Effect of dietary tryptophan supplementation on growth performance, immune response and anti-oxidant status of broiler chickens from 7 to 21 days

Untargeted metabolomics analysis of the spleens of ducks infected with Clostridium perfringens type A

BACKGROUND

The aim of this study was to investigate the metabolomic changes in the spleens of ducks artificially infected with Clostridium perfringens type A. Twenty-four healthy ducks aged 1 d were used for this purpose. After acclimatization for 37 d, the ducks were divided into 4 treatment groups (n = 6): the control group (normal group), infection Group 1 (66 h), infection Group 2 (90 h) and infection Group 3 (114 h). The ducks in the corresponding infection group were challenged with 8 mL of C. perfringens type A bacterial solution (1 × 108 CFU/mL) for 4 days. The experimental ducks were culled at 0 h, 66 h, 90 h and 114 h after infection, and the ducks were sacrificed for spleen sampling at the end of the experiment. Autopsy observations, spleen pathological changes and pathogen nucleic acid detection were also performed. Finally, the changes in the metabolic profile of the spleen were investigated via a metabolomics approach.

RESULTS

At necropsy, the pathological changes in C. perfringens type A infection included enlarged, haemorrhagic and mottled spleens. Histopathology examination revealed that the ducks in the infection group had damaged spleen tissue structures, dilated spleen sinuses with congestion and bleeding, an extreme decrease in lymphocytes, and massive inflammatory cell infiltration in the splenic tissue. Spleen lesions were observed and PCR tests were positive in ducks in the infection group, indicating that a model of C. perfringens type A infection was successfully established in this study. Compared with those in the normal group, 14, 15 and 20 differentially abundant metabolites were identified after 66, 90 and 114 h, respectively, of C. perfringens type A infection of duck spleens, mainly including indolin-2-one, 3-methylindole, 4-hydroxy-2-quinolinecarboxylic acid, indole-3-methyl acetate, uric acid, 2'-deoxyinosine, urate, xanthine, 3-succinoylpyridine, nicotinic acid, phenylacetylglycine, histamine and phosphoenolpyruvate. Pathway analysis revealed that these metabolites were mainly involved in tryptophan metabolism, purine metabolism, nicotinate and nicotinamide metabolism, phenylalanine metabolism, histidine metabolism, phenylalanine, tyrosine and tryptophan biosynthesis, tyrosine metabolism, arginine and proline metabolism, arachidonic acid metabolism, and caffeine metabolism.

CONCLUSIONS

These findings suggest that C. perfringens type A infection causes a duck spleen inflammatory response and immune response in infected ducks through indolin-2-one, 3-methylindole, 4-hydroxy-2-quinolinecarboxylic acid and tryptophan metabolism, purine metabolism, nicotinic acid and nicotinamide metabolism, which provides a basis for understanding the pathogenesis of C. perfringens type A in ducks.

Gut-X Axis and Its Role in Poultry Bone Health: A Review

The normal development and growth of bones are critical for poultry health. With the rapid increase in poultry growth rates achieved over the last few decades, juvenile meat-type poultry exhibit a high incidence of leg weakness and lameness. These issues are significant contributors to poor animal welfare and substantial economic losses. Understanding the potential etiology of bone problems in poultry will aid in developing treatments for bone diseases. The gut microbiota represents the largest micro-ecosystem in animals and is closely related to many metabolic disorders, including bone disease. It achieves this by secreting secondary metabolites and coordinating with various tissues and organs through the circulatory system, which leads to the concept of the gut-X axis. Given its importance, modulating gut microbiota to influence the gut-X axis presents new opportunities for understanding and developing innovative therapeutic approaches for poultry bone diseases. In light of the extensive literature on this topic, this review focuses on the effects of gut microbiota on bone density and strength in poultry, both directly and indirectly, through the regulation of the gut-X axis. Our aim is to provide scientific insights into the bone health problems faced by poultry.

