[Microscopic structure of the uterine mucosa in cows during the estrus cycle].

The endometrium of a cow shows little variation during the sexual cycle. Proliferation starts by increasing the relative volume of the connective-tissue layer of mucous membrane at the onset of pro-oestrus and culminates during oestrus. The volume of luminal epithelium increases more slowly from the lowest values in di-oestrus, the maximum level being obtained in met-oestrus. The volume of glandular epithelium is greatest in met-oestrus and at the start of di-oestrus; during pro-oestrus it is low but increases rapidly afterwards. The nuclei of luminal and gland cells are located basally and are shifted towards the centre of cells in the period of secretory activity. The nucleocytoplasmic ratio of epithelium cells is at its maximum during pro-oestrus and decreases in the subsequent stages. The intensity of PAS reaction also increases at the onset of pro-oestrus, the maximum being obtained in met-oestrus, to persist also in di-oestrus in some cells. Lipid droplets occur, on a larger scale, in gland cells, and the frequency of their occurrence increases in met-oestrus and di-oestrus.