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Increased Sperm Death in the Cervix and Uterus of Estrous Ewes after Regulation of Estrus with Prostaglandin or Progestogen

US Department of Agriculture, Beltsville, MD 20705

Abstract

One-hundred and twenty-three ewes were used in three experiments designed to determine whether the regulation of estrus, by administration of either prostaglandin F₂: (PG) to regress corpora lutea or medroxyprogesterone acetate (MAP) to control the length of the estrous cycle, would increase sperm death in the reproductive tract at the ensuing estrus. Ewes were treated either with PG injected IM on day 10 of an estrous cycle or with a MAP-impregnated intravaginal sponge from day 6 to 14 or from day 10 to 23. Ewes were in estrus and were mated 2 days after PG treatment and 2 or 3 days after withdrawal of MAP sponges. Control ewes were mated at a natural unregulated estrus. Ewes were necropsied at 2 or 4 hr after mating. Sperm were washed from the uterine body; from the anterior, middle and posterior thirds of the cervix, and from the anterior vagina (Exp. 1 and 2), or from only the three segments of the cervix (Exp. 3). Viability of sperm was assessed from motility estimates, by live-dead staining and by acrosomal morphology. In the first two experiments, PG or MAP treatment significantly reduced the percentages of sperm that were motile and unstained and had normal acrosomes. Reductions were greater in the uterine body and anterior third of the cervix than in the middle and posterior thirds of the cervix (for PG-treated ewes, P = .004 for motile sperm, P = .0001 for unstained sperm and P = .001 for sperm with normal acrosomes). Thirty-three percent of the sperm were motile in the anterior third of the cervix of control ewes, and 10% were motile in the anterior third of the cervix of PG- and MAP-treated ewes; 61% of the sperm were unstained in the anterior cervix of control ewes and 18% were unstained in treated ewes. In Exp. 1 and 2, the concentration of sperm in washings of the anterior third of the cervix was lower for treated ewes than for control ewes. In the third experiment, sperm numbers in the anterior cervix of control ewes were reduced to the numbers in PG- and MAP-treated ewes by use of artificial insemination or by removal of semen from the vagina after natural mating. Treated ewes were mated naturally and semen was not removed. Thirty-five percent of the sperm were motile in the anterior third of the cervix of control ewes, and 13% were motile in PG- or MAP-treated ewes (P = .0003); 62% of the sperm were unstained in control ewes and 22% were unstained in treated ewes (P = .0001). Apparently, sperm death in treated ewes was caused mostly by something other than low sperm numbers. Death of sperm in the cervix may be a major factor in the reduction of the number of sperm that reach the anterior cervix, uterus and oviducts of ewes during regulated estrus.

¹ Reproduction Lab., Animal Science Institute, AR, SEA. The authors express appreciation to The Upjohn Company, Kalamazoo, MI, for supplying prostaglandin and medroxyprogesterone acetate; to Caird E. Rexroad, Jr., for statistical analysis of the data, and to Leah Schulman, for evaluating acrosomal morphology.

² Mention of a trade name or proprietary product does not constitute a guarantee or warranty by the USDA and does not imply approval to the exclusion of others not mentioned.