Estrus detection by using vaginal cytologic examination in miniature swine

Vaginal smears were obtained from four Yucatan miniature swine daily for 69 days and stained with hematologic stain. Epithelial cells were categorized as superficial, large intermediate, small intermediate, or parabasal. Leukocytes were also quantitated. External signs of estrus were recorded, including swelling, discharge, restlessness, or vocalization. Mean age of three of the swine was 147 days at the beginning of the study. The fourth pig was 317 days old. The three younger swine had their first observed estrus at the age of 178 days (range, 167 to 196 days). Mean cycle length was 17 to 21 days. The moving mean leukocyte count (i.e., each value was averaged with the values for the previous day and the following day) always exceeded the epithelial cell count (regardless of type), except during the 3 to 4 days when the pigs exhibited external signs of estrus. Further, epithelial cells were at their peak during estrus, decreasing markedly during diestrus, and increasing again during proestrus. The combined superficial plus large intermediate cell counts were significantly higher during estrus than during diestrus or proestrus. We conclude that daily vaginal smears can be used to determine the stage of estrus in Yucatan pigs.