Vaginal Smear for Oestrus Detection in the Bitch

Introduction

Vaginal smears can be used to determine the stage of the oestrous cycle. Smears are generally stained with Leishman's or a Trichrome stain such as Shorr's.

Vaginal Smears

• At the onset of pro-oestrus, large numbers of erythrocytes are present.
• When true oestrus occurs, the number of erythrocytes is reduced, and the smear consists of superficial cells from the stratified squamous epithelium. Such cells include:
  • Anuclear cells
  • Cells with pyknotic nuclei
  • Large intermediate cells
• Towards the end of oestrus, polymorphonuclear neutrophil leukocytes appear. These become the dominant cell type during metoestrus.
• In anoestrus,different cell types are present,these are:
  • Nucleated basal of the stratified squamous epithelium
  • Intermediate cells of the stratified squamous epithelium
  • Few neutrophils

Cell Type	Para Basal	Small Intermediate	Large Intermediate	Anuclear Keratinised	Red Blood	Neutrophils
Early Pro-Oestrus	+++	+++	+-	-	+	+
Late Pro-Oestrus	+	++	++	++	+++	-
Early Oestrus	-	-	+++	++++	++	-
Late Oestrus	-	-	+++	+++	-	+
Ealy Metoestrus	-	+	-	+-	-	+++
Anoestrus	++	+	-	-	+-	+
Vaginitis/Pyometra	+-	+-	+-	-	+-	++++

Vaginal Epithelium

• Anoestrous: low columnar-cuboidal, comprises of 2-3 layers.
• Pro-oestrus: high stratified squamous persists until late stages of oestrus.
• Stratum corneum and the layers immediately beneath it are lost by desquamation during pro-oestrus and oestrus. This leaves low squamous epithelium, which becomes converted to columnar epithelium 1-3 weeks after the end of oestrus.
• Metoestrus and pregnancy: high columnar, higher than during anoestrus.
• During pro-oestrus, oestrus and early metoestrus, the epithelium and lamina propria are infiltrated with large numbers of neutrophils, which eventually escape into the vaginal lumen.