Feeding Effects on Broiler Thermobalance During Thermoneutral and High Ambient Temperature Exposure

Two experiments were conducted to estimate feed consumption effects on broiler thermobalance defined as heat production (H), evaporative heat loss (E), sensible heat loss (S), and change in body heat content (HC). Birds were housed at 24 C in the first study, 32 to 35 C in the second study, and forcefed in both studies to 0, 3, 6, and 9% of body weight kg.66 (MWT) each day. Starved bird H averaged 4.8 and 4.9 kcal/h per MWT within the thermoneutral (TN) and heat stress (HS) environments, respectively. Heat production increased linearly to 5.9 in TN and 6.2 kcal/h per MWT in HS as feeding level rose to 9% of MWT. Route of heat dissipation varied with environment. Within TN (Experiment 1), the increased heat load, with elevated feed consumption, was dissipated by increased (P < .01) S solely, as E remained constant (P > .1). Within HS (Experiment 2), E increased (P < .01) from 1.8 to 2.4 kcal/h per MWT. Viewed over experiments, S was 38% lower and E 67% higher during HS than TN. These data indicate that H increases with feeding level, that broilers preferentially dissipate heat as S when environmental conditions permit, and that feed consumption exacerbates bird HC rise when environmental conditions limit S.