Thermal Stress Effects on Uterine Blood Flow in Dairy Cows

Abstract

Three ovariectomized dairy cows, fitted with blood flow transducers around a mid-uterine artery, were assigned to an experiment of simple reversal design to determine the effects of thermal stress (shade or no shade) on the increased uterine blood flow (UBF) after intravenous injection of estradiol-17/β (200 μg). Resultant increases in UBF after estradiol were evaluated both as absolute changes (ml/min) and percentage change. Tests for heterogeneity of regression established that treatment response curves for both absolute and percentage changes in UBF were not parallel. Rate of increase in UBF was greater and the peaks higher in cows subjected to shade (n=7) than those in no shade (n=7; P<.0]). Cows subjected to shade had an overall 17.4% greater absolute change (128 vs 109 ml/min) and a 43.6% greater change (412 vs 287%) in UBF than cows in no shade. Uterine blood flow appears to be significantly affected by thermal stress when tested under practical farm conditions in which environmental modification with shade is known to improve conception rates. Copyright © 1978. American Society of Animal Science . Copyright 1978 by American Society of Animal Science.