Tryptophan and/or canthaxanthin in quail diets: effects on performance, carcass traits, hematology, blood chemistry and hepatic antioxidant capacity

To enhance the health and performance of poultry, novel approaches have to be created. Using appropriate nutritional interventions to enhance body physiology and thus enhance productivity is one of these approaches. The purpose of the present investigation intended to examine how growing quail physiology and growth is affected by supplementing diets with tryptophan (Trp) and/or canthaxanthin (CX). The sum of 200 unsexed, 1-week-age Japanese quails (Coturnix coturnix japonica), with a nearly similar body weight (BW) of 33.50 ± 1.20 g, were assigned, in random, to four experimental groups. Each group consisted of five replicates, with 10 birds per replicate. Chicks in group 1 (T1) served as the control and were fed a basal diet without any supplementation from week 1 to week 5. The second (T2) and third (T3) groups received feed supplemented with 0.01 % Trp and 0.005 % CX, respectively. The fourth group (T4) was given a diet containing a combination of 0.01 % Trp and 0.005 % CX. Results indicated that supplementation with Trp, CX, or their combination significantly (P < 0.05) enhanced live BW and body weight gain (BWG) at 5 weeks. No noticeable variations in carcass characteristics were found across all treatments over the whole trial duration. Blood levels of high-density lipoprotein were considerably greater in the Trp and/or CX-fed group than in the control group. Adding Trp and/orCX to quail diets significantly (P < 0.05) decreased the activity of liver enzymes (alanine transaminase, ALT; aspartate transaminase, AST; alkaline phosphatase, ALP), along with reduced low-density lipoprotein (LDL) levels. Birds received diets with Trp and/or CX had higher values of antioxidant indices in serum and liver (P < 0.05), accompanied by low values of malondialdehyde compared to control group. We concluded that adding quail diet with Trp and/orCX had positive consequences on the growth performance and some physiological indices.

Effects of Tryptophan Supplementation in Diets with Different Protein Levels on the Production Performance of Broilers

Tryptophan plays an important role in the pig industry but has the potential to improve performance in the poultry industry. The purpose of this study was to examine the effects of tryptophan supplementation in diets with different protein levels on the feed intake, average daily gain (ADG), and feed conversion ratio (F/G) of broilers. A total of 180 twenty-one-day-old broilers (half male and half female) were weighed and randomly allocated to twelve groups, with six male and six female groups. Each group consisted of 15 broilers. The broilers were fed low- (17.2%), medium- (19.2%), or high- (21.2%) protein diets with or without extra tryptophan (up to 0.25%) during the 28-day experiment. Food intake and body weight were measured weekly during the trial period. Male broilers fed a medium-protein diet containing more tryptophan showed a lower F/G. In the low-protein diet groups, additional tryptophan caused a significant reduction in the feed intake of female broilers during the first two weeks. Moreover, the serum GLP-1, cholesterol, and bile acid levels, as well as the expression of FXR mRNA in the ileum, were significantly increased. Additionally, the FXR mRNA in the hypothalamus and the GCG and GLP-1R mRNAs in the ileum tended to increase in these broilers. In summary, the tryptophan concentration in the diet can influence the feed intake and metabolism of broilers. Under a standard diet, an appropriate amount of tryptophan is beneficial to the F/G of male broilers, while under a low-protein diet, tryptophan supplementation may cause a short-term reduction in the feed intake of female broilers by increasing serum GLP-1 and bile acid signals.

Impact of dietary digestible aromatic amino acid levels and stachyose on growth, nutrient utilization, and cecal odorous compounds in broiler chickens

