Evaluation of a Chemically Defined, Long-Term Extender for Liquid Storage of Stallion Semen

Efficient use of stallion semen in liquid state is limited by its relatively short shelf-life. A chemically defined extender (Beyond) is now available for long-term liquid semen preservation. The objectives of the present study were to compare Beyond with milk extenders for the preservation of semen at two temperatures, and to evaluate fertility of semen cooled for 4-8 days before artificial insemination. Semen was processed using different extenders: milk, cholesterol (BotuSemen Special); milk-based (INRA 96); and Beyond. Sperm motility, membrane and acrosome integrity, and chromatin structure were evaluated in semen stored at 17°C for 7 days or at 5°C for 14 days. Sperm motility decreased in the first few days of storage regardless of extender or storage temperature. Sperm motility continued to decline at relatively constant rates in semen extended in milk extenders, but the rate of decline was substantially reduced with Beyond. Sperm motility in semen extended with Beyond was greater than in semen extended with milk extenders after 4 days of storage at 17°C, or after 7 days of storage at 5°C. Extender did not affect sperm DNA damage during storage, but sperm with intact membrane and intact acrosome were lower with Beyond. Inseminations with semen stored with Beyond at 5°C for an average of 5.5 days resulted in embryos in 61% of cycles (11/18). In conclusion, Beyond extender resulted in greater sperm motility longevity when compared to milk extenders, especially when semen was stored at 5°C. Satisfactory fertility was obtained with semen cooled for 4-8 days before artificial insemination.