Air velocity (AV) is one of the main environmental factors involved in thermoregulation,
especially at high ambient temperatures. To elucidate the effect of AV on performance
and thermoregulation of 4- to 7-wk-old broiler chickens, an experiment was conducted
using 4 different AV (0.8, 1.5, 2.0, and 3.0 m/s) at constant ambient temperatature
(35 +/- 1.0 degrees C) and RH (60 +/- 2.5%). BW, feed intake, and fecal and urinary
excretions were monitored in individuals and were used to calculate the amount of
energy expended for maintenance. Infrared thermal imaging radiometry was used to measure
surface temperatures for the calculation of heat loss by radiation and convection.
Brachial vein blood was collected for plasma osmolality and arginine vasotocin analysis.
Broilers performed optimally at an AV of 2.0 m/s. Energy expenditure for maintenance
was significantly higher under these conditions, suggesting the ability to direct
a sufficient amount of energy to control body temperature, while maintaining relatively
high growth rates. Convective heat loss increased significantly with increasing AV,
whereas radiative heat loss was not affected. Sensible heat loss, expressed as a percentage
of energy expenditure for maintenance, was significantly higher at 2.0 m/s compared
with 0.8 m/s but significantly lower than that of 3.0 m/s. The high level of heat
loss observed at 3.0 m/s probably affected body water balance, as supported by significantly
higher plasma osmolality, arginine vasotocin concentration, and the hyperthermic status
of these birds. It can be concluded that AV of 2.0 m/s enables broilers to maintain
proper performance together with efficient thermoregulation and water balance under
harsh environmental conditions.