Effects of chronic environmental heat stress on blood flow and nutrient uptake of the gravid bovine uterus and foetus

Summary To evaluate the effects of chronic environmental heat stress during mid-gestation on gravid uterine and foetal metabolism, mature Hereford cows were assigned to control ( n = 8) or heat stress ( n = 5) treatments beginning on day 100 of gestation. Uterine and umbilical blood flows were estimated by the steady-state diffusion procedure on day 169 ± 4 of gestation. Oxygen (O 2 ), glucose, lactate, α-amino nitrogen and urea nitrogen concentrations were determined for uterine and umbilical blood samples collected during this procedure. Foetuses and foetal fluids were collected on day 174±4. Uterine and umbilical blood flows were reduced and foetal weight also was less for heat-stressed than for control cows. In addition, foetal liver weight as a proportion of foetal weight and total foetal liver RNA and protein were less for heat-stressed cows. Uterine and umbilical arterial–venous concentration differences in metabolites were similar between the two groups. Uterine, foetal and utero-placental uptake or secretion rates of the metabolites measured in this study were reduced in the heat-stressed cows, primarily because of differences in blood flow. Thus, chronic heat stress during mid-gestation had an adverse effect on foetal development resulting, at least in part, from decreased uterine and umbilical blood flows, which led to a reduction in uterine, utero-placental and foetal nutrient uptake or secretion rates.