Influence of L-threonine supplementation on goblet cell numbers, histological structure and antioxidant enzyme activities of laying hens reared in a hot and humid climate

Alleviative Effect of Threonine on Cadmium-Induced Liver Injury in Mice

As a toxic trace element commonly found in food, cadmium (Cd) can cause severe liver injury. Our previous study showed that threonine (Thr) could significantly alleviate Cd toxicity in yeast. To investigate the effect of Thr on Cd-induced liver injury in mice, twenty-four mice were randomly divided into four groups: control, Cd, and low/high dose of Thr-treatment groups (0.04 and 0.08 mmol/kg/day, respectively). After 7 days of continuous treatment, the alleviative effect of Thr on liver injury in Cd-exposed mice was assessed. The results showed that Thr significantly reduced the elevation of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in Cd-exposed mice. Histological analysis showed that Thr decreased Cd-induced hepatic steatosis, zonal necrosis, and inflammatory cell infiltration. Thr also reduced the Cd-induced malondialdehyde (MDA) and O^2- levels and restored superoxide dismutase (SOD) and catalase (CAT) activities in the liver. Further investigation showed that Thr significantly suppressed Cd-induced inflammatory response (tumor necrosis factor-α and interleukin-6) and restored the level of anti-apoptotic protein (Blc-2) but inhibited the elevation of pro-apoptotic proteins (Bax and caspase-3), as well as the activation of the PI3K/AKT signaling pathway in Cd-exposed mice. In conclusion, Thr alleviated Cd-induced liver injury through reducing Cd-induced oxidative stress, inflammation, and attenuating hepatocyte apoptosis via PI3K/AKT-related signaling pathway.

A review of heat stress in chickens. Part II: Insights into protein and energy utilization and feeding

With the growing global demand for animal protein and rising temperatures caused by climate change, heat stress (HS) is one of the main emerging environmental challenges for the poultry industry. Commercially-reared birds are particularly sensitive to hot temperatures, so adopting production systems that mitigate the adverse effects of HS on bird performance is essential and requires a holistic approach. Feeding and nutrition can play important roles in limiting the heat load on birds; therefore, this review aims to describe the effects of HS on feed intake (FI) and nutrient digestibility and to highlight feeding strategies and nutritional solutions to potentially mitigate some of the deleterious effects of HS on broiler chickens. The reduction of FI is one of the main behavioral changes induced by hot temperatures as birds attempt to limit heat production associated with the digestion, absorption, and metabolism of nutrients. Although the intensity and length of the heat period influences the type and magnitude of responses, reduced FI explains most of the performance degradation observed in HS broilers, while reduced nutrient digestibility appears to only explain a small proportion of impaired feed efficiency following HS. Targeted feeding strategies, including feed restriction and withdrawal, dual feeding, and wet feeding, have showed some promising results under hot temperatures, but these can be difficult to implement in intensive rearing systems. Concerning diet composition, feeding increased nutrient and energy diets can potentially compensate for decreased FI during HS. Indeed, high energy and high crude protein diets have both been shown to improve bird performance under HS conditions. Specifically, positive results may be obtained with increased added fat concentrations since lipids have a lower thermogenic effect compared to proteins and carbohydrates. Moreover, increased supplementation of some essential amino acids can help support increased amino acid requirements for maintenance functions caused by HS. Further research to better characterize and advance these nutritional strategies will help establish economically viable solutions to enhance productivity, health, welfare, and meat quality of broilers facing HS.

