Data experiment 2023

The current study was conducted during March/April (the hot, dry season) in Thailand. It was hypothesized that the conversion from feed to bodyweight (<b>BW</b>) gain is more efficient in isocaloric-fed broilers housed under thermoneutral (<b>TN</b>) conditions instead of heat stress (<b>HS</b>). Given the lack of data, it was also of interest to measure the expression of avian uncoupling proteins (<b>avUCP</b>) in brain tissue of broilers. A total of 180 Ross 308 day-old broilers were randomly allocated to three treatments: ad libitum feeding under TN conditions (<b>Ad</b>-<b>Lib</b> <b>TN</b>), ad libitum feeding under HS conditions (<b>Ad</b>-<b>Lib</b> <b>HS</b>), and pair-fed under TN conditions (<b>PF</b> <b>TN</b>) with feed intake matched to HS broilers.Broilers exposed to HS showed increased open-beak breathing, altered posture, and higher respiratory frequency (96% had 151-250 bpm) indicating increased heat dissipation. Water intake rose, while partial CO2 pressure (<b><i>P</i></b><b>CO2</b>) was ~25% lower in HS broilers. The HS broilers also had a 5% higher cloacal temperature confirming HS conditions. Bodyweight, daily gain and feed intake were negatively affected by HS in ad libitum-fed birds and FCR worsened under HS. However, the FCR was found to be similar between Ad-Lib HS and PF TN thereby disproving our hypothesis. The expression of avUCP in the <i>m. pectoralis</i>, but not in the brain, was increased under HS. It thus appears that the expression of avUCP in brain tissue is not sensitive to HS. The results indicate that energy for heat dissipation behavior is quantitatively unimportant in determining the FCR in HS broilers.