Death of sperm in the cervix of ewes bearing intrauterine plastic spirals or threads

Fertility and ovum fertilization rate after laparoscopic or transcervical intrauterine artificial insemination of oxytocin-treated ewes

Based on our previous work, we found that exogenous oxytocin induces uterine tetany and cervical dilation, and permits transcervical access to the uterus. However, the oxytocin does not reduce sustained sperm transport from the uterus to the oviducts. Thus, we hypothesized that exogenous oxytocin may be a useful adjunct to transcervical intrauterine AI procedures for sheep: two experiments were conducted to test our hypothesis. In Experiment 1, purebred ewes (n = 75/group) were artificially inseminated intrauterine with either laparoscopic or oxytocin-transcervical (i.e., 200 USP units of oxytocin 30 min before AI) procedures. At 54 h after progestogenated pessaries were removed, ewes were inseminated with 200 x 10(6) sperm/0.25 ml of fresh, extended semen, which was collected from a purebred ram of the corresponding breed. Pregnancy rate was greater (P < 0.05) after laparoscopic (37.5%) than after transcervical AI (0%). Because of the disappointing results of Experiment 1, Experiment 2 was conducted to determine whether oxytocin or the AI procedure per se reduced ovum fertilization rate. Treatments were designed in a 2 x 2 factorial arrangement. At 60 h after norgestomet implant removal and 10 min before either laparoscopic or transcervical (cervical in a saline group) AI with 100 x 10(6) sperm/0.25 ml, ewes (n = 10/group) received an intravenous injection of either isotonic saline or 200 USP units of oxytocin. Fertilization rate, which was determined 72 h after AI, was greater (P < 0.05) after laparoscopic than after transcervical/cervical AI (92.5 vs 28%), but oxytocin treatment did not affect fertilization rate. The results indicate that exogenous oxytocin did not reduce ovum fertilization rate, but the transcervical AI procedure per se seemed to reduce fertilization rate.

Sperm survival and transport in the female reproductive tract

Fertilization failure, mostly due to absence of sperm in the oviducts, is a major cause of reproductive inefficiency of farm animals. Sperm may be transported to the oviducts of cattle and sheep within a few minutes after mating or insemination, but these sperm probably fertilize few ova. Slower transport, with establishment of sperm populations in each segment of the reproductive tract, requires a few to several hours. In swine, sperm capable of fertilizing ova reach the oviducts in less than 1 h. Smooth muscle contractions of the reproductive tract, ciliary beats, fluid currents, and flagellar activity of sperm are primary mechanisms of sperm transport. Sperm become hyperactive in the oviducts in association with capacitation. Most sperm in an inseminate drain from the female reproductive tract within a few minutes or hours after insemination; remaining sperm are removed from the tract by slower drainage or phagocytosis. Sperm survival and transport in estrous ewes is reduced drastically by pastures with high estrogen content and by regulating estrus with progestogen or prostaglandin F2 alpha. The cervix is the initial site of inhibition of sperm transport in ewes, and endocrine imbalances probably are the basis of inhibition. Sperm transport problems generally are associated with immobilization and death of sperm in the uterus and anterior segments of the cervix within 2 h after mating. After gilts are inseminated with frozen-thawed semen, relatively few sperm are retained in the reproductive tract, apparently accounting for lowered fertilization rates. Sperm transport has been improved by adding to semen or administering to females such compounds as prostaglandin F2 alpha, oxytocin, estradiol, phenylephrine, or ergonovine. Estradiol, prostaglandin F2 alpha, phenylephrine, and ergonovine administered to rabbits at insemination each increased fertilization rates.