Physiological Functions of Threonine in Animals: Beyond Nutrition Metabolism

Threonine (Thr), an essential amino acid for animals and the limiting amino acid in swine and poultry diets, which plays a vital role in the modulation of nutritional metabolism, macromolecular biosynthesis, and gut homeostasis. Current evidence supports that the supplementation of Thr leads to benefits in terms of energy metabolism. Threonine is not only an important component of gastrointestinal mucin, but also acts as a nutritional modulator that influences the intestinal immune system via complex signaling networks, particularly mitogen-activated protein kinase (MAPK) and the target of the rapamycin (TOR) signal pathway. Threonine is also recognized as an indispensable nutrient for cell growth and proliferation. Hence, optimization of Thr requirement may exert a favorable impact on the factors linked to health and diseases in animals. This review focuses on the latest reports of Thr in metabolic pathways and nutritional regulation, as well as the relationship between Thr and relevant physiological functions.

Effects of Dietary Valine Levels on Production Performance, Egg Quality, Antioxidant Capacity, Immunity, and Intestinal Amino Acid Absorption of Laying Hens during the Peak Lay Period

The present study aimed to assess the impact of dietary valine levels on layer production performance, egg quality, immunity, and intestinal amino acid absorption of laying hens during the peak lay period. For this purpose, a total of 960 33-week-old Fengda No.1 laying hens were randomly divided into five experimental groups and fed with valine at the following different levels in a feeding trial that lasted 8 weeks: 0.59, 0.64, 0.69, 0.74, and 0.79%, respectively. Productive performances were recorded throughout the whole rearing cycle and the egg quality, serum indexes, and small intestine transporters expression were assessed at the end of the experiment after slaughter (41 weeks) on 12 hens per group. Statistical analysis was conducted by one-way ANOVA followed by LSD multiple comparison tests with SPSS 20.0 (SPSS, Chicago, IL, USA). The linear and quadratic effects were tested by SPSS 20.0. Egg mass, laying rate, broken egg rate, and feed conversion ratio were significantly improved with increasing dietary valine levels. However, the egg weight, eggshell thickness, albumen height, Haugh unit, and egg yolk color were significantly decreased with increasing dietary valine levels. Serum catalase (CAT), immunoglobulin A (IgA) and IgM levels, and malondialdehyde (MDA) levels were negative responses to valine-treated laying hens. Dietary supplemented valine enhanced the trypsin activity of duodenum chime and promoted the mRNA expression levels of ATB0,+, and LAT4 in the jejunum and corresponding serum free Ile, Lys, Phe, Val, and Tyr level. However, valine treatment significantly downregulated the mRNA expression levels of PePT1, B0AT1, LAT1, and SNAT2 in the small intestines and corresponding serum free Arg, His, Met, Thr, Ala, Asp, Glu, Gly, and Ser level. Our results suggest that 0.79% valine dietary supplementation can improve production performance by promoting amino acid nutrient uptake and utilization, and suggest a supplement of 0.79% valine to diet.

Intestinal Health and Threonine Requirement of Growing Pigs Fed Diets Containing High Dietary Fibre and Fermentable Protein

Simple Summary

Dietary components, such as fibre and protein, have significant impacts on nutrient requirements and intestinal health in pigs. The objectives of this study were to investigate the interactive effects of dietary fibre and fermentable protein on threonine requirement for protein deposition in growing pigs and to determine how these factors affect markers of intestinal health. In this study we used the nitrogen-balance approach to study the influence of high protein diets combined with high fibre on threonine requirement for protein deposition. We further used gene expression, fermentation metabolites (short and branched chain fatty acid concentration), and serum antioxidant status in these pigs as markers of intestinal health and function. We demonstrate that high fibre will indeed increase threonine requirement for protein deposition but can mitigate the negative effects of fermentable protein metabolites on intestinal health. These results will have implications for the development of dietary strategies to improve growth and overall health in pigs, including adjustments to dietary fibre, protein, and amino acid content that maximize pig growth, nutrient utilization, and intestinal health.

