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Fertility of Unfrozen and Frozen Stallion Spermatozoa Extended in EDTA-Lactose-Egg Yolk and Packaged in Straws¹

Colorado State University³, Fort Collins 80523

² Reprint requests to R. P. Amann.

Abstract

The fertility of frozen-thawed semen was compared with that obtained using fresh semen extended in skim milk. Semen for freezing was obtained in June from four stallions of unknown fertility; two ejaculates were collected 1 to 2 h apart every 3 or 4 d. The gel-free fraction of the ejaculate was mixed 1:1 with a glucose-EDTA solution (disodium ethylenediaminetetraacetic acid) and centrifuged at 650 x g for 15 min. The spermatozoa were resuspended in an EDTA-lactose-egg yolk extender containing 5% glycerol. Semen was frozen in .5-ml French straws containing 250 x 10⁶ progressively motile spermatozoa before freezing. Only for 31% of the 54 ejaculates frozen was post-thaw spermatozoal motility 50% of the percentage of progressively motile spermatozoa observed during evaluation of the neat semen. Spermatozoa in second ejaculates apparently were more susceptible to the adverse effects of dilution and centrifugation than spermatozoa in first ejaculates. Only samples containing 30% progressively motile spermatozoa after freezing and thawing (at 38 C) were used for insemination. In June and July, 101 mares were inseminated daily with semen from one of three stallions beginning on d 2 and continuing through the end of estrus for one cycle. Mares were inseminated with semen in one straw or with 250 x 10⁶ progressively motile spermatozoa extended in 10 ml of skim milk. Because of the poor survival of spermatozoa that had been frozen and thawed, mares inseminated with frozen-thawed semen received 100 to 130 x 10⁶ progressively motile spermatozoa as compared with 250 x 10⁶ progressively motile spermatozoa for mares inseminated with fresh semen. One cycle pregnancy rates, based on rectal palpation 50 to 60 d after ovulation, were 29% using frozen-thawed semen and 66% using fresh semen (P<.05). Values for individual stallions were 19, 24 and 47% with frozen semen and 47, 61 and 67% with fresh semen. Routine use of frozen stallion semen is not recommended at this time.

¹ Appreciation is expressed to Dr. R. K. Shideler and C. M. Clay, V. M. Cook, M. F. Iuliano, J. M. Maher, D. C. Monroe, T. C. Otte and L. Tamlin for their assistance. Supplies for packaging the semen were kindly provided by IMV International, Inc., Minneapolis, MN. The financial support of members of the equine industry, and especially the International Sport Horse Center, is gratefully acknowledged.

³ Anim. Reprod. Lab.