Improved method for vaginal plug detection in rats

Abstract

Time mating of rodents is essential in many experimental procedures. The presence of the vaginal plug is frequently used as an indicator to confirm that mating has occurred. In rats, vaginal plugs are often deep and therefore difficult to detect by
vulvar inspection. This study was carried out to assess the applicability of a human otoscope for detection of deep plugs, and the predictive value of plugs for pregnancy. A total of 132 Wistar female rats in proestrous were mated and examined
for vaginal plugs on the next morning with an otoscope. All the plugs were located deep inside the vagina and could not be seen without the scope. The pregnancy rate of all females in proestrous was 69.7 %. Of all females, 72.7% had a vaginal plug and the positive predictive value of plug detection was 91.7 %. The sensitivity of the vaginal plug method was 95.7 % and specificity 80.0%. In conclusion, this study shows that detection of plugs has value for predicting pregnancies in rats. The method devised is quick, straightforward and painless to the animals and it is easily taught to technicians.