Page 969 - Small Animal Internal Medicine, 6th Edition

CHAPTER 54 The Practice of Theriogenology 941

hormone testing during proestrus—when vaginal cytology to 60% immature (parabasal and intermediate) cells over a
is primarily parabasal and intermediate cells—is costly and 24- to 36-hour period, accompanied by neutrophils. If
VetBooks.ir not contributory to actual ovulation timing. vaginal cytologic examination is performed until the dies-
Competence in vaginal cytologic analysis should be
trual shift is observed, a retrospective analysis of the date of
acquired by any clinician offering reproductive services,
because commercial laboratory interpretation of serial cytol- the LH surge (7-10 days previously), ovulation and ova
ogies is costly and not timely. Proper technique is important
to obtain cells representative of the hormonal changes occur-
ring. The sample should be collected from the cranial vagina,
because cells from the clitoral fossa, vestibule, urethral
papilla, or vestibulovaginal junction are not as indicative of
the stage of the cycle (Figs. 54.11 and 54.12). The vaginal
cytology swab should be rolled onto a slide without overlap
or smearing (Fig. 54.13). Under the influence of increased
estrogen levels, the number of layers making up the vaginal
epithelium increases dramatically, presumably to provide
protection to the mucosa during copulation. As estrogen
rises during proestrus, the maturation rate of the epithelial
cells increases, as does the number of keratinized cornified
epithelial (“superficial”) cells seen on a vaginal smear. Full
cornification continues throughout estrus until the diestrual
shift occurs, signifying the first day of diestrus. The vaginal
smear then changes abruptly from full cornification to 40%

Vagina
Vestibule

Clitoral
fossa

FIG 54.11 FIG 54.13
Schematic showing the anatomic orientation of the vestibule Rolling the vaginal swab onto a slide results in a single
and vagina of the bitch. layer of cells to stain and evaluate.

FIG 54.12
Schematic illustrating proper placement of the cotton-tipped swab for vaginal cytology.