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Chronic exposure of pregnant cows to elevated environmental temperatures results in decreased birth weights of calves. This phenomenon is economically important since reduced birth weights are associated with decreased calf survival and growth. The adverse effects of environmental heat stress on fetal development have been greater than can be explained by a reduction in maternal feed intake or length of gestation.
The rate of uterine blood flow seems to be a primary determinant of nutrient uptake by the gravid (pregnant) uterus, and acute heat stress on days 120 to 130 of gestation has been shown to decrease uterine blood flow in ewes. The effects of chronic heat stress on uterine or umbilical blood flows, however, have not been determined. It has been suggested that chronic heat stress causes a decrease in uterine blood flow, thereby reducing the supply of nutrients available for development of gravid uterine tissues. The objectives of this study were to determine if the adverse effects of chronic environmental heat stress on calf fetal development were related to changes in blood flow and/or nutrient uptake of the gravid uterine tissues.