This study evaluated the impact of dietary digestible aromatic amino acid (DAAA) levels and stachyose on growth, nutrient utilization and cecal odorous compounds in broiler chickens. A 3×2 two-factor factorial design: Three dietary DAAA levels (1.40, 1.54, 1.68%) supplemented with either 5 g/kg of stachyose or without any stachyose were used to create 6 experimental diets. Each diet was fed to 6 replicates of 10 birds from d 22 to 42. Findings revealed that broilers receiving a diet with 1.54% DAAA levels supplemented with 5 g/kg stachyose exhibited a significant boost in average daily gain and improved utilization of crude protein, ether extract, tryptophan, and methionine compared to other diet treatments (P < 0.05). As the dietary DAAA levels increased, there was a significant rise in the concentrations of indole, skatole, p-methylphenol, and butyric acid in the cecum of broilers (P < 0.05). The addition of stachyose to diets reduced concentrations of indole, skatole, phenol, p-methylphenol, acetic acid and propionic acid in the cecum (P < 0.05). The lowest concentrations of indole, phenol, p-methylphenol, volatile fatty acids and pH in cecum of broilers were observed in the treatment which diet DAAA level was 1.40% with stachyose (P < 0.05). In conclusion, dietary DAAA levels and stachyose had significant interactions on the growth, main nutrient utilization and cecal odorous compounds in broilers. The dietary DAAA level was 1.54% with 5 g/kg of stachyose can improve the growth performance, nutrient utilization. However, the dietary DAAA level was 1.40% with stachyose was more beneficial to decrease the cecal odor compound composition in broilers.

The Impact of Essential Amino Acids on the Gut Microbiota of Broiler Chickens

The research involving the beneficial aspects of amino acids being added to poultry feed pertaining to performance, growth, feed intake, and feed conversion ratio is extensive. Yet currently the effects of amino acids on the gut microbiota aren't fully understood nor have there been many studies executed in poultry to explain the relationship between amino acids and the gut microbiota. The overall outcome of health has been linked to bird gut health due to the functionality of gastrointestinal tract (GIT) for digestion/absorption of nutrients as well as immune response. These essential functions of the GI are greatly driven by the resident microbiota which produce metabolites such as butyrate, propionate, and acetate, providing the microbiota a suitable and thrive driven environment. Feed, age, the use of feed additives and pathogenic infections are the main factors that have an effect on the microbial community within the GIT. Changes in these factors may have potential effects on the gut microbiota in the chicken intestine which in turn may have an influence on health essentially affecting growth, feed intake, and feed conversion ratio. This review will highlight limited research studies that investigated the possible role of amino acids in the gut microbiota composition of poultry.

Protective impacts of mitochondria enhancers against thermal stress in poultry

Heat stress (HS) is still the essential environmental agent influencing the poultry industry. Research on HS in poultry has progressively acquired growing interest because of increased attention to climate alteration. Poultry can survive at certain zone of environmental temperatures, so it could be considered homoeothermic. In poultry, the normal body temperature is essential to enhance the internal environment for growth, which is achieved by normal environmental temperature. Recently, many studies have revealed that HS could cause mitochondrial dysfunction in broilers by inducing redox dysfunction, increasing uncoupling protein, boosting lipid and protein oxidation, and oxidative stress. Moreover, HS diminished the energy suppliers supported by mitochondria activity. A novel strategy for combating the negative influences of HS via boosting the mitochondria function through enrichment of the diets with mitochondria enhancers was also described in this review. Finally, the current review highlights the mitochondria dysfunction induced by HS in broilers and attempts to boost mitochondria functionality by enriching mitochondria enhancers to broiler diets.

Ceruloplasmin Interferes with the Assessment of Blood Lipid Hydroperoxide Content in Small Ruminants

Simple and inexpensive analytical methods for assessing redox balance in biological matrixes are widely used in animal and human diagnostics. Two of them, reactive oxygen metabolites (ROMs) and total oxidant status (TOS), evaluate the lipid hydroperoxide (LOOH) content of the sample and are based on iron-mediated mechanisms. However, these tests provide uncorrelated results. In this study, we compared these two tests in the blood serum of goat kids and lambs, together with an evaluation of ceruloplasmin (CP) oxidase activity. No significant correlation was found between ROMs and TOS, or between TOS and CP oxidase activity, in either species. Conversely, ROMs and CP oxidase activity were highly correlated in both kid and lamb samples (p < 0.001). A significant progressive reduction in the analytical signal in the ROMs assay was observed when sodium azide, an effective CP inhibitor, was added to the samples before the assay (p < 0.001). This decrease was related to sodium azide concentration (p < 0.01) and was not found when sodium azide was added at the same concentrations in the TOS assay. These findings suggest that ROMs, unlike TOS, may be affected by CP, which interferes with LOOH detection in blood samples.

