The effects of the cervix on the transport of morphologically abnormal spermatozoa in the female bovine
Two studies were conducted to investigate the role of the bovine cervix in filtering abnormal sperm. ln Study 1, semen containing high levels of abnormal sperm was vaginally deposited in 12 cows 80 hours after prostaglandin F₂α treatment. At slaughter, 4-, 8- or 12 hours post-insemination, sperm were flushed from the excised uteri with fixative. Pooled across times post-insemination, viability was greater for uterine vs inseminate sperm, based upon vital smears prepared from inseminate and uterine flush samples. Uterine levels of normal sperm, determined by differential interference contrast (DIC) microscopy, were greater than were inseminated. In Study 2, heifers were estrus synchronized in pairs using prostaglandin F₂α, then inseminated with semen containing high levels of abnormal sperm. In each pair, semen of high viability (Experiment 1, n=10) or low viability (Experiment 2, n=6) was deposited vaginally in one heifer and within the uterine corpus of the other. Using DIC microscopy, viability and morphology were coincidentally determined for sperm in samples from the fixed inseminate and the retrograde mucus, vaginal mucus, cervix, uterus and in vitro incubation of inseminate recovered and fixed 12 hours post-insemination. Uterine sperm quality did not differ between insemination sites, except lower uterine levels of live abnormal sperm alter intrauterine vs vaginal insemination of low viability semen probably due to disproportionately low viability of one abnormality. Sperm viability was enhanced and morphology unchanged in the uterus vs low viability inseminate, while sperm viability was unchanged and abnormal sperm subtly reduced in uterus vs high viability inseminate. Greater levels of live and live normal sperm were found deeper between cervical folds than at apical aspects of folds. Vaginal mucus sperm viability was lower compared to other tract locations and inseminate, especially after high viability insemination. Compared to inseminate viability, retrograde mucus sperm viability was high after vaginal insemination and low alter intrauterine insemination. Differential death of abnormal vs normal sperm neither with incubation of insemination in vitro nor, presumably, in vivo. Results show little evidence of cervical filtration based upon sperm morphology. Sperm retention in the female tract was predominantly related to sperm viability with only very subtle morphology effects.