Abstract: The purpose of this study was to investigate the changes in histological structure and the expression of lactoferrin (LF) in the uterus and ovaries of dogs during the normal estrus and with pyometra. Masson’s, VVG and PAS histochemical staining were used to observe the histological characteristics of uteruses and ovaries in anestrus, estrus, and pyometra. The immunohistochemical SP method was used to observe the distribution of LF. The results showed that the endometrium/myometrium ratios in the period of anestrus and estrus were 0.762 0 and 0.924 3, respectively. The content of collagen fibers in the uterine lamina propria in anestrus was higher than that in estrus, and the collagen fibers content of ovary in estrus was higher than that in anestrus. The internal elastic membranes of uterine vascular layer and ovarian blood vessels were clear and intact in anestrus and estrus. During the period of anestrus, the superficial lumen was small and the deep lumen was large, the epithelium of glandular duct was consisted of the single layered columnar epitheliums, and the PAS positive reaction was strong in epithelial cells and glandular cavity. During the period of estrus, the glandular lumen became larger, the glandular epithelium was the single layered cuboidal epithelium, and PAS positive reaction was found in the epithelial cells and glandular lumen. The endometrial epithelium was monolayer columnar epithelium in both estrus and anestrus periods, but the position of the nucleus was different. The endometrial epithelium nucleus of anestrus period was located in the center of cell, the endometrial epithelium nucleus of estrus period was at the top of cell. When the dogs have pyometra, the endometrium/myometrium ratio was 1.615 0, the content of collagen fibers in the lamina propria of uteruses and ovaries was less than that during normal estrus, the glandular lumen was large and irregular in shape, the inflammatory cells infiltrated in the lumen, the glandular epithelium was the single layered cuboidal epithelium, the lymphocytes were located in the basement membrane, and PAS positive reaction was weak in epithelial cells and lumen; the elastic membrane in uterine vascular layer and ovarian blood vessels became thinner and fractured compared during normal estrus; the endometrial epithelium was the single monolayer columnar epithelium, and the nucleus was located at basal plasma membrane. The expression level of LF in uterine glandular epithelium and ovaries in anestrus stage was higher than that in estrus period, and the expression level of LF in endometrial epithelium in estrus was higher than that in anestrus. The expression of LF in uteruses and ovaries of dogs with pyometra was lower. The results suggested that the histological characteristics of uteruses and ovaries of dogs in normal estrus and pyometra were significantly different, and the expression level of LF was also different.

Key words: normal estrous stages, pyometra, dog uterus and ovary, histological structure, lactoferrin