Effects of protected complex of bio-factors and antioxidants on growth performance, serum biochemistry, meat quality, and intestinal antioxidant and immunomodulatory-related gene expressions of broiler chickens

One-day-old male broiler chickens (Ross 308) were assigned to 3 dietary treatments in a completely randomized design with 8 replicates per treatment, and 4 birds per replicate. The control group was fed a basal control diet, and the 2 test groups were fed the basal control diet supplemented with 150 and 300 mg/kg of protected complex of biofactors and antioxidants [P(BF+AOX)], respectively. The P(BF+AOx) is a combination of vitamins, L-tryptophan and biofactors such as fermentation extracts (Jefo Nutrition Inc., Saint-Hyacinthe, QC, Canada). Dietary P(BF+AOX) did not affect growth performance and breast meat quality (water holding capacity, cooking loss, shear force, and texture profile analysis), but the addition of 150 mg/kg of P(BF+AOX) decreased the relative weight of liver, heart, and spleen (P < 0.05). The addition of 150 mg/kg of P(BF+AOX) tended to increase (P = 0.051) the cold carcass yield. The addition of 150 and 300 mg/kg of P(BF+AOX) decreased (P = 0.002) the cooler carcass shrink, but the relative weight of fat pad increased (P = 0.032) in chickens fed 300 mg/kg P(BF+AOx) than in those of birds fed the control diet. On the other hand, the addition of 300 mg/kg of P(BF+AOX) decreased (P = 0.041) the serum level of uric acid compared with those of birds fed the basal diet. Broiler chickens fed diets supplemented with 150 mg/kg of diet had higher (P < 0.05) mRNA expressions of jejunal SOD1 and interleukins 6 and 10 (IL-6, IL-10). The findings suggest that P(BF+AOX) could be considered as a functional nutrient in broiler diets up to a concentration of 150 mg/kg because of its favorable effects on maintaining intestinal barrier function as well as carcass traits, while excess levels (300 mg/kg) had exhibited superior effect on the serum level of uric acid compared with those of birds fed the control diet.

Heat stress-induced intestinal barrier damage and dimethylglycine alleviates via improving the metabolism function of microbiota gut brain axis

Heat stress, a widely occurred in subtropical climate regions, causes ecosystem destruction, and intestine injury in humans and animals. As an important compound in the metabolic pathway of choline, dimethylglycine (DMG) shows anti-inflammatory effects. This study examines the beneficial effects of dietary DMG against heat stress-induced intestine injury and further explores the underlying molecular mechanisms using a broiler model. Here, we showed that DMG supplements exhibited positive effects to growth performance, as evidenced by the significantly increased body weight and feed conversion rate. These therapeutic effects attributed to repaired gut barrier integrity, increased content of anti-inflammatory cytokines IL-10, decreased content of pro-inflammatory cytokines IL-6, and down-regulated gene expression of the NF-κB signaling pathway. DMG treatment led to the reshaping of the gut microbiota composition, mainly increasing the short-chain fatty acid (SCFAs) strains such as Faecalibacterium, and Marvinbryantia. DMG treatment also increased two main members of SCFAs, including acetate acid and isobutyrate. Particularly, distinct effects were found which mediated the tryptophan metabolism in intestines such as increased tryptophan and 5-HT, which further alleviate the occurrence of intestinal barrier damage caused by heat stress. Additionally, DMG treatment promoted neuroendocrine function and stimulated the hypothalamic neurotransmitter metabolism by activating tryptophan metabolism in the hypothalamus. Overall, DMG supplementation effectively reduced the occurrence of intestinal inflammation induced by heat stress through modulating cecal microbial communities and improving the metabolism function of microbiota gut brain axis. Our findings revealed a novel mechanism by which gut microbiota could improve host health.