Abstract

Dietary fibre (DF) and fermentable crude protein (fCP) are dietary factors which affect nutrient utilization and intestinal health in pigs. A nitrogen (N)-balance study was conducted to determine the impact of DF and fCP on threonine (Thr) requirement for protein deposition (PD) and indicators of intestinal health. A total of 160 growing pigs (25 kg) were randomly assigned to 1 of 20 dietary treatments in a 2 × 2 × 5 factorial arrangement in a randomized complete block design with dietary fibre (low (LF) or high fibre (HF)], fCP [low (LfCP) or high fCP (HfCP)) and Thr (0.52, 0.60, 0.68, 0.76, or 0.82% standardized ileal digestible) as factors. Then, 4-day total urine and fecal collection was conducted, and pigs were euthanized for intestinal tissue and digesta sampling. Feeding high DF, regardless of fCP content, increased Thr requirement for PD (p < 0.05). High fCP, regardless of DF content, reduced Thr requirement for PD. Serum antioxidant capacity increased as dietary Thr level increased (p < 0.05). Cecal digesta short-chain fatty acids (SCFA) increased (p < 0.05) with HF and branched-chain fatty acids (BCFA) increased with HfCP and reduced with HF (p < 0.05). HfCP reduced (p < 0.05) mucin-2 (MUC2) expression in the colon of the HF but not the LF fed pigs and HF increased MUC2 in the LfCP but not the HfCP fed pigs. Feeding HF diet increased (p < 0.05) expression of zonula occludens-1 in the LfCP with no effect on HfCP fed pigs. Ammonia concentration in both cecum and colon increased (p < 0.05) in the HfCP fed pigs. Overall, high DF reduced the negative impact of HfCP on intestinal health, as indicated by alterations in SCFA and BCFA production and gut barrier gene expression. While increased dietary Thr content is required for PD in pigs fed high DF, feeding high fCP reduced Thr requirements.

Effect of dietary fiber and threonine content on intestinal barrier function in pigs challenged with either systemic E. coli lipopolysaccharide or enteric Salmonella Typhimurium

Background

The independent and interactive effects of dietary fiber (DF) and threonine (Thr) were investigated in growing pigs challenged with either systemic E. coli lipopolysaccharide (LPS) or enteric Salmonella Typhimurium (ST) to characterise their effect on intestinal barrier function.

Results

In experiment 1, intestinal barrier function was assessed via oral lactulose and mannitol (L:M) gavage and fecal mucin analysis in pigs challenged with E. coli LPS and fed low fiber (LF) or high fiber (HF) diets with graded dietary Thr. Urinary lactulose recovery and L:M ratio increased (P < 0.05) during the LPS inoculation period in LF fed pigs but not in HF fed pigs. Fecal mucin output was increased (P < 0.05) in pigs fed HF compared to LF fed pigs. In experiment 2, RT-qPCR, ileal morphology, digesta volatile fatty acid (VFA) content, and fecal mucin output were measured in Salmonella Typhimurium challenged pigs, fed LF or HF diets with standard or supplemented dietary Thr. Salmonella inoculation increased (P < 0.05) fecal mucin output compared to the unchallenged period. Supplemental Thr increased fecal mucin output in the HF-fed pigs (Fib × Thr; P < 0.05). Feeding HF increased (P < 0.05) VFA concentration in cecum and colon. No effect of either Thr or fiber on expression of gene markers was observed except a tendency (P = 0.06) for increased MUC2 expression with the HF diet. Feeding HF increased goblet cell numbers (P < 0.05).

Conclusion

Dietary fiber appears to improve barrier function through increased mucin production capacity (i.e., goblet cell numbers, MUC2 gene expression) and secretion (i.e., fecal mucin output). The lack of effect of dietary Thr in Salmonella-challenged pigs provides further evidence that mucin secretion in the gut is conserved and, therefore, Thr may be limiting for growth under conditions of increased mucin production.

