Acute Synergistic Effects of AIr Temperature, Humidity, and Velocity on Homeostasis of Marketsize Broilers

Core body temperature (tb) of marketsize male broilers (46 .3 d; 2.8 .0.1 kg; Ross . Ross breed) wascontinuously measured by telemetry during acute, 90 to 240min exposures to 18 thermally challenging conditions. Thethermal conditions consisted of 18 factorial combinations of three drybulb air temperatures (tdb; 35.C, 38.C, and 41.C),two dewpoint temperatures (tdp; 19.4.C and 26.1.C), and three air velocities (V; 0.2, 0.7, and 1.2 m s1). Based on tb riseafter 90min exposures to the thermal conditions, a temperaturehumidityvelocity index (THVI) was developed to delineatethe synergistic effects of the thermal components on the birds, having the form of THVI = (0.85tdb + 0.15twb) . V0.058, wheretwb = wetbulb temperature. The homeostasis state of the bird was classified as normal, alert, danger, or emergency, whichcorrespond to a tb rise threshold of 1.0.C, 2.5.C, 4.0.C, or >4.0.C, respectively. These different homeostasis states werefunctionally and graphically expressed in terms of THVI and exposure time. For example, if the broilers were acutely exposedto a thermal condition for 90 min, then the THVI threshold for the normal, alert, danger, and emergency state would be about35.C, 38.C, 40.C, and >40.C, respectively. If the exposure duration was increased to 120 min, the THVI threshold woulddrop to 34.C, 37.C, 38.C, and >38.C, respectively. The results of this study serve as a scientific basis for makingmanagement decisions and risk assessment associated with marketsize broiler production and handling under thermallychallenging conditions.