Tryptophan oxidation in young children with environmental enteric dysfunction classified by the lactulose rhamnose ratio

BACKGROUND

In young children, associations between linear growth faltering, environmental enteric dysfunction (EED), and the plasma kynurenine (Kyn)/tryptophan (Trp) ratio (KTR) have led to the proposal that higher Trp catabolism in response to intestinal/systemic inflammation limits Trp availability for protein synthesis, resulting in impaired growth.

OBJECTIVES

We sought to estimate the Trp oxidation rate and the Trp conversion rate to Kyn in young children with and without EED.

METHODS

Children aged 18-24 mo, from urban slums, were assigned to EED (n = 19) or no-EED (n = 26) groups on the basis of a urinary lactulose/rhamnose ratio (LRR) cutoff based on mean + 2 SDs of LRR (≥0.068) in normal age- and sex-matched, high-socioeconomic status children. Plasma KTR and fecal biomarkers of EED were measured. Trp oxidation in the fed state was measured using 13C1-Trp in an oral plateau feeding protocol.

RESULTS

The median (quartile 1, quartile 3) fasted KTR was 0.089 (0.066, 0.110) in children with EED compared with 0.070 (0.050, 0.093) in children with no EED (P = 0.077). However, there was no difference in fed-state Trp oxidation [median (quartile 1, quartile 3) 3.1 (1.3, 5.8) compared with 3.9 (1.8, 6.0) µmol/kg FFM/h, respectively, P = 0.617] or Trp availability for protein synthesis [42.6 (36.5, 45.7) compared with 42.5 (37.9, 46.9) µmol/kg FFM/h, respectively, P = 0.868] between the groups. In contrast, the median (quartile 1, quartile 3) fractional synthesis rates of Kyn [12.5 (5.4, 20.0) compared with 21.3 (16.1, 24.7) %pool/h, P = 0.005] and the fraction of Ala derived from Trp [0.007 (0.005, 0.015) compared with 0.012 (0.008, 0.018), P = 0.037], respectively, in the plasma compartment were significantly slower in the EED group. Fecal biomarkers of EED did not differ between the groups.

CONCLUSIONS

The static plasma KTR value is not a good indicator of the dynamic Trp flux down its oxidative pathway. In a poor sanitary environment, children without EED actually have a faster Kyn synthesis rate, which might be beneficial, because of the cytoprotective and anti-inflammatory functions of downstream metabolites. This study was registered in the Clinical Trials Registry of India as CTRI/2017/02/007921.

Tryptophan Alleviates Acute Heat Stress-Induced Impairment of Antioxidant Status and Mitochondrial Function in Broilers

Heat stress has been considered as a critical risk factor for decreasing performance and causing oxidative stress in broilers. The tryptophan (TRP) derivative 5-hydroxytryptophan has been reported to protect membrane fluidity in broilers suffering from oxidative stress. Therefore, this experiment was conducted to investigate the effects of dietary TRP supplementation on antioxidant status and mitochondrial function-related genes expressions in broilers exposed to acute heat stress (34 ± 1°C, 24 h). Female Arbor Acres broilers (19-d-old, n = 180) were randomly assigned to 1 of 3 treatments. Broilers were fed a basal diet and in the thermoneutral conditions (TN, 23 ± 1°C) was considered as the TN group. Broilers were fed a basal diet and exposed to acute heat stress (HS, 34 ± 1°C) was regarded as the HS group. Broilers were fed a basal diet supplemented with 0.18% L-tryptophan and under HS conditions was treated as the HS + TRP groups. Heat stress led to increased malondialdehyde (MDA) concentration (P < 0.05), while it elevated catalase (CAT), glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), and total antioxidant capacity activities (T-AOC) (P < 0.05) compared with the TN group. Nevertheless, compared with the HS group, TRP supplementation increased SOD activity (P < 0.05). The effects of acute heat stress were associated with increased mRNA abundance for redox-related genes (P < 0.05), and reduced mRNA levels for mitochondrial function-related genes (P < 0.05). Notably, the effects of acute heat stress on mitochondrial function-related genes expressions were reversed by TRP treatment. Collectively, dietary 0.18% TRP supplementation beneficially protects against acute heat stress-induced oxidation stress and mitochondrial dysfunction by regulating antioxidant states and increasing mitochondrial function-related genes expressions in broilers.