Efficacy of ajwain (Trachyspermum ammi L.) seed at graded levels of dietary threonine on growth performance, serum metabolites, intestinal morphology and microbial population in broiler chickens

The present study investigated the influence of dietary threonine (Thr) levels and ajwain seed (AS) on the growth performance, immunity, blood metabolites, ileal microflora and jejunum morphology of broiler chickens. A total of 600-day-old male broiler chickens (Ross 308) were randomly allocated among five replicates of eight dietary treatments according to a 4 × 2 factorial arrangement of treatments, including four different levels of Thr (100, 105, 110 and 115% of requirements) and two inclusion rates of AS (0 or 10 g/kg of the diet). Body weight gain and FCR improved in broiler chickens fed 105% Thr supplement during the starter, finisher and whole periods of the experiment (p < .05). The broiler chickens fed AS supplemented diet had a greater weight gain (25-42 days) and better FCR (1-10 and 25-42 days) than those without AS (p < .05). A significant interaction was observed between Thr and AS supplementation for lymphocyte, heterophil/lymphocyte (H/L), bursa and spleen (p < .05). The liver enzyme activity of aspartate aminotransferase (AST) was higher in the chicks that received diet without AS supplement than those fed AS diet (p < .05). Inclusion of 105% dietary Thr and 10 g/kg AS increased the viable cell counts of Lactobacilli and decreased the population of the Escherichia coli in broilers (p < .05). In jejunum morphology, the broiler chickens fed 105% Thr diet had a greater villus length, width and crypt depth (p < .05). Also, the villus length was longer in broilers that received AS supplemented diet (p < .05). It is concluded that the dietary 105% of Thr and AS supplement individually improved growth performance, ileal microbial population and jejunum morphology of broiler chickens.

Effects of the Methionine Hydroxyl Analogue Chelate Zinc on Antioxidant Capacity and Liver Metabolism Using 1H-NMR-Based Metabolomics in Aged Laying Hens

Simple Summary

Zinc, an essential trace element for laying hens, plays an important role in biological processes, such as growth, tissue growth and repairment, skeletal development, and immune competence, which also has better effects on growth performance, biochemical indexes, and antioxidant capacity. Our previous work has shown that methionine hydroxyl analogue chelated zinc (MHA-Zn) has better effects on eggshell quality, the apparent retention of minerals and nutrients, trace element deposit, and metallothionein (MT) mRNA expression. The objective of the current study was to investigate the effects of different levels of MHA-Zn on antioxidant capacity and liver metabolism of aged laying hens. The results suggest that dietary supplementation of MHA-Zn levels at 80 mg/kg has better effects on antioxidant capacity and liver metabolism, as well as homeostasis of the body.

Abstract

This study aimed to investigate the effects of different levels of methionine hydroxyl analogue chelated zinc (MHA-Zn) on antioxidant capacity and liver metabolism of aged laying hens. A total of 960 57-week-old layers were fed a basal diet (Zn: 35.08 mg/kg) without extra zinc for two weeks, and then allocated to four treatments consisting of eight replicates of 30 birds each for 14 weeks. Four levels of Zn (zinc sulfate (ZnSO₄): 80 mg/kg; MHA-Zn: 20, 40, 80 mg/kg) were added to the diet. The results indicated that compared with inorganic zinc, organic zinc of 80 mg/kg has a significant advantage in improving the antioxidant capacity of aged hens, which increased the level of Cu/Zn-superoxide dismutase (SOD) and the total antioxidant capacity (T-AOC) in the serum and liver, and reduced the concentration of malondialdehyde (MDA) of laying hens. The serum albumen composition was significantly modified, meanwhile, the level of total protein, globulin, and urea increased remarkably, whereas serum glutamic-oxaloacetic transaminase decreased notably in 80 mg/kg MHA-Zn groups. Compared with the 20 mg/kg MHA-Zn group, the metabolic profile of 40 and 80 mg/kg MHA-Zn groups was higher than that of the inorganic zinc group. Furthermore, integrated key metabolic pathway analysis showed that 40 and 80 mg/kg MHA-Zn groups participated in the regulation of glutathione metabolism, glycine, serine, and threonine metabolism. Therefore, this study suggests that 40 and 80 mg/kg supplementation of MHA-Zn can increase the activity of Cu/Zn-SOD and T-AOC and decrease MDA; additionally the 80 mg/kg MHA-Zn group has better antioxidant capacity. Meanwhile, the enhanced MHA-Zn promoted methionine (Met) synthesis and protein metabolism.

