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Core body temperature (t b ) of market-size male broilers (46 ± 3 d; 2.8 ± 0.1 kg; Ross × Ross breed) was continuously measured by telemetry during acute, 90- to 240-min exposures to 18 thermally challenging conditions. The thermal conditions consisted of 18 factorial combinations of three dry-bulb air temperatures (t db ; 35°C, 38°C, and 41°C), two dewpoint temperatures (t dp ; 19.4°C and 26.1°C), and three air velocities (V; 0.2, 0.7, and 1.2 m s -1 ). Based on t b rise after 90-min exposures to the thermal conditions, a temperature-humidity-velocity index (THVI) was developed to delineate the synergistic effects of the thermal components on the birds, having the form of THVI = (0.85t db + 0.15t wb ) × V -0.058 , where t wb = wet-bulb temperature. The homeostasis state of the bird was classified as normal, alert, danger, or emergency, which correspond to a t b rise threshold of 1.0°C, 2.5°C, 4.0°C, or > 4.0°C, respectively. These different homeostasis states were functionally and graphically expressed in terms of THVI and exposure time. For example, if the broilers were acutely exposed to a thermal condition for 90 min, then the THVI threshold for the normal, alert, danger, and emergency state would be about 35°C, 38°C, 40°C, and >40°C, respectively. If the exposure duration was increased to 120 min, the THVI threshold would drop to 34°C, 37°C, 38°C, and >38°C, respectively. The results of this study serve as a scientific basis for making management decisions and risk assessment associated with market-size broiler production and handling under thermally challenging conditions.


Journal Paper No. J–19898 of the Iowa Agriculture and Home Economics Experiment Station, Iowa State University, Project No. 3311. Mention of vendor or product names is for presentation clarity and does not imply endorsement by the authors or their affiliations, or exclusion of other suitable products.

This article is from Transactions of the ASAE 46, no. 2 (2003): 491–497.



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