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Pattern of blood flow to the bovine uterus was determined by using electromagnetic blood flow probes during the estrous cycle and early pregnancy to evaluate the effect of the early bovine conceptus on uterine blood supply. Pattern of blood flow through the middle uterine artery of pregnant and nonpregnant cows was similar until day 14 after mating or estrus. Between days 14 and 18 of pregnancy, blood flow to the uterine horn containing the conceptus increased two-to-threefold, whereas blood flow to the other uterine horn in these cows remained constant. By day 19 of pregnancy, blood to the pregnant horn had returned to the level on day 13. Blood flow to both uterine horns of pregnant cows was low from days 19 to 25 and then increased to the pregnant horn through the remainder of pregnancy. Uterine blood flow during the estrous cycle of nonpregnant cows was positively associated with systemic concentrations of estradiol, whereas during pregnancy blood flow was positively related with progesterone concentration. These data indicate local control of uterine blood flow by the bovine conceptus, which may function to create optimal conditions for the continuation of pregnancy.