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Sperm Death and Inhibition of Sperm Transport in the Cervix of Ewes in Estrus After Removal of the Corpus Luteum-Bearing Ovary

US Department of Agriculture, Beltsville, MD 20705

Abstract

Regulation of estrus in the ewe with prostaglandin or progestogen causes death of sperm in the cervix and inhibits sperm transport through the cervix at the regulated estrus. Because removal of the corpus luteum (CL) alters the estrous cycle, experiments were conducted to determine the effect of removing the CL-bearing ovary on sperm survival and transport in the cervix at the ensuing estrus. In the first experiment, the ovary bearing the CL was removed from each of 45 unilaterally ovulating ewes on day 3, 10 or 15 of the estrous cycle (day 0 = first day of estrus). Fifteen ewes from which the non-CL-bearing ovary was removed on day 15 served as controls. Time from surgery until estrus averaged 2.1 to 2.5 days per group. At estrus, each ewe was mated to two rams and necropsied 2 hr later. Sperm were washed from the oviducts, uterus and anterior, middle and posterior one-thirds of the cervix and counted. Removal of the CL-bearing ovary (CLX) decreased (P<.01) the number of sperm recovered, particularly in the anterior one-third of the cervix, where sperm numbers averaged 1.55 million in control ewes, 40,000 in ewes CLX on day 10 and 330,000 and 220,000 in ewes CLX on day 3 or 15. In the next experiment, the CL-bearing ovary was removed from each of 18 ewes on day 10 or 14 of the cycle. Ten ewes from which the non-CL-bearing ovary was removed on day 15 served as controls. Time from surgery to estrus averaged 2.0 to 2.3 days per group. At estrus, ewes were mated to two rams and necropsied 2 hr later. Sperm were flushed from the uterine body, anterior one-third of the vagina, anterior, middle and posterior one-thirds of the cervix. Condition of sperm was assessed by motility estimates, live-dead staining and normality of apical ridges. CLX on day 10 or 14 significantly reduced the percentages of motile sperm, unstained (live) sperm and sperm with normal apical ridges (NAR); reductions were greater in the uterine body and the anterior one-third of the cervix than in the middle and posterior thirds of the cervix (P<.02, .0001 and .0003, respectively, for percentages of motile, unstained and NAR sperm). In the anterior third of the cervix, percentages of motile sperm for control and CLX ewes averaged 30 and 6, respectively; percentages of unstained sperm averaged 58 and 18, and percentages of sperm with normal apical ridges averaged 44 and 12. Immobilization and death of sperm in the reproductive tract were clearly associated with failure of sperm transport after CLX during the estrous cycle.

¹ Reproduction Lab., Animal Science Institute, AR, SEA, Beltsville Agricultural Research Center.

² The authors express appreciation to Caird E. Rexroad, Jr. for statistical analysis of the data; to Douglas Bolt and Rosemary Rollins for conducting the progesterone assays and to Leah Schulman, for evaluating acrosomal morphology.