the chance to obtain pregnancy. An insemination
dose is in most cases expressed as being equivalent to a particular number of motile spermatozoa. As
such , an inseminate presumed to contain 300 million PMS as assessed with subjective motility
analysis is very likely to actually contain fewer progressive motile cells when the analysis would be
performed using a CASA system implemented with very strict motility criteria. As such the motility of
the spermatozoa in the same inseminate might be different depending on the type of analysis used.
Animal andrology uses the same techniques available as human andrology. However,
veterinary andrology analyses are done in a stochastic, almost randomized way when comparing
different laboratories. This hampers or even renders comparison of results between laboratories
impossible. This lack of analysis standards does not only slow down the scientific progress as far as
research is concerned; it also interferes with business, as the reliable trading of frozen AI doses in
particular is impeded.
The main problems that occur when performing light microscopic evaluations are subjectivity
and variability (Davis and Katz, 1993). Variations of 30 to 60% in sperm motility are reported for
subjective motility analysis of the same ejaculate by different observers (Verstegen et al., 2002).
Objective methods are available, but this objective analysis is not all standardized. Different settings
can be found in literature (Table 2), however, with the current knowledge it is unclear to what extent
these different motility setting affect the analysis outcome. Additionally, a large variety in different
counting chambers is available to use in combination with CASA systems. Different chambers clearly
influence motility parameters of dog and bull spermatozoa (Iguer-ouada and Verstegen, 2001; Contri
et al., 2010; Lenz et al., 2011). To which extent the motility of stallion semen is affected by these
apparent unimportant utensils remains unclear. This is in clear contrast with human andrology where
the preparation of a motility slide should be done following strict criteria (WHO, 2010).
On the other hand, the wide variety of procedures that exist to prepare AI doses provides the
liberty of choosing and adapting protocols to the specified needs of any given stallion. The
abundance in processing procedures requires a uniform way to objectively determine the best
suitable protocol for “problem stallions” and to chase off the ghost stories once and for all. One of
these techniques, frequently used when processing equine semen is centrifugation. Although
frequently used, the influence on equine semen requires further elucidation since there is quite
some misunderstanding and different opinions concerning the sperm losses accompanying aspiration
of supernatant (Weiss et al., 2004; Ecot et al., 2005; Knop et al., 2005).