Nicarbazin effects on broiler thermobalance during high ambient temperature stress.

Two experiments were conducted to measure the effects of nicarbazin (125 ppm) on heat production (H), evaporative heat loss (E), sensible heat loss (S), and heat content change (HC) of broilers during heat stress. Feed consumption effects on thermobalance were equalized in both studies by force feeding at 7% of metabolic body weight (MWT; body weight.66) daily. In Experiment 1, using broilers not acclimated to heat stress, nicarbazin increased H (P < .05) (9.5 vs. 9.0 kcal/h per MWT) and body temperature (P = .08), reduced (P < .05) respiration rate, and had no impact on E or S (P > .1). In contrast, the bird acclimated to heat stress used in Experiment 2 exhibited similar (P > .1) thermobalance responses irrespective of nicarbazin supplementation. The data suggests that heat-stress-mediated nicarbazin toxicity may be related to H and further that nicarbazin's heat-stress-mediated toxicity is reduced in HS-acclimated chicks.