Insemination doses: how low can we go?

This manuscript presents a brief historical review of investigations related to equine artificial insemination. The origin of recommended insemination doses for use fresh, cooled and frozen semen will be reviewed. Over 30 years ago, an insemination dose of 500 x 10(6) progressively motile sperm (PMS) was recommended to maximize pregnancy rates when mares were bred with fresh semen under less than ideal conditions. Since that time, 500 x 10(6) progressively motile sperm has been almost universally accepted as a standard insemination dose, regardless of a stallion's fertility or the refinements that have been made in mare management and semen extenders. Insemination doses for cooled-transported and frozen-thawed semen have also been extrapolated from this dose. Data from a number of studies will be presented which demonstrate the feasibility and rationale of reducing sperm numbers used to breed mares with fresh, cooled and frozen-thawed semen, including the use of deep-horn insemination techniques.