Sperm distribution in the mare's uterus within 10 h after insemination

Abstract

In a recent study, sperm cells were observed in the uterus by histological examination in 88.8% and 76.9% of the mares slaughtered 1 and 2 h after insemination (AI), respectively, and uterine glands were suggested as a possible reservoir for spermatozoa similarly to the oviductal isthmus and the uterotubal junction. The objective of this study was to verify the sperm distribution in the uterus from 0.5 h until 10 h after AI in the mare. Fifty-three mixed-breed mares in estrus were selected from a population of horses sent to slaughter in an abattoir. Semen was collected from a fertile stallion. Mares with a dominant follicle >35 mm in diameter and no bacterial growth or neutrophils in uterine smears were inseminated with a total dose of 500× 106 cooled sperm (25× 106 mL−1 spermatozoa diluted in skim milk) stored at 4 ◦C for 18–22 h before use. Mares were slaughtered 0.5 h (n= 11), 1 h (n= 11), 2 h (n= 16), 4 h (n= 8), and 10 h (n= 7) after AI; reproductive tracts were recovered within 10 min. The uterus was sectioned and a portion from uterine body and each horn was obtained. The samples were fixed in Bouin’s solution and processed for histological examination. The slides were stained with hematoxylin-eosin and examined under a light microscope. Spermatozoa adjacent to the luminal epithelium and within the uterine glands were searched. Fisher’s Exact Test and the Pearson linear correlation were used in statistical analysis: the number of mares with and without sperm cells in the uterus and in the glands in relation to the time interval between AI and slaughter. Values were considered to be significant at P 0.01) decreased 4 h after AI. The presence of sperm cells in the uterine horn ipsilateral (23/29 mares) to the dominant follicle was similar (P= 0.15) to the numbers observed in the contralateral (18/29 mares) horn. It was concluded that sperm cells are present in uterine glands 30 min after AI. The number of mares with sperm cells in uterine epithelium and glands diminished as the time from AI increased. The sperm distribution is identical in the uterine horns independently to the site of the dominant follicle.