Vaginal Smear for Oestrus Detection in the Bitch

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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.