Individual fertility differences in the frozen-thawed spermatozoa among semen donors in the Labrador Retriever.

Purpose: We aimed to validate and determine the possible application of transcervical insemination of frozen semen for improved breeding in guide dogs for the blind in Japan.
Methods: From February 2004 to March 2007, a total of 53 Labrador Retriever bitches, used for the breeding of guide dogs for the blind, were transcervically inseminated with frozen-thawed semen from 13 males by means of a cystoscope.
Results: The overall whelping and pregnancy rate with the frozen semen was 42%. Pregnancy rates ranged widely from 0 to 100% depending on the semen donor male. Of 13 males, 6 males exhibited severely poor fertility (less than 20% pregnancy rate) and 3 males exhibited high fertility (over 70% pregnancy rate) on artificial insemination. However, the spermatozoa motility after thawing was not significantly different among these dogs. In addition, heterospermic insemination revealed the optimal timing for transcervical insemination with frozen-thawed semen to be by day 6 after the LH surge. Conclusions: Although transcervical insemination of frozen-thawed semen is effective for breeding of guide dogs for the blind, some modification of freeze-thawing procedures might be required to overcome individual fertility differences in the frozen-thawed spermatozoa among semen donor dogs,. In addition, the motility of spermatozoa after thawing might not be an appropriate indicator of the relative fertility of frozen-thawed spermatozoa in dogs.