To investigate the change of vaginal epithelial cell in estrus-induced Shih-tzu bitch, estrus was induced by PMSG (50 IU/kg, for 10 days) and hCG (1,000 IU, on Day 10) in 12 anestrus Shih-tzu bitches. Day-changes of vaginal epithelial cells during the whole period of hormone treatment were investigated in each experimental bitches. The first day of vulvar bleeding and the first day of male acceptant was on $6.72{pm}1.38$ days ($Mean{pm}S.D.$), and $10.44{pm}1.63$ days after the first PMSG treatment. The duration of proestrus and estrus was $4.36{pm}1.20$ days, and $7.58{pm}1.43$ days. Characteristic features of vaginal cytology during the estrous cycle were the high proportion of large intermediate cell, superficial cell, anuclear cell and erythrocyte in proestrus, superficial cell and anuclear cell in estrus, and parabasal cell, small and large intermediate cell, and leukocyte in diestrus, respectively. When it was timed from the first day of PMSG administration (Day 0), the cornification index (CI) was the high proportion in proestrus and estrus. The CI peak was maintained above 80% between Day 11~14 (4 days) and CI showed a peak at Day 12. These results indicated that the 12 Shih-tzu bitches showed positive estrus induction by vaginal smear test and observation of clinical estrus sign.

Keywords: vaginal cytology, estrus induction, estrous cycle, Shih-tzu