Distribution and viability of spermatozoa in the canine female genital tract during post-ovulatory oocyte maturation

Abstract

BackgroundUnlike other domestic mammals, in which metaphase-II oocytes are ovulated, canine ovulation is characterized by the release of primary oocytes, which may take 12 to up to 36 hours. Further 60 hours are needed for maturation to secondary oocytes which then remain fertile for about 48 hours. Oestrus takes 7 to 10 days on average and may start as early as a week before ovulation. This together with the prolonged process of post-ovulatory oocyte maturation requires an according longevity of spermatozoa in the female genital tract in order to provide a population of fertile sperm when oocytes have matured to fertilizability. Therefore the distribution and viability of spermatozoa in the bitch genital tract was examined during post-ovulatory oocyte maturation.MethodsThirteen beagle bitches were inseminated on the day of sonographically verified ovulation with pooled semen of two beagle dogs containing one billion progressively motile spermatozoa. Ovariohysterectomy was performed two days later (group 1, n = 6) and four days later (group 2, n = 7). The oviduct and uterine horn of one side were flushed separately and the flushing’s were checked for the presence of gametes. The oviducts including the utero-tubal junction and the uterine horns, both the flushed and unflushed, were histologically examined for sperm distribution.ResultsThe total number of spermatozoa recovered by flushing was low and evaluation of viability was limited. Prophase-I oocytes were collected from oviduct flushing in group 1, whereas unfertilized metaphase-II oocytes were detected in group 2. From day 2 to day 4 after ovulation a significant decrease in the percentage of glands containing sperm (P<0.05) and a marked reduction of the mean sperm number in uterine horn glands were observed. A concomitant diminution of spermatozoa was indicated in the utero-tubal junction accompanied by a slight increase in sperm numbers in the mid oviduct.ConclusionsOocyte maturation to metaphase-II stage is accompanied by a continuous sperm detachment and elimination in the uterine horns. Entrance of spermatozoa into the caudal oviduct seems to be steadily controlled by the utero-tubal junction thus providing a selected sperm population to be shifted towards the site of fertilization when oocyte maturation is completed.

Sperm selection in the female mammalian reproductive tract. Focus on the oviduct: Hypotheses, mechanisms, and new opportunities

“…Similarly, a previous study [20] found 75,923 spermatozoa in the UTJ of preovulatory pigs but less than 3000 in the isthmus. Studies of sperm migration in dogs also found that the UTJ effectively controlled the progress of spermatozoa into the oviducts from binding sites situated in the uterus [21]. These studies imply that the UTJ prevents about 90% of uterine spermatozoa from reaching the oviducts.…”

Biología Gestacional y Predicción del Parto en la Perra

“…Además, una población seleccionada de espermatozoides se almacena en la unión útero-oviductal, y un nú-mero limitado de estos continúan liberándose hacia el oviducto caudal en la medida que el ovocito termina su proceso de maduración. Al alcanzar el ovocito el estado de metafase II, una población aún menor de espermatozoides se desplaza hacia el sitio de fecundación (Karre et al, 2012).…”

Current Knowledge on the Transport and Fate of Spermatozoa in the Reproductive Tract of the Bitch

“…From day 2–4 after ovulation, a significant decrease was observed in the percentage of glands containing sperm in combination with a marked reduction of the mean sperm number in the glands of the uterine horn and a diminution of spermatozoa in the uterotubal junction (Karre et al. ).…”

“…; Karre et al. ; England et al. ) and at the glandular mound of the distal part of the uterotubal junction (England and Burgess ; Rijsselaere et al.…”

“…; Karre et al. ; England et al. ), both after natural mating and artificial insemination, indicating that these sites probably act as the major sperm reservoirs in the bitch.…”