High dietary zinc and glutamine do not improve the performance or reduce excreta moisture of broiler chickens fed diets with and without magnesium supplementation

Effects of Dietary Supplementation of Zinc Oxide Quantum Dots on Growth Performance and Gut Health in Broilers

This study aims to investigate the effect of different levels of zinc oxide quantum dots (ZnO-QDs) on the growth performance and gut health in broilers. A total of 1125 1-day-old Ross 308 broilers were randomly divided into five groups with 15 replicates of 15 chicks each. The broilers were fed basal diets supplemented with 0, 40, 80, 120, or 160 mg Zn/kg as ZnO-QDs for 6 weeks. The results showed that dietary 80 and 120 mg Zn/kg ZnO-QD supplementation increased (P < 0.05) average daily gain (1.4-1.7%) and reduced feed conversion ratio (1.3%) compared to the basal diet group during various experimental periods. Meanwhile, 80 mg Zn/kg ZnO-QD supplementation increased (P < 0.05) trypsin activity (25.4%), villus height, and the ratio of villus height to crypt depth in the jejunum. Moreover, 80 mg Zn/kg ZnO-QD supplementation increased (P < 0.05) the activities of glutathione reductase (47.7%) and superoxide dismutase (30.9%), while 120 mg Zn/kg ZnO-QD supplementation decreased (P < 0.05) glutathione peroxidase activity (27.1%) in the jejunum. Furthermore, 40 mg Zn/kg ZnO-QD supplementation down-regulated (P < 0.05) the expression of genes; interleukin-2, transforming growth factor β (TGF-β), Cathelicidin-1, Cathelicidin-2, Cathelicidin-3, and Occludin, while 80-160 mg Zn/kg ZnO-QD supplementation up-regulated (P < 0.05) Claudin-2 expression in the jejunum. In conclusion, dietary ZnO-QD supplementation improved growth performance of broilers potentially by enhancing their intestinal health status. Based on nonlinear regression analysis, the appropriate level of ZnO-QD supplementation would be from 98.2 to 102.5 mg Zn/kg.

The potential of glutamine supplementation in reduced-crude protein diets for chicken-meat production

This review explores the potential of including glutamine, a so-called non-essential amino acid, in the formulation of reduced-crude protein (CP) diets for broiler chickens. There is a precedent for benefits when including glycine and serine in reduced-CP diets. Fundamentally this is due to decreases in non-essential amino acid concentrations in reduced-CP diets - an unavoidable consequence of reducing CP without amino acid supplementation. The situation for glutamine is complicated because analysed dietary concentrations are very rarely provided as standard assays do not differentiate between glutamine and glutamate and are reported on a combined basis as glutamic acid. The dietary requirement for glutamic acid is approximately 36.3 g/kg but it is increasingly unlikely that this requirement will be met as dietary CP levels are progressively reduced. Glutamine is an abundant and versatile amino acid and constitutes 50.5 mg/g of whole-body chicken protein and is the dominant free amino acid in systemic plasma where it has been shown to provide 22.6% (139.9 of 620.3 μg/mL) of the total in birds offered 215 g/kg CP, wheat-based diets. In addition to dietary intakes, glutamine biosynthesis is derived mainly from the condensation of glutamate and ammonia (NH3) catalysed by glutamine synthetase, a reaction that is pivotal to NH3 detoxification. Glutamate and NH3 are converted to glutamine by phosphate-dependent glutaminase in the reciprocal reaction; thus, glutamine and glutamate are interchangeable amino acids. However, the rate of glutamine biosynthesis may not be adequate in rapidly growing broiler chickens and exogenous and endogenous glutamine levels are probably insufficient in birds offered reduced-CP diets. The many functional roles of glutamine, including NH3 detoxification and maintenance of acid-base homeostasis, then become relevant. Twenty feeding studies were identified where dietary glutamine supplementation, usually 10 g/kg, was evaluated in birds kept under thermoneutral conditions. On balance, the outcomes were positive, but the average dietary CP was 213 g/kg across the twenty feeding studies, which indicates that CP and, in turn, glutamine concentrations would have been adequate. This suggests that glutamine inclusions in reduced-CP diets hold potential and consideration is given to how this may be best confirmed.