Precision intestinal nutrition: knowledge and gaps regarding the role of amino acids during an enteric challenge

Poultry nutritionists continually strive for more “precision” nutritional programs that provide the exact balance of nutrients that maximize broiler growth performance without economically and environmentally costly excesses. Many factors affect the precise amount and balance of nutrients needed by the broiler, including genetics, age, sex, and environment. Furthermore, broilers in intensive rearing environments will almost always be subjected to some degree of enteric stress that can alter nutrient needs. Exposure to enteric pathogens such as Eimeria spp., the intestinal parasites that cause avian coccidiosis, induces physical damage to the intestinal epithelium and activates immune responses, ultimately resulting in the repartitioning of amino acids (AA) in response to these prioritized demands. Even without any pathogenic challenge, the intestine has an already high demand for many AA, with 30 to 100% of dietary AA extracted during first pass intestinal metabolism. In many cases, increasing dietary protein from intact proteins has been shown to be a viable option to ameliorate impaired AA digestion and absorption and heightened need for certain AA of birds under an enteric stress. However, increasing dietary protein often results in concomitant increases in indigestible protein and carbohydrates that can stimulate the overgrowth of pathogenic bacteria (i.e., Clostridium perfringens). Alternative options to increase dietary AA levels are to increase all feed-grade, free AA (e.g., Met, Lys, Thr, Val), or specific individual feed-grade AA. Therefore, the objectives of this paper are to discuss precision nutrition, the dietary AA demands of the intestine, consequences of coccidiosis on AA needs of the intestine, and formulation approaches to meet these altered needs. In summary, increased dietary protein met by intact proteins has consistently demonstrated its benefits during an Eimeria spp. infection; however, to further the goal of precision nutritional programs, feeding higher levels of a specific AA to support desired functions such as intestinal recovery or immune function for birds experiencing an enteric stress still require further evaluation.

Immunomodulatory, behavioral, and nutritional response of tryptophan application on poultry

Tryptophan is an essential amino acid for all animals that was discovered through casein hydrolysis. The use of tryptophan as feed additives has been attracting the attention of many nutritionists because it cannot be synthesized enough in an animal’s body. Tryptophan or precursor to the vitamin niacin in the diet is important, and its supplementation for poultry is determined to improve the amino acid balance and promote the poultry’s growth performance through enhancing appetite, feed efficiency, and protein synthesis. Moreover, poultry in different growth phases, breeding, and conditions require various amounts of tryptophan. In addition, supplemented tryptophan also improves the immune response or the immunomodulatory activity of poultry to various diseases through the kynurenine pathway, especially diseases in the bursa. Furthermore, tryptophan also has a strong relationship with lysine (the ideal tryptophan/lysine ratio) in improving growth performance. However, tryptophan deficiency could affect the behavioral responses (e.g. pecking behavior and poultry stress) because tryptophan serves as a precursor for the neurotransmitter serotonin and the pineal hormone melatonin in the diet. This paper tried to summarize all information about applying tryptophan in the diets and illustrate the roles of tryptophan in the poultry industry.