Effects of Dietary Threonine Levels on Intestinal Immunity and Antioxidant Capacity Based on Cecal Metabolites and Transcription Sequencing of Broiler

Simple Summary

Threonine (Thr), an indispensable amino acid for animals and the third limiting amino acid of broilers, plays a vital role in the synthesis of gut mucosal proteins, which also has better effects on growth performance, biochemical indexes, antioxidant function, and gut morphology, as well as acting as a nutrient immunomodulator that affects the intestinal barrier function of broilers. However, it is not clear how it works in depth. The objective of the current study was to investigate the mechanism of effects of different dietary threonine levels on the antioxidant and immune capacity of broilers. Our findings suggest that a Thr level of 125% NRC (Nutrient Requirements of Poultry, 1994) recommendations had better effects on antioxidant and immune capacity, including resisting viruses and decreasing the abnormal proliferation of cells. As well as this, it also had better effects on maintaining the homeostasis of the body.

Abstract

This study aimed to determine the effects of different dietary threonine levels on the antioxidant and immune capacity and the immunity of broilers. A total of 432 one-day-old Arbor Acres (AA) broilers were randomly assigned to 4 groups, each with 6 replicates of 18 broilers. The amount of dietary threonine in the four treatments reached 85%, 100%, 125%, and 150% of the NRC (Nutrient Requirements of Poultry, 1994) recommendation for broilers (marked as THR85, THR100, THR125, and THR150). After 42 days of feeding, the cecum contents and jejunum mucosa were collected for metabolic analysis and transcriptional sequencing. The results indicated that under the condition of regular and non-disease growth of broilers, compared with that of the THR85 and THR150 groups, the metabolic profile of the THR125 group was significantly higher than that of the standard requirement group. Compared with the THR100 group, the THR125 group improved antioxidant ability and immunity of broilers and enhanced the ability of resisting viruses. The antioxidant gene CAT was upregulated. PLCD1, which is involved in immune signal transduction and plays a role in cancer suppression, was also upregulated. Carcinogenic or indirect genes PKM2, ACY1, HK2, and TBXA2 were down-regulated. The genes GPT2, glude2, and G6PC, which played an important role in maintaining homeostasis, were up-regulated. Therefore, the present study suggests that 125% of the NRC recommendations for Thr level had better effects on antioxidant and immune capacity, as well as maintaining the homeostasis of the body.

Threonine Requirements in Dietary Low Crude Protein for Laying Hens under High-Temperature Environmental Climate

Simple Summary

The threonine (Thr) requirement of laying hens in a high-temperature climate is scarcely referred in the review of literature. Therefore, our aim was to estimate the dietary Thr requirement in low CP diets in a high-temperature environmental climate. Based on our findings, the optimal dietary Thr requirements to optimize egg production, serum uric acid, and serum CuZn-SOD were 0.58%, 0.59%, and 0.56%, respectively, by regression analysis.

Abstract

Lohmann Brown hens (n = 420), at 28 weeks of age, were divided into five dietary treatments, and each treatment included six replicates of 14 laying hens. Dietary crude protein (14%) was presented as the control diet. Dietary L-Thr was added to the control diet for 12 weeks. Dietary Thr levels are 0.43%, 0.49%, 0.57%, 0.66%, and 0.74%, based on digestible base. From 28 to 40 weeks, hen-day egg production presented a quadratic trend to supplementing dietary Thr (R² = 0.96, p = 0.02), and reached a maximum level at 0.58%. Serum uric acid demonstrated a quadratic trend (R² = 0.62, p = 0.02) at 0.59%. Both serum total cholesterol and 3-hydroxy-3-methylglutaryl (HMG-CoA) reductase showed lower levels (p < 0.05) at 0.66% Thr. Serum CuZn-SOD elevated (p < 0.05) at 0.49%, 0.57%, and 0.66% Thr, as compared to the control group, and showed a quadratic trend (R² = 0.87, p = 0.003) at 0.56%. Supplemental L-Thr decreased (p < 0.05) the expression of ileal HSP70 at 0.66% Thr. In summary, the optimal dietary Thr requirements to optimize egg production, serum uric acid, and serum CuZn-SOD were 0.58%, 0.59%, and 0.56%, respectively, by regression analysis.