Current experimental models, assessment and dietary modulations of intestinal permeability in broiler chickens

Maintaining and optimising the intestinal barrier (IB) function in poultry has important implications for the health and performance of the birds. As a key aspect of the IB, intestinal permeability (IP) is mainly controlled by complex junctional proteins called tight junction proteins (TJ) that link enterocytes together. The disruption of TJ is associated with increased gut leakage with possible subsequent implications for bacterial translocation, intestinal inflammation, compromised health and performance of the birds. Despite considerable data being available for other species, research on IP in broiler chickens and in general avian species is still an understudied topic. This paper reviews the available literature with a specific focus on IP in broiler chickens with consideration given to practical factors affecting the IP, current assessment methods, markers and nutritional modulation of IP. Several experimental models to induce gut leakage are discussed including pathogens, rye-based diets, feed deprivation and stress-inducing agents such as exogenous glucocorticoids and heat stress. Although various markers including fluorescein isothiocyanate dextran, expression of TJ and bacterial translocation have been widely utilized to study IP, recent studies have identified a number of excreta biomarkers to evaluate intestinal integrity, in particular non-invasive IP. Although the research on various nutrients and feed additives to potentially modulate IP is still at an early stage, the most promising outcomes are anticipated for probiotics, prebiotics, amino acids and those feed ingredients, nutrients and additives with anti-inflammatory properties. Considerable research gaps are identified for the mechanistic mode of action of various nutrients to influence IP under different experimental models. The modulation of IP through various strategies (i.e. nutritional manipulation of diet) may be regarded as a new frontier for disease prevention and improving the health and performance of poultry particularly in an antibiotic-free production system.

Intestinal Barrier Function and Performance of Broiler Chickens Fed Additional Arginine, Combination of Arginine and Glutamine or an Amino Acid-Based Solution

Two experiments were conducted to investigate the effect of arginine (Arg); the combination of Arg and glutamine (Gln); as well as an amino acid-based solution (MIX) containing Arg, Gln, threonine (Thr), and grape extract, on performance, intestinal permeability, and expression of selected mechanistic genes. Using 240 male Ross 308 off-sex broiler chickens, four experimental treatments were replicated six times with 10 birds per replicate. The experimental treatments included 5 g/kg Arg, 2.5 g/kg Arg and 2.5 g/kg Gln, and 1 g/kg MIX added to a basal diet as control. In the second study, the four dietary treatments were then given to 24 birds with or without a synthetic glucocorticoid, dexamethasone (DEX), as a gut dysfunction model. Feed conversion ratio was improved by all the supplemented treatments from day 7 to 35 of age (p < 0.001). DEX injections increased (p < 0.001) the intestinal permeability in all treatments, which tended to be reversed by Arg or MIX. Additional Arg, Arg-Gln, and MIX suppressed (p < 0.05) the overexpression of IL-1β generated by DEX. Feeding birds with MIX treatment increased (p < 0.05) expression of SGLT-1 and glutathione synthetase. In conclusion, tested amino acid supplements were effective in improving feed efficiency and restraining intestinal inflammation caused by DEX through IL-1β pathway.

