Objective: This study aimed to evaluate the effect of the ad libitum and restricted feeding regimen on fasting heat production (FHP) and body composition.Methods: Twelve Hubbard broilers breeders were selected with the same body weight and submitted in two feeding regimes: Restricted (T1) with feed intake of 150 g/bird/d and ad libitum (T2). The birds were randomly distributed on the treatments in two runs with three replications per treatment (per run). The birds were adapted to the feed regimens for ten days. After that, they were allocated in the open-circuit chambers and kept for three days for adaptation. On the last day, oxygen consumption (VO2) and carbon dioxide production (VCO2) were measured by 30 h under fasting. The respiratory quotient (RQ) was calculated as the VCO2/VO2 ratio, and the heat production (HP) was obtained using the Brower equation (1985). The FHP was estimated throughout the plateau of HP 12 hours after the feed deprivation. The body composition was analyzed by dual-energy X-ray absorptiometry scanning at the end of each period. Data were analyzed for one-way analysis of variance using the Minitab software.Results: The daily feed intake was 30 g higher to T2 (p<0.01) than the T1. Also, the birds of the T2 had significatively (p<0.05) more oxygen consumption (+3.1 L/kg0.75/d) and CO2 production (+2.2 L/kg0.75/d). That resulted in a higher FHP 359±14 kJ/kg0.75/d for T2 than T1 296±17.23 kJ/kg0.75/d. In contrast, the RQ was not different between treatments, with an average of 0.77 for the fasting condition. In addition, protein and fat composition were not affected by the treatment, while a tendency (p<0.1) was shown to higher bone mineral content on the T1.Conclusion: The birds under ad libitum feeding had a higher maintenance energy requirement but their body composition was not affected compared to restricted feeding.

This study aimed to evaluate energy utilization and propose models for metabolizable and net energy requirements in broiler breeders during the egg production phase. Sixty Cobb500 broiler breeders aged between 29 and 65 wk were randomly assigned to 3 feeding levels. At each age, 6 birds were adapted for 8 d to 3 levels of metabolizable energy intake (MEi), established based on the amount of feed allocated: 1) the amount of feed recommended in the guideline, 2) 25% above, and 3) 25% below. The birds were housed in respirometry chambers for 6 d (1 adaptation, 4 feeding state, 1 fasting) to measure oxygen consumption and carbon dioxide production to calculate heat production (HP) and fasting HP (FHP). Daily measurements of feed intake, egg weight, egg production, and total excreta were recorded. Variables of MEi, HP, and retained energy (RE) in the egg were calculated, while RE in the body and its partitioning into fat and protein in the egg and body were calculated from MEi, total HP (THP), and RE in the egg. Statistical analysis involved linear regression of multiple factors with MEi and age (categorical) as the independent variables. Pearson correlation analysis was conducted to investigate the relationship between visceral mass and the evaluated variables. The study proposed mixed models for developing models of energy requirements for both metabolizable (ME) and net systems (NE). The study found that FHP (average 259 ± 20.08 kJ/kg^0.75*d) remained constant throughout the production cycle regardless of the MEi level (P > 0.05). The efficiency of energy utilization for depositing protein and fat in the body changed with the bird's age. The lower error model was considered to select ME requirements for maintenance, egg, and gain efficiencies, disregarding the effect of age. The efficiencies were 0.89, 0.78, and 0.80 for maintenance, gain, and egg production, respectively. The NE was unaffected by age and showed a lower error than the ME model. The NE system was found to be more accurate in expressing the energy requirements of broiler breeders.

Objective: The objective of this study was to describe a methodological procedure to quantify the heat production (HP) partitioning in basal metabolism or fasting heat production (FHP), heat production due to physical activity (HPA), and the thermic effect of feeding (TEF) in roosters.Methods: Eighteen 54-wk-old Hy Line Brown roosters (2.916±0.15 kg) were allocated in an open-circuit chamber of respirometry for O2 consumption (VO2), CO2 production (VCO2), and physical activity (PA) measurements, under environmental comfort conditions, following the protocol: adaptation (3 d), ad libitum feeding (1 d), and fasting conditions (1 d). The Brouwer equation was used to calculate the HP from VO2 and VCO2. The plateau-FHP (parameter L) was estimated through the broken line model: HP = U×(R–t)×I+L; I = 1 if tR; Where the broken-point (R) was assigned as the time (t) that defined the difference between a short and long fasting period, I is conditional, and U is the decreasing rate after the feed was withdrawn. The HP components description was characterized by three events: ad libitum feeding and short and long fasting periods. Linear regression was adjusted between physical activity (PA) and HP to determine the HPA and to estimate the standardized FHP (st-FHP) as the intercept of PA = 0.Results: The time when plateau-FHP was reached at 11.7 h after withdrawal feed, with a mean value of 386 kJ/kg0.75/d, differing in 32 kJ from st-FHP (354 kJ/kg0.75/d). The slope of HP per unit of PA was 4.52 kJ/mV. The total HP in roosters partitioned into the st-FHP, termal effect of feeding (TEF), and HPA was 56.6%, 25.7%, and 17.7%, respectively.Conclusion: The FHP represents the largest fraction of energy expenditure in roosters, followed by the TEF. Furthermore, the PA increased the variation of HP measurements.

Indirect calorimetry (IC) is a widely used method to study animal energy metabolism by measuring gas exchange. The accuracy of IC depends on detecting variations in signals reflecting the metabolic response, which can be challenging due to measurement noise and external factors. This study proposes a methodology to validate IC systems, including an easy-to-use spreadsheet for data computing, to verify accuracy and detect whole-system leaks. We conducted a recovery test using a simulation of CO₂ dynamics in MS Excel and injecting a known CO₂ concentration into four respirometry chambers. The thought flow rate of CO₂ was observed and compared to the expected rate from the simulation. Data filtering and computing, including a detailed calculation of signals calibration, Bartholomew transformation, and noise reduction, was developed to obtain the gas exchange and heat production parameters using an open-circuit IC system. The results from the recovery test in our system show that the proposed methodology is accurate and precise. The proposed methodology and recovery test can be used to standardize the validation of IC systems together with adequate data computing, providing accurate measurements of animal energy metabolism in different environmental conditions and energy utilization from feeds.

The use of antibiotics in poultry farming has been associated with bacterial resistance in humans, leading to a ban on their inclusion in chicken diets. Therefore, the objective was to evaluate the effects of probiotics and β-mannanase on the growth performance and intestinal health of broiler chickens challenged by Eimeria maxima and Clostridium perfringens. For this, 2100 one-day-old male Ross 308 chicks were used. The treatments were as follows: T1—Negative control (NC) unchallenged birds; T2—Positive control (PC) challenged with E. maxima + C. perfringens; T3—PC + Antibiotic (Enramycin 8%-125 g/ton); T4—PC + β-mannanase (Hemicell^HT; 300 g/ton); T5—PC + probiotic (Protexin^TM; 150 g/ton); T6—PC + β-mannanase + probiotic. Significant differences (p < 0.05) were observed from 1 to 42 days in the variables body weight, body weight gain and feed intake, and the NC treatment presented higher values compared to the PC and PC + probiotic groups. The villus/crypt ratio in the duodenum increased in the PC + β-man + prob treatment, differing from the NC, PC and PC + probiotic (p < 0.05) treatments. The use of β-mannanase, probiotics or both together is effective to mitigate the effects of production challenges, through the maintenance of the intestine by modulating action on the cecum microbiome and intestinal morphometry.