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CHAPTER 1.2
36
→ Colloid centrifugation
Centrifugation of semen through (one or more) layers of colloid can be used to separate
spermatozoa from seminal plasma and to select a subpopulation of spermatozoa with good motility,
viability and chromatin integrity (Pertoft, 2000). The cells move to the point in the gradient which
matches their density, i.e. the isopycnic point, during centrifugation (Fig. 10) (Pretlow and Pretlow,
1989), rather than actively swimming through the colloid (Mortimer, 2000). After colloid
centrifugation, the sperm pellet is resuspended in fresh extender (washing medium) and washed by
centrifugation. Percoll® was the first colloid used for the selection of spermatozoa. In 1996, Percoll®
was restricted for non-clinical use only, due to possible toxicity of the product (Avery and Greve,
1995; Mortimer, 2000). Different colloids have been developed, and this has also resulted in species
specific products. Until recently, the major disadvantage of colloid centrifugation was the limitation
in volume that could be processed per centrifugation tube, and the time consuming practice of
carefully preparing the different layers of the Density Gradient Centrifugation (DGC) (Morrell and
Rodriguez-Martinez, 2009).
Fig. 10. Schematic presentation of spermatozoa following colloid centrifugation with location of the
spermatozoa according to their differences in isopycnic point based on their morphology.
Single Layer Centrifugation (SLC) was described as an alternative to DGC for processing
animal semen, resulting in comparable sperm yield and similar sperm quality characteristics (Morrell
et al., 2008; Thys et al., 2009). Additionally, SLC can be used to process larger volumes of extended
semen (Morrell et al., 2009) per centrifugation tube, allowing for the processing of entire stallion
ejaculates.