In canine estrus cytology, which cell type predominates?

• A. Parabasal cells
• B. Glandular cells
• C. Basal cells
• D. Cornified epithelium

Answer: (D)

In canine estrus cytology, cornified epithelium predominates. Estrogen drives keratinization of the vaginal epithelium, so the smear is filled with large, flat, squamous cells that are often anucleate or have only pyknotic nuclei and dense cytoplasm. Neutrophils are minimal at this stage, helping distinguish it from proestrus, where nucleated epithelial cells and many neutrophils are common. Parabasal and basal cells appear more in proestrus or anestrus, not during estrus, and glandular cells are not the characteristic finding of this phase. Seeing mostly cornified cells on the smear indicates the animal is in estrus.