Threonine in broiler diets: an updated review

Threonine (Thr) is the third limiting essential amino acid after methionine and lysine in cornsoybean based diets of broilers. Dietary imbalance of Thr, therefore, results in a poor growth performance in broilers. This review summarizes literature data on the known effects of dietary levels of Thr on growth performance, gut morphology, immunity and carcass characteristics in broilers. Due to continuous improvement in genetic potential and management practices for poultry production, dietary Thr requirements are changing. A number of studies have shown that supplementation of Thr in broiler diet at a higher level than the current NRC recommendation (0.74-0.81%), increases body weight gain, feed conversion ratio, and improves gut morphology, carcass quality and immune status, mainly by enhancing the functional capability of digestive system and immune organs (spleen, bursa, and thymus). According to the literature data discussed in this review, the minimal and maximal total dietary Thr levels for healthy birds reared in normal conditions were 0.67 and 0.90% for growth performance, 0.77 and 1.1% for a better gut health, 0.60 and 1.02% for immunity and 0.62 and 0.97% for better carcass characteristics. This background provides impetus to further investigate the exact level of Thr and its effects on growth performance, gut morphology, immunity and carcass characteristics in broilers.

Effects of dietary threonine and immune stress on growth performance, carcass trait, serum immune parameters, and intestinal muc2 and NF-κb gene expression in Pekin ducks from hatch to 21 days

An experiment was conducted to investigate the effects of different dietary threonine (Thr) levels and immune stress on Pekin ducklings' growth performance, carcass traits, serum immune parameters, and intestinal mucin 2 (MUC2) and nuclear factor kB (NF-κB) gene expressions. A total of 320 Pekin ducklings was randomly assigned to a 5 × 2 factorial arrangement of treatments. Each treatment group consisted of 4 replicate pens with 8 ducks per pen. Ducklings were fed 5 graded levels of Thr: 0.49, 0.56, 0.60, 0.65, and 0.76% from hatch to 21 d of age. At 11 d of age, ducks in the stressed groups were challenged with bovine serum albumin (BSA), and ducks in the unstressed groups were injected with normal saline water. The results showed that increasing Thr supplementation from 0.49 to 0.56% in the diet can improve BWG; feed consumption; weight and relative weight of breast and leg; weight of liver, bursa of Fabricius, spleen, and thymus; serum natural immune globulin A (IgA) concentration; and MUC2 gene expression in the ileum of 21-day-old Pekin ducks, significantly (P < 0.05). Immune stress with BSA had a significant effect on 21-day-old Pekin ducklings' BWG, feed consumption, and weight and relative weight of breast and thymus (P < 0.05), but no interaction between BSA and dietary Thr content was noticed in our experiment in 21-day-old Pekin ducks (P < 0.05). Dietary Thr requirements of the unstressed groups and stressed groups based on broken-line model analyses for ducks' BWG were 0.705 and 0.603%, respectively, and for ducks' feed consumption were 0.724 and 0.705%, respectively.

