Introduction
The ideal method for processing semen for use with either fresh or cooled-shipped breeding would maximize the number or sperm per mL, maximize total number of progressively motile sperm, minimize the volume needed to breed a mare, not be deleterious to sperm function or longevity and minimize seminal plasma. Based on these criteria, cushion centrifugation is currently the best method. Cushion centrifugation maximizes sperm recovery compared to sperm filters(Roach et al., 2016) and centrifugation without cushion. Seminal plasma is removed, which can be deleterious to sperm longevity(Braun et al., 1994; Jasko et al., 1991), allows for the semen to be reconstituted more concentrated than simple dilutions, which reduces the volume of the breeding dose while increasing the number of sperm which inseminated into a mare.
Simple dilution of semen is perhaps the oldest method to extended semen for artificial insemination with either fresh or cooled. This was developed prior to the optimization centrifugation techniques for semen through a combination of trial and error and research. Simple dilution is a faster method to process semen, easy to use and works in many circumstances. A variety of other techniques have been developed, such as density gradient centrifugation, which can be used to remove abnormal sperm and sperm filters which may be useful when a centrifuge is unavailable. This review will discuss these techniques in the application of processing equine semen for either fresh or cooled-shipped use.