Final answer:
Proestrus stage of estrus has a high number of erythrocytes and basal and parabasal epithelial cells.
Step-by-step explanation:
The stage of estrus that has a high number of erythrocytes and basal and parabasal epithelial cells is Proestrus.
During proestrus, the lining of the uterus, called the endometrium, is preparing for potential implantation. This is characterized by an increase in the number of erythrocytes (red blood cells) and basal and parabasal epithelial cells in the vaginal smear.
In contrast, during other stages like estrus, metestrus, and anestrus, the number of erythrocytes and basal and parabasal epithelial cells may decrease or remain stable.