Hysteroscopic insemination of small numbers of spermatozoa at the uterotubal junction of preovulatory mares

Mares were inseminated with motile spermatozoa suspended in 30-150 mu l Tyr ode's medium directly onto the uterotubal papilla at the anterior tip of th e uterine horn, ipsilateral to the ovary containing a dominant preovulatory follicle of greater than or equal to 35 mm in diameter, by means of a fine gamete intrafallopian transfer (GIFT) catheter passed through the working channel of a strobed light videoendoscope. Insemination of 10, 8, 25, 14, 1 1 and 10 mares with, respectively, 10.0, 5.0, 1.0, 0.5, 0.1 or 0.001 x 10(6 ) motile spermatozoa resulted in conception rates of, respectively, 60, 75, 64, 29, 22 and 10%. Deposition of 1.0 x 106 motile spermatozoa onto the ut erotubal papilla began to approach the limit of successful fertilization. T hese doses are far lower than the 3-15 x 10(9) spermatozoa normally ejacula ted by fertile stallions during mating, and the accepted minimum dose of 50 0 x 10(6) spermatozoa used for conventional uterine body insemination in ma res. The simplicity of the technique offers a practical means of exploiting new breeding technologies that require very small numbers of spermatozoa i n horse breeding.