Sperm distribution in the oviduct and uterus of mares within two hours after artificial insemination

Our objective was to determine the sperm distribution in the uterus and the number of sperm cells that reach the oviducts after 0.5, 1, 1.5 and 2 h of artificial insemination (AI). Thirty mares with a dominant follicle > 35 mm in diameter and no bacterial growth or neutrophils detected in uterine smears were inseminated with a total dose of 500 x 10(6) cooled sperm (25 x 10(6) ml(-1) spermatozoa diluted in skim milk) stored at 4 degrees C for 18 to 22 h until use. The mares were slaughtered 0.5 (n = 3), 1 (n = 10) 1.5 (n = 4) or 2 h (n = 13) after AI. The oviducts were separated from the uterus and flushed with phosphate-buffered saline. Spermatozoa were detected in oviduct flushes from 0.5 h onwards after AI and sperm cells were observed in flushes from oviducts in 66.7% of the mares regardless the time of AI. No differences were observed either in the number of sperm cells between the groups or in the number of mares with sperm cells in the oviducts. No differences were observed in the number of mares presenting spermatozoa in the oviduct ipsilateral to the dominant follicle when compared with the contralateral oviduct or in the number of spermatozoa that reached the tubes. Sperm cells were found in the uterus by histological examination in 88.8% of the mares slaughtered 1 h after AI and spermatozoa were located in the uterine glands in 70% of the mares. It can be concluded that sperm cells reach the tube already 0.5 h of insemination. The uterine glands are a possible reservoir for spermatozoa in addition to the oviductal isthmus and the uterotubal junction.