Effects of dietary threonine levels on growth performance, serum biochemical indexes, antioxidant capacities, and gut morphology in broiler chickens

A dose-response experiment was conducted to investigate the impacts of dietary threonine (Thr) levels on growth performance, serum biochemical indices, antioxidant capacities, and gut morphology of broiler chickens. Four hundred and thirty-two 1-d-old commercial broilers were allocated to 4 treatments consisting of 6 replicates of 18 birds. The experimental treatments received the same Thr-deficient basal diet and were labeled as follows: 85%, 100%, 125%, and 150% of NRC (1994) recommendations. The results demonstrated that on 21 d and 42 d, average daily weight gain (ADG, 22 to 42 d, 0 to 42 d) increased quadratically or cubically as the inclusion of Thr increased, while feed conversion ratio (FCR, 0 to 21 d, 0 to 42 d) decreased quadratically or cubically as dietary Thr increase from 85% to 150%. Excess dietary Thr levels triggered plasma aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities. The concentrations of total protein (TP) and globulin (GLO) increased quadratically with increasing Thr level, and the highest concentrations of TP and GLO were obtained at the 125% Thr level. Moreover, the plasma uric acid (UA) concentration decreased linearly or quadratically with the increase in dietary Thr level. Likewise, the serum glutathione peroxidase (GSH-Px) and total superoxide dismutases (T-SOD) activities increased quadratically as dietary Thr increased, and the highest activity of GSH-Px was obtained at the 125% Thr level, while the highest T-SOD level occurred in the 100% Thr group. Gut morphology of birds showed significant response to different graded concentrations of Thr level. Villus height (VH), crypt depth (CD), and VH:CD ratio (VH/CD) were increased linearly or quadratically by Thr supplementation. Therefore, the present study suggests that the NRC (1994) recommendations Thr level that was optimum for growth performance, and 125% of the NRC (1994) recommendations Thr level had better effects on biochemical indices, antioxidant function, and gut morphology of broilers.

Effects of threonine supplementation on the growth performance, immunity, oxidative status, intestinal integrity, and barrier function of broilers at the early age

The aim of this study was to investigate effects of L-threonine (L-Thr) supplementation on the growth performance, immunity, antioxidant status, and intestinal health of broilers at the early age. One hundred and forty-four 1-day-old male broiler chicks (Arbor Acres Plus) were allocated into 3 treatments with 6 replicates of 8 birds each, and fed a basal diet (analyzed Thr content, 7.87 g/kg) supplemented with 0 (control diet), 1 and 3 g/kg L-Thr for 21 d, respectively. Treatments did not alter growth performance of broilers. Compared with control, 1 g/kg Thr supplementation increased relative weight of spleen (P = 0.013). A higher level of Thr (3 g/kg) increased relative weight of thymus (P = 0.003). The supplementation of 3 g/kg Thr reduced Escherichia coli (P = 0.040) and Salmonella colonies (P = 0.015), whereas increased Lactobacillus colonies (P < 0.001) in the cecal contents. Thr supplementation increased intestinal villus height (P < 0.05), and the ratio of villus height to crypt depth (P < 0.001), and the values for these parameters were intermediate with 1 g/kg Thr. Goblet cell density was increased by Thr supplementation (P < 0.001). The jejunal immunoglobulin G content was increased by the inclusion of Thr (P = 0.002). Broilers fed diet supplemented with 1 g/kg Thr exhibited increased concentrations of jejunal immunoglobulin M (P = 0.037) and secretory immunoglobulin A (P = 0.018). Likewise, 3 g/kg Thr inclusion increased ileal secretory immunoglobulin A content (P = 0.023). The jejunal malondialdehyde accumulation was reduced by Thr inclusion (P = 0.012). A higher level of Thr inclusion also reduced malondialdehyde content in the serum (P = 0.029). The high level of Thr inclusion (3 g/kg) upregulated mucin-2 mRNA expression (P = 0.034), whereas downregulated the mRNA abundances of interferon-γ (P = 0.036) and interleukin-1β (P = 0.031) in the ileum. In conclusion, L-Thr supplementation can improve immunity, antioxidant capacity, and intestinal health of broilers at an early age.

