Campus Units

Animal Science, Veterinary Clinical Sciences

Document Type


Publication Version

Published Version

Publication Date


Journal or Book Title

Journal of Equine Veterinary Science





First Page


Last Page





Pregnancy rates reported after artificial insemination with frozen–thawed jack spermatozoa have been relatively low compared with those attained in other species. Cholesterol is known to influence post-thaw fertility of both jack and stallion semen, and altering the amount of cholesterol in the freezing extender may help improve the fertility of frozen–thawed jack semen samples. In this study, we report clinical work that was performed using semen samples collected from a single jack. Samples were extended in EZ Mixin OF and then slowly cooled to 5°C. Extended semen samples were centrifuged at 400 × g for 10 minutes and the supernatant was discarded. Spermatozoa were resuspended in freezing medium to a final concentration of 400 × 106 cells/mL and were later frozen in liquid nitrogen vapor. Freezing extender treatments containing 2% ethylene glycol included the following: (1) 20% egg yolk (EY), (2) 5% EY, and (3) 20% EY + 60 mM hydroxypropyl-β-cyclodextrin (β-CD). For this study, a total of 28 mares aged 2 to 18 years was used over five breeding seasons (82 total cycles). Mares were administered human chorionic gonadotropin to induce ovulation when the dominant follicle was ≥35 mm in diameter. They were inseminated within 6 hours before ovulation and again within 6 hours after ovulation. Pregnancy rates obtained were as follows: (1) 6.25% (one of 15 matings) for 20% EY, (2) 46.5% (20 of 43 matings) for 5% EY, and (3) 58.5% (14 of 24 matings) for 20% EY + 60 mM β-CD. These data suggest that binding of cholesterol with β-CD enhances post-thaw fertility of jack semen samples. We conclude that acceptable pregnancy rates could be achieved with frozen–thawed jack semen samples cryopreserved in 5% EY or 20% EY + 60 mM β-CD using direct post-thaw insemination.


This article is published as Jepsen, Rebecca J., Lawrence E. Evans, and Curtis R. Youngs. "Use of direct thaw insemination to establish pregnancies with frozen–thawed semen from a standard jack." Journal of equine veterinary science 30, no. 11 (2010): 651-656. doi:10.1016/j.jevs.2010.10.001.


Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted.



File Format