Factors affecting the plasma membrane function of cooled-stored stallion spermatozoa

The use of cooled-shipped semen has become a routine method in the equine industry and semen stored at 5 °C for about 24 h maintains fertility close to that of fresh semen. According to the suitability of their ejaculates for cooled-storage, stallions may be classified as “good coolers” or “poor coolers”. Semen processing involves a number of factors that may damage the sperm plasma membrane. This includes addition of semen extender, centrifugation, cooling and storage at a temperature of 4-6 °C. Extender media and their ingredients protect the sperm plasma membrane against environmental influences, but unsuitable composition of the extender can also promote membrane damage. Recent advantages in extender composition are based on the substitution of undefined factors such as milk or egg yolk by more defined and stable components.