Shrinkage in the horizontal dimensions of the vulva (vulvar shrinkage) as an indicator of standing heat in the beagle

During the proestrous and estrous periods in 12 beagles, the following para meters were measured daily: the horizontal dimensions of the vulva, vaginal cytology, and serum luteinizing hormone (LH) and progesterone concentratio ns. Measurements of serum LH concentrations allowed for the identification of the LH surge and the optimal time for artificial insemination (Al). Nine out of the 12 beagles became pregnant through Al and completed a gestation . Shrinkage in the horizontal dimensions of the vulva (i.e., vulvar shrinka ge) was primarily observed prior and subsequent to the LH surge. In six of the nine (66.7%) beagles that became pregnant, vulvar shrinkage was observe d on the days in which the LH surge was confirmed, and the rate of vulvar s hrinkage tended to be greater at higher serum LH concentrations. Further vu lvar shrinkage was identified in all nine beagles within two days of the LH surge. An increase in the serum progesterone concentration was observed af ter the LH surge in each of the beagles that became pregnant, together with clinical signs of estrous behavior (i.e., standing heat) as well as a chan ge in vulva condition from swollen to soft. This demonstrates that vulvar s hrinkage is induced in response to the onset of the LH surge and that the L H surge can be predicted through the measurement of the horizontal dimensio ns of the vulva, vaginal cytology, and the assessment of serum progesterone concentrations in beagles.