Systematic Review of the Interaction between Nutrition and Immunity in Livestock: Effect of Dietary Supplementation with Synthetic Amino Acids

Infectious diseases represent one of the most critical threats to animal production worldwide. Due to the rise of pathogen resistance and consumer concern about chemical-free and environmentally friendly productions, the use of antimicrobials drugs is no longer desirable. The close relationship between nutrition and infection has led to numerous studies about livestock. The impact of feeding strategies, including synthetic amino acid supplementation, on host response to various infections has been investigated in different livestock animals. This systematic review provides a synthesis of the experimental studies on the interactions between synthetic amino acid supplementation and immune response to infectious diseases in livestock. Following PRISMA guidelines, quantitative research was conducted using two literature databases, PubMed and Web of Science. The eligibility criteria for the research articles were: (1) the host is a livestock animal; (2) the supplementation with at least one synthetic amino acid; (3) at least one mediator of immunity is measured; (4) at least one production trait is measured. Data were extracted from 58 selected studies. Articles on poultry were the most numerous; few contained experiments using ruminants and pigs. Most of the authors hypothesized that synthetic amino acid supplementation would particularly improve the animals' immune response against intracellular pathogens. An increase in T and natural killer lymphocytes and macrophages activation, intracellular redox state, lymphocytes proliferation and antibodies production were the most described immune mechanisms associated with synthetic amino acid supplementation. Most of the selected studies focused on three amino acids (methionine, threonine and arginine), all of which are associated with a significant improvement of the host immune response. The use of synthetic amino acid supplementation appears as an encouraging perspective for livestock infectious disease management, and research must concentrate on more analytical studies using these three amino acids.

Estimation of dietary tryptophan requirement for laying duck breeders: effects on productive and reproductive performance, egg quality, reproductive organ and ovarian follicle development and serum biochemical indices

This study aimed to determine the dietary tryptophan (Trp) requirement for laying duck breeders. A total of 504 Longyan duck breeders (body weight: 1.20 ± 0.02 kg) aged 22 wk were randomly allocated to 6 treatments, each with 6 replicates of 14 ducks. During the next 16 wk, birds were fed the basal diet with total Trp contents of 1.00, 2.00, 3.00, 4.00, 5.00 and 6.00 g/kg, respectively. Dietary Trp levels increased egg production, egg mass and feed intake of duck breeders from 22 to 37 wk (P < 0.05), and there were linear and quadratic effects of Trp level (P < 0.05). The feed conversion ratio (FCR) quadratically decreased with dietary Trp levels (P < 0.05). Dietary Trp levels decreased (P < 0.05) egg albumen height and Haugh unit at wk 8 or 12, and the responses were linear and quadratic (P < 0.05). The body weight of breeders, absolute and relative weight of oviduct, number and total weight of preovulatory follicles (POF), and its proportion relative to ovarian weight were increased (P < 0.05), and the responses were linear (P < 0.01) and quadratic (P < 0.001). Ovarian weight increased quadratically (P < 0.05), and the mean weight of POF increased (P < 0.05), linearly and quadratically. The proportion of small yellow follicles relative to ovary weight decreased (P < 0.01) linearly and quadratically. At wk 16 of the trial period, the serum albumin content and alanine aminotransferase activity decreased (P < 0.05) and the creatinine content increased (P < 0.01) linearly and quadratically. The Trp requirements were estimated to be 3.14 g/kg for optimizing egg production, 2.93 g/kg for egg mass, and 2.92 g/kg for FCR. Overall, dietary Trp levels (1 to 6 g/kg) affected productive performance, egg quality, reproductive organ and ovarian follicle development, and serum biochemical indices of layer duck breeders, and a diet containing 2.9 to 3.1 g Trp per kg feed was adequate during the laying period (22 to 37 wk of age).

Tryptophan in poultry nutrition: Impacts and mechanisms of action

Many studies have shown that productivity, immune system, antioxidant status, and meat and egg quality can be optimized by dietary supplementation with amino acids that are not usually added to poultry diets. Understanding the effects of these amino acids may encourage feed manufacturers and poultry producers to include them as additives. One of these amino acids is tryptophan (Trp). The importance of Trp is directly related to its role in protein anabolism and indirectly related to its metabolites such as serotonin and melatonin. Thus, Trp could affect the secretion of hormones, development of immune organs, meat and egg production, and meat and egg quality in poultry raised under controlled or stressed conditions. Therefore, this review discusses the main roles of Trp in poultry production and its mode (s) of action in order to help poultry producers decide whether they need to add Trp to poultry diets. Further areas of research are also identified to address information gaps.