Effect of dietary threonine on laying performance and intestinal immunity of laying hens fed low-crude-protein diets during the peak production period

Threonine (Thr) may be a limiting amino acid for laying hens fed diets with lowered protein level. An experiment was conducted to examine laying performance, and the intestinal immune function of laying hens provided diets varying in digestible Thr levels. Lohmann Brown laying hens (n = 480), 28 weeks of age, were allocated to six dietary treatments, each of which included five replicates of 16 hens. Dietary crude protein (CP) 16.18% diet was offered as the positive control diet. L-Thr was added to the negative diet (14.16% CP) by 0, 1.0, 2.0, 3.0 and 4.0 g/kg, corresponding 0.44%, 0.43%, 0.49%, 0.57%, 0.66% and 0.74% digestible Thr. At 40 weeks, a reduction in CP level decreased laying performance (p < 0.05). In the low CP, increasing dietary Thr increased (p < 0.05) egg production and egg mass and rose to a plateau between 0.57% and 0.66%. The hens fed 0.66% Thr showed the lowest value (p < 0.05) of feed conversion ratio (FCR). Serum level of uric acid showed the lowest values (p < 0.05) at 0.57-0.66%. In addition, serum-free Thr maximized (p < 0.05) between 0.66% and 0.74%. Digestive trypsin activity decreased (p < 0.05) when hens fed the low-CP diet compared with hens fed CP (16.18%) and hens fed 0.57-0.66%. Expressions of ileal MUC2 mRNA maximized (p < 0.05) at 0.66% Thr. Occludin mRNA increased with increasing Thr level (p < 0.05). sIgA mRNA reached to the maximum level (p < 0.05) at 0.66% and 0.74% Thr. INF-γ mRNA reached to the lowest level (p < 0.05) at 0.65%. Expressions of ileal IL-2, IL-6, IL-1β mRNA decreased with increasing Thr level (p < 0.05). In conclusion, Thr supplementation resulting in optimal laying performance and stimulated the mucosal immune system, suggesting that it is a limiting amino acid in the low-crude-protein diet of laying hens during the peak production period.

Effect of excess dietary L-valine on laying hen performance, egg quality, serum free amino acids, immune function and antioxidant enzyme activity

1. The aim of this study was to evaluate the tolerance of laying hens for an excessive L-valine (L-val) supply on laying performance, egg quality, serum free amino acids, immune function and antioxidant enzyme activities of laying hens. 2. A total of 720 HyLine Brown hens were allocated to 5 dietary treatment groups, each of which included 6 replicates of 24 hens, from 40 to 47 weeks of age. Graded amounts of L-val were added to the basal diet to achieve concentrations of 0 (control), 1, 2, 3 and 4 g/kg, respectively, in the experimental diets. 3. Supplementing the diet with L-val did not affect egg production, egg mass, egg weight, feed conversion ratio (FCR) or egg quality. The average daily feed intake response to supplemental L-val was quadratic and was maximised at 2.0 g L-val/kg diet. No differences were observed for total protein, total amino acids, blood urea nitrogen (BUN), uric acid, lactate dehydrogenase (LDH), alkaline phosphatase (AKP), Ca and P concentrations among the treatments. 4. Serum albumin concentration increased significantly in response to supplemental L-val and was also maximised at 2.0 g/kg. In addition, serum glucose increased quadratically to peak at 2.0 g L-val/kg diet. Serum free valine increased as L-val concentration increased to 2.0 g/kg diet and then decreased linearly. 5. Supplementation of L-val did not affect the serum concentrations of total antioxidative capability (T-AOC), superoxide dismutase (SOD) and malondialdehyde (MDA). L-val supplementation did not affect the concentrations of immunoglobulins IgG, IgA, IgM and complements (C3 and C4). Serum concentration of triiodothyronine (T3) increased significantly at 2.0 g L-val/kg diet. 6. It is concluded that high concentrations of L-val are tolerated and can be successfully supplemented into diets without detrimental effects on laying performance or immune function of laying hens.