THE RELATIONSHIP OF RHEOLOGICAL BEHAVIOR OF THE VAGINAL FLUID AT THE TIME OF INSEMINATION TO THE PREGNANCY RATE IN DAIRY-COWS

The objective of this study was to determine whether rheological prope rties of the vaginal fluid at the time of insemination could be used a s an indicator of potential fertility in dairy cows. Thixotropy and fl ow behavior were evaluated. Vaginal samples were collected from 347 co ws at the time of insemination, within a 12- to 24-h interval after th e onset of a natural estrus. Logistic regression analysis showed no si gnificant effects of thixotropy measurements on the pregnancy rate, wh ile flow behavior and the index of consistency (K) had a significant e ffect.The decrease in the consistency index (K) was related to the inc rease in the pregnancy rate (odds ratio=0.99; P=0.014), and the risk o f nonpregnancy was higher (odds ratio=0.46; P=0.024) in cows in which vaginal fluid had a Newtonian behavior. Non-Newtonian behavior was rec orded in 294 samples (85%) while 53 behaved as Newtonian fluids. For s amples from all cows, the mean value of the consistency index was 310 +/- 28.2 milliPascals.second(n) (x +/- SEM) and ranged from 0 to 3881 milliPascals.second(n). In Newtonian samples, the consistency index me an was 2.6 +/- 0.6 milliPascals.second(n) and 367.6 +/- 30.4 milliPasc als.second(n) for non-Newtonian samples. Of the 347 cows, 131 (38%) be came pregnant. For flow behavior classification, 15 (28.3%) cows in wh ich samples had Newtonian behavior and 116 (39.5%) cows with non-Newto nian samples became pregnant. Therefore, the highest probability of pr egnancy was shown by cows in which samples had non-Newtonian behavior and the lowest consistency index values. Our data suggest that flow be havior measurements of the vaginal fluid at the time of insemination m ay be an indicator of potential fertility in cattle. (C) 1997 by Elsev ier Science Inc.