Amino Acid Nutrition and Metabolism in Chickens

Both poultry meat and eggs provide high-quality animal protein [containing sufficient amounts and proper ratios of amino acids (AAs)] for human consumption and, therefore, play an important role in the growth, development, and health of all individuals. Because there are growing concerns about the suboptimal efficiencies of poultry production and its impact on environmental sustainability, much attention has been paid to the formulation of low-protein diets and precision nutrition through the addition of low-cost crystalline AAs or alternative sources of animal-protein feedstuffs. This necessitates a better understanding of AA nutrition and metabolism in chickens. Although historic nutrition research has focused on nutritionally essential amino acids (EAAs) that are not synthesized or are inadequately synthesized in the body, increasing evidence shows that the traditionally classified nutritionally nonessential amino acids (NEAAs), such as glutamine and glutamate, have physiological and regulatory roles other than protein synthesis in chicken growth and egg production. In addition, like other avian species, chickens do not synthesize adequately glycine or proline (the most abundant AAs in the body but present in plant-source feedstuffs at low content) relative to their nutritional and physiological needs. Therefore, these two AAs must be sufficient in poultry diets. Animal proteins (including ruminant meat & bone meal and hydrolyzed feather meal) are abundant sources of both glycine and proline in chicken nutrition. Clearly, chickens (including broilers and laying hens) have dietary requirements for all proteinogenic AAs to achieve their maximum productivity and maintain optimum health particularly under adverse conditions such as heat stress and disease. This is a paradigm shift in poultry nutrition from the 70-year-old "ideal protein" concept that concerned only about EAAs to the focus of functional AAs that include both EAAs and NEAAs.

Effect of dietary tryptophan supplementation on growth performance, immune response and anti-oxidant status of broiler chickens from 7 to 21 days

Background

This study was conducted to investigate the optimum dietary level of tryptophan (Trp) supplementation at which broiler chickens have better growth with efficient immune system and anti‐oxidant status.

Method

One hundred and twenty (n = 120) 1‐day‐old broiler chicks were fed a common commercial diet from days 1 to 7. On day 7, the chicks were randomly divided in three treatment groups, that is, Trp 0.2 [national research council (NRC) recommended level of tryptophan], Trp 0.3 (tryptophan supplemented at 0.3%) and Trp 0.5 (tryptophan supplemented at 0.5%). All the experimental diets were iso‐caloric (ME; 3,000 kcal/kg) and iso‐proteic (CP; 18.5%). Weekly data on feed intake and body weight gain (BWG) were recorded to calculate feed conversion ratio (FCR). On day 19, avian tuberculin was injected to note the cellular immunity. On day 21, two birds per replicate were killed to determine carcass and visceral organ weights. Blood serum samples were collected for analysis of humoral immune response against sheep red blood cells, total oxidant and anti‐oxidants by spectrophotometric method.

Results

Feed intake, carcass and visceral organ weights remained unaffected by dietary treatments while BWG and FCR tended to improve (p < .05) in broiler chicks fed the Trp 0.3 and the Trp 0.5 diets. Total oxidant status was also improved (p < .05) in broiler chicks fed the Trp 0.5 diet. Likewise, broiler chicks fed the Trp 0.3 and the Trp 0.5 diets tended to have better (p < .05) total anti‐oxidant status, catalase, glutathione peroxidase, glutathione reductase and arylesterase (ARE). The overall antibodies response and IgG improved (p < .05) by the Trp 0.3 and Trp 0.5 diets compared to control. However, IgM level remained similar across the treatment. The cellular immunity against avian tuberculin improved at 24 hr post‐injection but its effect disappeared at 48 hr.

Conclusion

The results of present study revealed that Trp above the NRC recommended level may give better growth, immune response and anti‐oxidant status in broiler chickens.