Uterine blood flow during the first 3 weeks of pregnancy in dairy cows.

Transrectal color Doppler sonography was used to compare changes in uterine blood flow between cyclic and early pregnant lactating dairy cows. Examinations were carried out in 53 multiparous lactating cows on days 3, 6, 9, 11, 13, 15, 18 and 21 (day 0=estrus). Fourteen cows were examined during the estrous cycle and thirty-nine cows after insemination with frozen/thawed sperm. Uterine blood flow was reflected by the time-averaged maximum velocity (TAMV) and the pulsatility index (PI) in the uterine artery ipsilateral to the corpus luteum. Twenty-one cows that were not pregnant on day 25 were excluded from the study. There was high inter-individual variability in PI- (CV: 22-62%) and TAMV-values (CV: 22-42%) at all examinations. In cyclic cows, TAMV values increased between days 13 and 18 and PI values decreased between days 15 and 21 (P<0.05). In pregnant cows (n=18), TAMV values increased from days 9 to 11 and then decreased to minimal values by day 18 (P<0.05). The PI values decreased between days 3 and 11 and then increased to maximum levels on day 18 (P<0.05). On day 21, both variables reached (P<0.05) values that did not differ (P>0.05) from those on day 11. The changes in TAMV were correlated with estrogen and progesterone concentrations (r=0.69 and -0.70, respectively; P<0.05) in cycling cows, but not in pregnant cows (P>0.05). The PI values did not correlate with steroid hormone levels (P>0.05). Differences in uterine blood flow between cycling and early pregnant cows were observed only on day 18 (P<0.05). The results show that in pregnant cows changes in uterine blood supply can be detected already in the second week after insemination; these changes do not occur in the second week of the cycle.