Rony Riveros Lizana

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.

Two trials evaluated the effects of dietary protease inclusion in weaned piglets fed diets with or without crude protein (CP) reduction, focusing on performance, intestinal health, and amino acid digestibility. In Trial I, 270 piglets (21–63 days) received six treatments: control (PC), PC with 100 g/ton protease A (PC+A), CP reduced by 1.0% (NC1) or 1.5% (NC1.5), NC1.5 with 50 g/ton protease A (NC1.5+A), and NC1.5 with 50 g/ton protease B (NC1.5+B). PC+A improved weight gain, feed intake, and feed conversion compared with NC1.5+A. The incidence of diarrhea was reduced in animals fed protease-supplemented diets (PC+A, NC1.5+A and NC1.5+B). PC had greater ileal villus height than NC1.5+B, and PC+A showed a higher jejunal villus-to-crypt ratio than reduced CP groups. NC1.5+B increased jejunal expression of IL-6, TNF-α, and haptoglobin. In Trial II, 12 ileal-cannulated piglets received diets with or without protease A. Protease improved the standardized ileal digestibility (SID) of methionine+cysteine and tryptophan but reduced the SID of glycine and proline. While protease supplementation can improve some amino acids (Met+Cys and Thr) protein digestibility, our findings suggest it cannot fully replace careful amino acid balancing in CP-reduced diets. However, protease-supplemented diets were associated with improved intestinal morphometry and a reduced incidence of diarrhea.

This study aimed to determine the optimal methionine:cystine (Met:Cys) ratio in diets with reduced crude protein (CP). Two trials were carried throughout14 to 28 days. In trial 1, 1200 broiler chicks were distributed under a random design of ten treatments in a 2 × 5 factors of variability arrangement with two protein levels (21.5 and 19.5 % CP) and five digestible Met:Cys ratios (42:58, 46:54, 50:50, 54:46, and 58:42). Each treatment consisted of six replicates each, with 20 birds per experimental unit. In trial 2, 36 birds were selected and randomly allocated in six treatments with three replications each to carry out a nitrogen (N) balance study. The treatments were designed in a 2 × 3 factorial arrangement with two levels of protein (21.5 and 19.5 % CP) and three Met:Cys ratios (42:58, 50:50, and 58:42). Statistical analyses were performed as two-way analysis of variance (ANOVA) with interactions and main effects compared by Tukey's test. All statistical procedures were performed using the PROC GLM, and PROC NLIN was used to fit the quadratic broken line. No interaction was observed for weight gain, but there was a significant effect of the Met:Cys p < 0.05. There was a significant interaction between Met:Cys and CP level for feed intake (FI) and feed conversion rate p < 0.05. The CP level did not affect N retention (NR) p > 0.05 but significantly affected N intake (N_in), excretion (N_exc), and utilization (k_N) efficiency. Therefore, an average Met:Cys ratio of 52:48 promoted a better performance response, improved in k_N, and even CP reduction.

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.

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.