Prediction of breeding time using vaginal cytology in canine reproduction

Prediction of breeding time using vaginal cytology in canine reproduction

^1*L. Kipjen Singh, ²K. Merina Devi, ³Anup Kumar singh and ⁴M.K Patra

¹PhD Scholar, Division of Animal Reproduction, Gynaecology and Obstetrics, National Dairy Research Institute, Karnal;  ²Assistant professor, Department of Livestock Farm Complex, COVSc & A.H, CAU, Jalukie, Nagaland; ³Phd Scholar, Livestock Production and Management National Dairy Research Institute, Karnal; ⁴Scientist(ss),Animal Reproduction Division, ICAR-Indian Veterinary Research Institute, Izatnagar, U.P

Introduction

Vaginal cytology is one of the simple useful clinical laboratory techniques that give rapid results in canine reproduction. The stages of the canine estrous cycle are proestrus, estrus, diestrus and anestrus. The physical signs of estrus incudes vulvar swelling, vaginal bleeding (proestrus) etc. may not indicate the stage of the estrous cycle as some bitches bleed very little and others show bleeding through estrus and sometimes into diestrus. Moreover, the receptivity of female to a male during estrus varies among the bitches. Thus, the cytological changes from vaginal smears that reflect the underlying endocrine events of the cycle are considered as a better predictor of the breeding time.

Principle of vaginal cytology

It is based on the determination of cyclic cellular changes occurring in the vaginal epithelium as a result of reproductive hormone levels, especially estrogen.

Procedure of sample collection and preparation of slide

• Moisten a cotton swab with few drops of sterile saline. Open the vulvar lips, pull the vulva dorsally, insert the swab into the caudal vagina and twist a full turn to pick up small cells.
• Prepare the smear immediately after the withdrawal of the swab by rolling (not sliding or rubbing) the cotton tip along the length of a glass microscope slide. In general, two parallel tracks can be rolled on a single slide.
• Fix the smear slide in methanol for 5-7 minutes. The slide is then allowed to dry fully and remain unfixed for up to a few hours.
• Slides can be stained with new Methylene blue stain, DifQuik stain, Wright stain, Wright’s Giemsa stain
• Stain the slides using diluted Giemsa solution (1:20 with distilled water) for 45 minutes.
• Rinse the stained slide with distilled water and allowed to air dry for a few minutes.
• Read the slide first under low power to determine the cellularity and cell types trend. Move to a higher power to establish cell types. View several fields to get an overall visual idea of the percentage of cornified cells.

Examination of vaginal smears:

1. a) Non-cornified

• Parabasal cells are small round or ovoid cells having a large nucleus to cytoplasm ratio.
• Intermediate cells have a smaller nucleus and more cytoplasm. They are larger than parabasal cells.

1. b) Cornified

• Superficial cells are the largest cell with a small pyknotic nucleus and angular cytoplasm. The cells have sharp, flat and angular cytoplasm.
• Anuclear cells have no visible nucleus and angular cytoplasm.

courtesy: http://therio.vetmed.lsu.edu/k-9__vaginal_cytology.htm

Determination of fertile time for breeding or artificial insemination

In anestrus and diestrus where there is no estrogen, the vaginal wall becomes very thin and the cell will appear as non-cornified cells. The level of estrogen will start rising during proestrus and the vaginal epithelium will become hyperplastic and more cornified. The cornified cells increase by about 10% per day until above 80% cornification during estrus. During estrus, the vaginal epithelium becomes very thick and cornification of the cell goes above 80%. The stage where vaginal epithelium of above 80% cornified cells seen is regarded as the breeding time. The PMNs (polymorphonuclear cells) do not cross the epithelium and makes the background look very clean in the estrus stage. On the first day of diestrus, the vaginal cells abruptly change to around 50% non-cornified cells. The day from which the smear changes from 100% cornified cells to 50% non-cornified cells is denoted as the first day of cytologic diestrus.

Pattern of cytological vaginal smears during the estrous cycle

Conclusion

In conclusion, the difficulties associated with the detection of estrus in a female dog are simplified with the advent of vaginal cytology. Therefore, this method of estrus detection not only helps the veterinarian but also the pet owner as a whole for the accurate time of estrus and subsequent breeding.

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