Reprint of: Seasonal Influences on Cooled-Shipped and Frozen-Thawed Stallion Semen

• Stallions are fertile throughout the year.
• Differences in quality of processed equine semen among seasons are small.
• Consideration of seasonal differences may help to improve the productivity of stallions.

This review summarizes and discusses results from studies addressing the question if equine spermatozoal function is compromised outside the breeding season resulting in an inferior quality of processed semen obtained at certain times of the year. Differences among studies with regard to the time of the year best suited for cryopreservation may be caused by differences among methods applied to assess semen quality, stallions, and location. Nevertheless, researchers agree that differences among seasons are at best small and variation in the suitability of individual stallions for semen cryopreservation is obviously much more important. Less information is available with regard to cooled-stored semen quality among seasons. Because of the fact that early in the breeding season the number of artificial insemination (AI) doses needed per day is much lower than later in the season, the number of progressively motile spermatozoa per AI dose is usually high. This may counterbalance a decreased longevity of cooled-stored semen produced early in the year. Reduced gonadotropin release during winter is assumed to be the underlying cause of lower semen quality at this time of the year.