Glutamine improves heat stress-induced oxidative damage in the broiler thigh muscle by activating the nuclear factor erythroid 2-related 2/Kelch-like ECH-associated protein 1 signaling pathway

The aim of the present study was to evaluate the effect of glutamine (Gln) on modulating heat stress–induced oxidative damage in the broiler thigh muscle through nuclear factor erythroid 2–related 2/Kelch-like ECH-associated protein 1 (Nrf2-Keap1) pathway. Three-hundred 22-day-old Arbor Acres broilers were reallocated into 5 groups: a control group (24 °C) fed with basal diet and 4 heat stress (HS) groups (34 °C for 8 h/D) fed with basal diet containing 0, 0.5, 1.0, and 1.5% Gln. This experiment lasted 21 D. Heat stress decreased (P < 0.05) pH, redness, and Gln levels, and increased (P < 0.05) luminance, water loss rate, and cooking loss (CL) values of the thigh meat. Compared with the HS group, supplementation with 1.5% Gln increased (P < 0.05) pH, redness, and Gln levels, but decreased (P < 0.05) luminance and CL values in the thigh meat. There were significant decreases (P < 0.05) in glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), total antioxidant capacity (T-AOC), and Nrf2 levels, but significant increases (P < 0.05) in the malondialdehyde (MDA) and Keap1 levels of the thigh muscle after HS treatment. Compared with the HS group, supplementation with 1.0, and 1.5% Gln decreased (P < 0.05) MDA and Keap1 levels; supplementation with 1.5% Gln increased (P < 0.05) GSH, GSH-Px, T-AOC, CAT, SOD, and Nrf2 levels in the thigh muscle of heat-stressed broilers. Furthermore, HS decreased (P < 0.05) Nrf2, SOD, CAT, and GSH-Px mRNA expression levels, but increased (P < 0.05) Keap1 mRNA level in the thigh muscle of broiler. Dietary supplementation with 1.5% Gln increased (P < 0.05) Nrf2, GSH-Px, CAT, and SOD mRNA expression levels, but decreased (P < 0.05) Keap1 mRNA level in the thigh muscle of heat-stressed broilers. In conclusion, dietary Gln improved the resistance of heat-stressed broiler muscles to oxidative damage possibly through reversing the muscle Gln level and inducing the expression of the Nrf2-Keap1 pathway.

Performance, intestinal permeability, and gene expression of selected tight junction proteins in broiler chickens fed reduced protein diets supplemented with arginine, glutamine, and glycine subjected to a leaky gut model

Changing dietary protein and amino acids may impact intestinal barrier function. Experiments were conducted in broiler chickens to evaluate supplementation of L-glutamine, glycine, and L-arginine in a reduced protein (RP) diet. Experiment 1 examined the growth performance of broilers fed 5 dietary treatments: 1) a standard diet; 2) an RP diet (193.9 g/kg CP in grower and 176.9 g/kg CP in finisher); 3) RP diet supplemented with 10 g/kg L-Gln; 4) RP diet supplemented with 10 g/kg Gly; 5) RP diet supplemented with 5 g/kg L-Arg. Each experimental diet was replicated 6 times with 10 birds per replicate. In a subset of 96 birds, experiment 2 tested the 4 RP diets with and without dexamethasone (DEX) to induce leaky gut. Each diet was replicated 24 times. Fluorescein isothiocyanate dextran (FITC-d) was used to test intestinal permeability (IP). Gene expression of selected tight junction proteins in ileal and jejunal tissues was assayed by quantitative PCR. From day 7 to 35, the RP diet increased feed intake (FI) (P < 0.05) and body weight gain (BWG) compared with the standard diet while Gln reduced FI and BWG (P < 0.05) compared with RP. Gly had no effect on BWG or FCR. Supplementation of Arg improved FCR from day 21 to 35 and day 7 to 35. In experiment 2, Arg tended to lower FITC-d (P = 0.086). DEX increased passage of FITC-d into the serum (P < 0.001). The villi surface area was increased in birds fed higher Arg (P < 0.05). DEX and diet interacted (P < 0.01) for jejunal claudin-3 mRNA level where DEX upregulated claudin-3 for all diets except the Arg diet. In summary, with a moderate reduction of protein, satisfactory performance can be obtained. Although Gln and Gly had no demonstrable positive effect on IP and performance of broilers, increasing the dietary Arg by approximately 140% improved FCR and showed indications of improved intestinal barrier function of birds fed an RP diet under a stress model.