a1 Roman L. Hruska U.S. Meat Animal Research Center, U.S.D.A., Clay Center, NE, U.S.A. 68933
a2 Department of Animal Science, Iowa State University, Ames, I A, U.S.A. 50011
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 (O2), 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.
(Received July 03 1984)