A quantitative morphological study of the bovine vaginal epithelium during the oestrous cycle.

Samples were collected post mortem from 28 cycling parous cows. At all stages of the oestrous cycle, the cranial vaginal epithelium was thinner (P less than 0.001), had fewer cell layers (P less than 0.001) and proportionally more superficial columnar cells (P less than 0.001) than more caudal regions. At all stages of the cycle there were more intraepithelial lymphocytes caudally than in more cranial regions (P less than 0.001). At oestrus the proportion of superficial columnar cells was maximal, having increased from the late dioestrus proportions of 1, 29 and 40 per cent of all superficial cells to 15, 54 and 83 per cent in caudal, middle and cranial regions, respectively (P less than 0.02). However, the epithelial thickness in all regions of the vagina was greatest at metoestrus (P less than 0.02). At this stage, the number of cell layers was greater than at any other stage (P less than 0.05).