Watch Now: Join Dr. Marty Greer, Revival’s Director of Veterinary Services, as she explains how to use vaginal cytology to accurately time breeding in dogs. This educational webinar walks you through one of the most effective tools for predicting ovulation and increasing your chances of successful conception.

In this video, you’ll learn:

• How to properly collect vaginal cytology samples

• How to interpret canine cytology slides

• When and why to combine cytology with progesterone testing

• Practical tips for improving breeding outcomes

Perfect for breeders and veterinary professionals, this guide helps you confidently navigate the canine fertility cycle and make informed decisions to support reproductive success. Watch Now!

View Dr. Greer’s Canine Vaginal Cytology Handout

*This is just a brief overview—watch the full webinar for all the in-depth details of canine vaginal cytology!

Vaginal Cytology in Dogs: A Practical Tool for Breeding Success

There are two key reasons to learn how to perform vaginal cytology—either yourself or with your veterinarian’s help. First, it helps determine the right time to begin progesterone testing. Many breeders may end up running unnecessary progesterone tests, which can be costly whether done in-house or at a clinic. Second, cytology allows you to identify any abnormal pathology in the female reproductive tract, giving you the chance to catch issues early and intervene as needed.

Vaginal cytology plays an important role and should not be replaced by progesterone testing—it should complement it. Quantitative progesterone testing remains essential for precision breeding, especially in high-risk pregnancies, planned C-sections, and when using fresh chilled or frozen semen. A high-risk pregnancy might involve a singleton pup, a very large litter, or complications like illness, trauma, or resorption. Knowing exact due dates in these cases is critical for timing medical interventions and improving outcomes.

Essential Tools and Techniques for Canine Vaginal Cytology

To perform a vaginal cytology, use a long-handled swab or cytology brush inserted upward at a 45-degree angle to match the natural angle of the vaginal tract. Avoid short cotton swabs, which can’t reach far enough. Once inserted, gently rotate to collect cells, then roll—not smear—the swab across a slide to preserve cell structure.

After air-drying the slide, use a three-step staining process, dipping in each solution to fix and stain the cells. You don’t need to use a new stain set each time you perform a vaginal cytology—reusing the same stain dip multiple times is perfectly fine and helps ensure consistent, even staining for clear cell evaluation under the microscope. Be sure to label the front of the slide and rinse the back only to avoid washing off the sample. A microscope, stain kit, swabs, and slides are all that’s needed to get started. Choose a microscope with a built-in light source—much easier than the old method of angling a mirror just right. Opt for a binocular model, which allows you to use both eyes comfortably. Monocular scopes require closing one eye, which can be tiring and less efficient. For vaginal cytology, make sure the microscope offers at least 40x and 100x magnification.

Vaginal cytology is a useful, affordable tool that works well with progesterone testing and behavioral cues for breeding timing. It’s especially helpful in assessing whether ovulation has occurred or if a cycle is abnormal (like a split heat). Breeders can improve success rates and reduce unnecessary progesterone tests by using cytology to guide timing. While not a replacement for quantitative progesterone testing—especially in high-risk or surgical breedings—cytology adds valuable context and insight when planning matings or monitoring reproductive health.

Understanding Split Heats in Dogs

Split heats occur when a female dog begins a heat cycle but does not ovulate, resulting in an incomplete cycle that may restart weeks later.

Performing vaginal cytology on a dog with a split heat is done the same way as with a regular cycle—the collection and staining process remains unchanged, but the slide may show delayed or incomplete cornification. In cases of split heats, vaginal cytology often shows a brief rise in cornified cells that then regress back to non-cornified, or it may never reach full cornification at all. These misleading cycles can appear as though the dog is entering heat, only to abruptly stall—highlighting why not every reproductive cycle follows the textbook.

Split heats are more commonly observed in certain breeds, particularly northern breeds like Samoyeds, Finnish Lapphunds, Alaskan Malamutes, and Siberian Huskies. However, they can occur in any breed. If a female exhibits signs of being in heat but never progresses to ovulation or full cytologic maturity, it may indicate a split cycle.

For future breedings, especially in females known to have late or split ovulations, a combination of vaginal cytology and progesterone testing can help reduce the number of hormone draws. Using cytology to monitor progression before initiating progesterone testing may help breeders time testing more effectively and avoid unnecessary draws.

For more personalized guidance on canine reproduction or for help in selecting the supplies you’ll need for canine vaginal cytology, call our Animal Care Specialists at 800.786.4751.