Rheological behavior of the vaginal fluid of dairy cows at estrus

The present study was conducted to evaluate rheological properties of the vaginal fluid in dairy cows. Thixotropy and flow behavior were evaluated. Vaginal fluid samples were collected in 8 cows at the beginning of a natural estrus and then every 8 h for 24 h. Vaginal samples were also collected from 208 cows at the time of insemination within 12 to 24 h interval after the onset of a natural estrus. Time-dependent variations were registered during the estrus. The limit shear stress for flow production (T(o)), the shear stress of equilibrium (T(e)) and the consistency index (K) decreased at 8 and 16 h and markedly increased 24 h after the beginning of estrus. At the time of insemination, structural variation was registered and the fluids were considered to be thixotropic in samples of 181 cows (87%); in the remaining samples (27 cows), structural variation was not registered and the fluids were considered to be nonthixotropic. For flow behavior values, 178 samples (85.6%) presented non-Newtonian behavior, while 30 behaved as Newtonian fluids. The mean values of the T(o) and the T(e) were 6.1 ± 0.69 and 19 ± 06.9 pascals, respectively. Consistency index (K) mean was 364.9 ± 41.4 milipascals per second(n). Our data show an increase of fluidity at the middle of the estrus period in the cow and a wide variation of theological measurements of vaginal fluid at the time of insemination.