Matheus Paula Reis

Accurately determining nutrient requirements based on animal performance and environmental conditions is essential to developing feeding strategies that optimize resource utilization, enhance productivity, and improve sustainability in poultry production. Traditional empirical dose–response approaches, while practical, are constrained by their experimental conditions. These static models are limited in their applications under variable conditions such as genetic strain, environmental factors, and age. This review aims to promote the use of dynamic factorial models for predicting energy and amino acid requirements in poultry. These models integrate key biological parameters, such as growth and tissue deposition, into nutrient utilization models for implementation in feeding programs. This review presents models for the principal poultry categories (broiler chickens, laying hens, and broiler breeders), based on biological assays developed over two decades of research at the Poultry Science Laboratory of the São Paulo State University (UNESP-Jaboticabal). The principle of the model is based on the growth potential described by the Gompertz function for protein growth, as well as allometric relationships between body protein and the other components (lipid, ash, and water) to predict tissue deposition rates. Body composition was estimated using in vivo measurements such as dual-energy X-ray absorptiometry and indirect calorimetry. Factorial models integrated dynamic growth (whole-body mass or protein growth) and product yield rates (body weight gain, egg mass, protein, and lipid deposition) as inputs to partition the energy and amino acids into maintenance, growth, and reproduction. Energy models were further adjusted for environmental temperature, while amino acid models account for the utilization efficiency determined for each amino acid. The models presented here are effective for estimating energy and amino acid requirements, which can help nutritionists define feeding programs adapted to each production condition, improving productivity and sustainability.

This study aimed to estimate the standardized ileal digestible leucine intake (SID-Leu_i, mg) in laying hens for maintenance, and to describe the response in laying hens to SID-Leu_i, thereby providing the information required to determine the optimum economic intake of SID-Leu for laying hens. Two nitrogen balance series, one balanced and the other unbalanced with respect to leucine (Leu), were used to estimate the SID-Leu requirement for maintenance using 36 roosters per series. The roosters were randomly distributed among the six levels of Leu with each level being replicated six times. The six diets were formulated to contain 0.0, 3.5, 6.9, 10.4, 13.9, or 17.4 g/kg of SID-Leu for the unbalanced series and 0.0, 4.0, 8.0, 12.0, 16.0, or 20.0 g/kg of SID-Leu for the balanced series. The SID-Leu_i maintenance requirement was calculated as 144 mg/bird d, 66 mg/kg d, 74 mg/kg^0.75d or 395 mg/BP_m^0.73d. For the response trial, 120 individually caged laying hens (63 weeks old) were randomly distributed among eight treatments with 15 replicates. To estimate the SID-Leu_i for the population of hens, the Reading Model was fitted to the data using body weight (BW, kg), SID-Leu_i and egg output (EO, g). The Reading Model calculated the mg SID-Leu_i = 11.6 EOmax + 43.4 BW. The efficiency of SID-Leu utilization for laying hens was estimated to be 79%.

The time-energy budget method estimates the energy used for physical activity (PA) based on recorded daily patterns and indirect calorimetry. Nevertheless, information about individual energy cost ...

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.