Processing stallion semen for on-farm use and cooled transport

Simple dilution of semen is the oldest method to process semen for artificial insemination with either fresh or cooled semen. This was developed prior to the optimisation of centrifugation techniques for semen processing through a combination of trial and error and research. Simple dilution is a faster method to process semen, is easy to use and works in many circumstances. For on-farm semen use a 1:1 (v/v) semen to extender ratio is used. A variety of other techniques have been developed, such as cushion centrifugation, density gradient centrifugation and sperm filtration. Cushion centrifugation is used to concentrate the sperm and allows higher centrifugation speeds than centrifugation alone. This allows for improved recovery rates of sperm. Density gradient centrifugation has been used to select for morphologically normal sperm but suffers from low recovery rates. Processing sperm with this technique can result in improved motility and improved DNA integrity of sperm. Sperm filtration is another method to concentrate sperm without the use of centrifugation; however, it has lower recovery rates compared to cushion centrifugation. This review will discuss these techniques in the application of processing equine semen for either fresh or cooled-shipped use.