Understanding the mechanism of energy expenditure under a health challenge in birds to supply the energy and attenuate the effects of the sanitary problems is essential. This study aimed to evaluate the daily energy expenditure in growing broiler chicks under health challenges. Forty-eight day-old male Ross 308 broiler chicks 13- day-old were allocated into open-circuit chambers. The birds were randomly distributed in two treatments (Challenge with E. maxima and C. perfringens – C and no challenge pairfeeding group – PF), with three replicates of eight birds, each with the same body weight. On the 14-old-day, the birds of the challenged treatment were inoculated with 1ml of Eimeria maxima (7×103 oocysts/ml) by oral gavage. On days 18, 19, and 20 was inoculated 2.5×106 CFU of Clostridium perfringens. The PF group was inoculated with 1 ml of saline solution. The gas exchange was measured daily during the feeding condition from 14 to 22-old-day. Also, was measured body weight (BW) and the feed intake (FI) to calculate the feed efficiency (FE). The heat production (HP) was obtained from the oxygen consumption (VO2) and carbon dioxide production (VCO2), using the Brouwer (1965) equation, and the respiratory quotient was obtained from VCO2/VO2 ratio. The data was analyzed by ANOVA two-way considering each day as a longitudinal factor, using Minitab v.20 statistical software. The FI was similar between treatments, for the FE was shown an interaction between treatment and age (P<0.01). The difference (P<0.01) was shown on the first day before the E. maxima were inoculated (14, 15, and 16). The PF report hight values than C treatment (P<0.01) during all observation periods. The birds of the C group had a lower BW compared to PF (P<0.001). Challenge birds had a significantly higher HP (P=0.013) than PF treatment, with a difference of 32.1 KJ/kg0.75/d, but no interaction was observed. Also, the RQ was not different between treatments (P=0.593), but it was affected by the longitudinal factor (P<0.001) and was shown interaction (p=0.034). During the challenge period (between 18-21 d), RQ was higher than 1 in challenged birds.
In conclusion, a moderate health challenge affects feed efficiency utilization and increases energy expenditure, representing energy loss.