Overview of Reproductive Diseases of the Female Small Animal

A clean, cotton tip swab is commonly used to swab the vagina to obtain a cytology sample. An endoscope cone or vaginal speculum can be used to guide the swab. A right-handed person can hold the bitch’s vulva with a gloved left hand, opening the vulvar lips with the thumb and middle finger, while using the index finger behind the vulva to support it. The swab is moistened with warm tap water and inserted almost vertically into the vagina, avoiding the clitoral area, up and over the brim of the pelvis. It may be helpful to forward the swab, especially in small size bitches and bitches without serosanguineous discharge. If the swab feels "stuck" in the vaginal folds, it may be pulled back slightly and redirected before proceeding. Once the swab is inserted to a depth of at least 6–10 cm (2–4 in.), it is rolled a few times in one direction (if rotated back and forth, the cotton may unroll and drop in the vagina) and withdrawn. Inserting the swab as deep as possible to reach the cranial part of the vagina (versus the caudal part) minimizes collection of extraneous debris. Getting in a habit of reaching the cranial vagina is also helpful to take samples for vaginal culture and for AI. The swab is rolled on a clean microscope slide, air-dried, and stained; two slides are recommended. Stains that can be used include Wright-Giemsa, Romanowsky, methylene blue, eosin-nigrosin, Gram stain, etc. The slides with smears are dipped 5–7 times in each jar, rinsed with tap water, air-dried, and examined under the microscope. Viewing under 200X magnification first is helpful to get an overall impression of the types and distribution of cells before examining more closely under 400X magnification.

Various theriogenologists, clinical pathologists, and other practitioners have interpreted vaginal cytology of the bitch a little differently. One method is described here. The vaginal mucosa is responsive primarily to estrogens, and so vaginal cytology is useful only during the estrogenic phase of the cycle. Parabasal cells are small, round cells with large and distinct nuclei. The total area of the cytoplasm part of the cell is smaller than the nucleus. These cells (along with RBCs) are present during proestrus. Superficial intermediate cells are larger than the parabasal cells, with small nuclei and irregular/folded borders. Large numbers of these cells are seen during late proestrus to early estrus. Superficial cells, also called cornified or anucleated, are the largest of the epithelial cells present during estrus. Under a simple microscope, the nuclei of these cells appear faded or absent. The cells also appear "light in weight," multi-layered, and with folded borders. The appearance of 80%–90% of these cells in the smear is used to indicate that breeding can start. A series of vaginal cytology samples is needed to observe the progressive change in epithelial cells; only one smear is unreliable. Epithelial cells may remain the same for many days in some bitches, whereas they may change within 24 hr in others. In addition, many bitches reach 80%–90% cornification during estrus, but in others cornification never goes above 70%. In these bitches, waiting for 80%–90% cornification will result in loss of breeding during that cycle. Another breeding management tool is the progesterone assay, discussed below. The appearance of neutrophils on the vaginal cytology sample indicates the first day of diestrus, and whelping will occur 57–58 days later. Daily vaginal cytology samples are recommended because in some bitches, the cells change from cornified to superficial intermediate and neutrophils appear within 24 hours.