Research Note: Broiler Acclimation to Heat Distress and Feed Intake Effects on Body Temperature in Birds Exposed to Thermoneutral and High Ambient Temperatures

Relationships between ambient temperature, bird acclimation to cycling temperature, heat distress, and feed consumption were evaluated in two experiments. In the first experiment, birds previously acclimated to cycling temperature heat distress (24 to 35 C) for two 24-h cycles were observed to have 24% lower (P < .01) feed consumption than birds previously housed at 24 C and experiencing their first heat distress exposure. A significant (P < .01) acclimation history by ambient temperature interaction was detected, with acclimated birds having a higher rectal temperature (42.3 versus 41.2 C) when housed at 24 C and a lower rectal temperature (44.2 versus 44.6 C) when exposed to 35 C than did the unacclimated controls. In the second experiment, feed intake and acclimation effects were separated by precision-feeding birds 0, 5, and 10% of body weight. Rectal temperature in the 24 C and 35 C environments increased linearly (P < .01) as feeding level increased for both acclimated and unacclimated birds. Similar to the first experiment, an ambient temperature by acclimation history interaction was detected (P < .01), with acclimated birds exhibiting increased body temperature when housed in thermoneutral environments and lower body temperature when exposed to high ambient temperature distress. Data also indicate that feed intake plays a significant role in the acclimation process; that bird acclimation to heat distress has metabolic effects independent of feed consumption; and that either 1) the heat-distressed, acclimated bird has the capacity to shift exothermic processes from the heat-distressed to cooler time periods; 2) that heat dissipation mechanisms require greater than 12 h to restore normal body temperature; or 3) the birds' set point is elevated when exposed to cycling high ambient temperature distress.