Heat as a stressor of poultry has been studied extensively for many decades; it affects poultry production on a worldwide basis and has significant impact on well-being and production. More recently, the involvement of heat stress in inducing oxidative stress has received much interest. Oxidative stress is defined as the presence of reactive species in excess of the available antioxidant capacity of animal cells. Reactive species can modify several biologically cellular macromolecules and can interfere with cell signaling pathways. Furthermore, during the last decade, there has been an ever-increasing interest in the use of a wide array of natural feed-delivered phytochemicals that have potential antioxidant properties for poultry. In light of this, the current review aims to (1) summarize the mechanisms through which heat stress triggers excessive superoxide radical production in the mitochondrion and progresses into oxidative stress, (2) illustrate that this pathophysiology is dependent on the intensity and duration of heat stress, (3) present different nutritional strategies for mitigation of mitochondrial dysfunction, with particular focus on antioxidant phytochemicals. Oxidative stress that occurs with heat exposure can be manifest in all parts of the body; however, mitochondrial dysfunction underlies oxidative stress. In the initial phase of acute heat stress, mitochondrial substrate oxidation and electron transport chain activity are increased resulting in excessive superoxide production. During the later stage of acute heat stress, down-regulation of avian uncoupling protein worsens the oxidative stress situation causing mitochondrial dysfunction and tissue damage. Typically, antioxidant enzyme activities are upregulated. Chronic heat stress, however, leads to downsizing of mitochondrial metabolic oxidative capacity, up-regulation of avian uncoupling protein, a clear alteration in the pattern of antioxidant enzyme activities, and depletion of antioxidant reserves. Some phytochemicals, such as various types of flavonoids and related compounds, were shown to be beneficial in chronic heat-stressed poultry, but were less or not effective in non-heat-stressed counterparts. This supports the contention that antioxidant phytochemicals have potential under challenging conditions. Though substantial progress has been made in our understanding of the association between heat stress and oxidative stress, the means by which phytochemicals can alleviate oxidative stress have been sparsely explored.

This trial was conducted to evaluate the effects of dietary supplementation of phytogenic product containing an equal mixture of thymol and carvacrol at 4 levels (0, 60, 100, and 200 mg/kg of diet) on performance, antioxidant enzyme activities, fatty acid composition, digestive enzyme activities, and immune response in broiler chickens. Each of the 4 diets was fed to 5 replicates of 12 chicks each from d 0 to 42. The inclusion of thymol + carvacrol linearly decreased (P < 0.05) feed intake, but the highest (P < 0.05) BW gain (ADG) and feed efficiency was observed in broilers offered 200 mg/kg of phytogenic product. The phytogenic product linearly increased (P < 0.05) superoxide dismutase and glutathione peroxidase activities and decreased (P < 0.05) malondialdehyde level in thigh muscle at d 42 and serum and liver at d 24 and 42. Total saturated fatty acids were depressed (P < 0.05) and total polyunsaturated fatty acid and n-6 were linearly increased (P < 0.05) in serum and thigh by the inclusion of phytogenic product compared with the control diet. Supplementation with thymol + carvacrol also increased intestinal and pancreatic trypsin, lipase, and protease activities in 24-d-old (linear, P < 0.05) but not in 42-d-old birds. Thymol + carvacrol modified (linear, P < 0.05) immune response by increasing hypersensitivity response, total and IgG anti-sheep red blood cell titers, and decreasing heterophil to lymphocyte ratio compared with the control group. However, hematological parameters and lymphoid organ weight were not affected by thymol + carvacrol. Thus, feed supplementation with thymol + carvacrol enhanced performance, increased antioxidant enzyme activities, retarded lipid oxidation, enhanced digestive enzyme activities, and improved immune response of broilers.

