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 eva luated. Vaginal fluid samples were collected in 8 cows at the beginnin g of a natural estrus and then every 8 h for 24 h. Vaginal samples wer e also collected from 208 cows at the time of insemination within 12 t o 24 h interval after the onset of a natural estrus. Time-dependent va riations were registered during the estrus. The limit shear stress for flow production (T-0), the shear stress of equilibrium (T-e) and the consistency index (K) decreased at 8 and 16 h and markedly increased 2 4 h after the beginning of estrus. At the time of insemination, struct ural variation was registered and the fluids were considered to be thi xotropic in samples of 181 cows (87%); in the remaining samples (27 co ws), structural variation was not registered and the fluids were consi dered to be nonthixotropic. For flow behavior values, 178 samples (85. 6%) presented non-Newtonian behavior, while 30 behaved as Newtonian fl uids. The mean values of the T-0 and the T-e were 6.1+/-0.69 and 1.9+/ -0.69 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 rh eological measurements of vaginal fluid at the time of insemination.