Basis of cytology

The Pap smear is an inexpensive method and exact point of the estrous cycle in the bitch is. Despite the great advantages in the female reproductive management must be complemented with more sensitive the day of ovulation as quantitative or qualitative assessment of progesterone analysis.

Cytology is the evaluation of vaginal cells by determining its type and amount. The morphology of the epithelial cells of the vagina varies during the estrous cycle and is produced by the action of hormones that regulate the cycle.

At the beginning of the estrous cycle the cells are very close to the blood flow, with increasing estrogen vaginal wall thickens cells so they separate blood supply leading to cellular transformation.

Obtaining the Sample

The objective is to obtain a sample of epithelial cells from the vagina, and one should avoid sampling from the vestibule (i.e. just inside the vulva). Even in small dogs, the swab should be inserted several inches past the vulva; in large breed dogs (e.g. German Shepard bitch), a majority of the 6-inch swab can be inserted. Bitches in proestrus or estrus rarely object to this procedure, although some restraint may be required to prevent “squirming”.

Part the lips of the vulva and gently insert a swab at a relatively steep angle. Some people suggest using a speculum (e.g. the cone from an otoscope) and some like to moisten the swab with saline prior to use, but neither of these is critical. After 1-2 inches of the swab have been inserted, the angle of insertion can be altered to roughly 45 degrees and insertion continued.

When the swab is fully inserted, rotate the end through 2-3 revolutions, which will allow the cotton tip to pick up an adequate load of cells. The swab can then be gently withdrawn. Prepare the smear immediately after withdrawal of the swab by rolling (not sliding or rubbing) the cotton tip along the length of a glass microscope slide. Generally, two parallel tracks can be rolled on a single slide.

As soon as the smear is prepared, dip it 5 to 10 times in a container of methanol, or fix by use of a spray fixative. It is best to fix expeditiously, but allowing the slide to dry fully and remain unfixed for up to a few hours is generally not a problem. After fixation, the slide can be stored for prolonged periods of time, although typically, it is stained without delay.

Diff-Quik is a very convenient stain for use with vaginal smears. It consists of two solutions: an eosinophilic (red) solution and a basophilic (blue) stain. It is best to have a small container of each component and replace the stains with some regularity, as they will become contaminated with vaginal cells after staining a number of slides. To stain the smear, dip the slide in and out of the red stain 5 to 10 times, the in and out of the blue stain 5 to 10 times.

After dipping in the blue stain, rinse the slide in tap water and it’s ready to examine. Examine while still wet or dry the slide and apply a coverslip.

The interpretation of the sample was performed according to the prevalence of the different cell types, which is indicative of hormonal status of the female. Do not forget that the interpretation of the Pap smear should be the result of monitoring the evolution of the cell type, because a single sample may be compatible with different stages of the estrous cycle.

Referrals: Anyone can make an assessment of the estrous cycle using a microscope and with a little practice. In case of not wanting to spend big money on a microscope, we recommend the model Microscope with monitor whose low price, high optical performance and light weight make it an ideal tool for breeders or veterinarians who want to follow anywhere.