A study was conducted to investigate the effects of supplementation of dried tomato pomace (DTP) on growth performance, relative weights of viscera, serum biological parameters, antioxidant status, immune response, and bone composition of broilers exposed to a high ambient temperature. A total of 352 one-day-old male broiler chickens were randomly divided into four groups consisting of four replicates with 22 birds each. One group was reared under the thermoneutral zone and fed a corn-soybean meal basal diet. The other three groups were subjected to a cyclic heat stress from 29 to 42 days of age (34 ± 1 °C, 55 % RH, 5 h/day). These birds were fed corn-soybean meal basal diet or the same diet supplemented with 3 % DTP (420 mg lycopene/kg diet) or 5 % (708 mg lycopene/kg diet) of DTP. Blood samples were collected on days 28 and 42, and the birds were slaughtered at the same times. Supplementation of 5 % of DTP increased body weight and production index and decreased feed conversion ratio during 1-28 days of age. On day 28, the broilers supplemented with 5 % DTP had lower serum triglycerides and higher high-density lipoprotein (HDL) cholesterol concentration than those on the other dietary treatments. The activities of glutathione peroxidase (GPx) and superoxide dismutase (SOD) were higher and the concentration of malondialdehyde (MDA) was lower in the broilers fed 5 % TP than those of the broilers fed other diets at 28 days of age. The effects of heat stress (HS) were impaired body weight, enhanced serum activities of alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, lipase, and MDA concentration while reducing the activities of GPx and SOD. Dried tomato pomace supplementation did not influence growth performance under HS but ameliorated the negative effects of HS on the serum enzyme activities, GPx activity, and lipid peroxidation. Heat stress did not change the relative weights of the lymphoid organs but reduced the total and IgG titers for secondary antibody response to sheep red blood cells and titer against Newcastle disease virus and increased the heterophil/lymphocyte ratio. The supplementation with 5 % of DTP completely alleviated the negative effects of HS on immune responses. The ash, Ca, and P contents of the tibia bone were decreased under HS. The ash and Ca contents of the tibia were not significantly different between thermoneutral and heat-stressed broilers supplemented with 5 % DTP. In conclusion, dietary supplementation of DTP, particularly 5 % DTP, to broiler diet attenuated the detrimental effects of HS on the activities of serum enzymes, oxidative status, immune response, and bone composition.

In this experiment, the effect of hydroalcoholic grape seed extract (GSE) and vitamin C feed supplementation on some blood parameters and heat shock protein 70 (<em>HSP70</em> gene) expression of broiler chickens suffering from chronic heat stress was investigated. Experimental diets included control diet (with no additive), 3 levels of GSE (150, 300, 450 mg/kg), and one level of vitamin C (300 mg/kg). Each diet was fed to 5 replicates of 12 male chicks each, from d 1 to 42. The birds suffered from chronic daily heat stress under 34±1°C temperature with 65 to 70% relative humidity for 5 h from 29 to 42 d of age. Results showed that 300 mg/kg GSE supplementation increased body weight of broilers both before and after heat stress condition (at 28 and 42 d, respectively). Also, birds fed 300 mg GSE/kg diet had higher European production efficiency factor during the whole period of the experiment. Supplementation of GSE decreased the concentration of serum glucose at 28 and 42 d; at 42 d (during heat stress condition) and at 450 mg/kg diet it decreased cholesterol, triglyceride, lowand very low density lipoprotein concentration of serum blood. Vitamin C supplementation decreased serum cholesterol concentration of broilers suffering from heat stress. <em>HSP70</em> gene expression in heart and liver of broilers reduced by GSE and vitamin C supplementation pre- and during chronic heat stress condition.

This study investigated the effect of dietary α-tocopherol (α-Toc), pomegranate peel extract (PPE), and pomegranate peel (PP) on phenolic content and breast meat quality of broilers during 11 days of storage with the addition of α-Toc, PPE, and PP. Broilers were fed eight dietary treatments, including: control diet, α-Toc diet (200 mg/kg), PPE diets (100, 200, and 300 mg/kg), and PP diets (1, 2, and 3 g/ kg) during 0-42 days. The extents of lipid oxidation in samples were assessed by measuring thiobarbituric acid-reactive substances and the 1, 1-Diphenyl-2-picrylhydrazyl radical-scavenging activities were determined. The feed efficiency was improved significantly in chickens fed diet containing 0.2 g/kg PPE, and the growth performance of chickens was impaired in chickens fed with PP diet. Long-chain polyunsaturated fatty acids n-3 were increased in breast muscles of broilers fed α-Toc and high levels of PPE diets (P < .05). Total phenolic contents and antioxidant activity in the breast meat were improved significantly when chickens fed diets containing α-Toc and PPE (P < .05). In conclusion, dietary supplementation with 200 and 300 mg/kg PPE may improve the antioxidant potential and quality indices of broilers breast meat. The antioxidant potential of PPE was equal to that of α-Toc in refrigerated meat.

The effects of supplementation with a-tocopherol acetate (a-Toc), pomegranate pomace extract (PPE) and pomegranate pomace (PP) into chicken feed on antioxidant status, oxidation susceptibility and quality of the thigh meat during refrigeration were investigated. During six weeks broiler chickens were fed eight dietary treatments, which included: control diet, a-tocopherol diet (200 mg kg À1), PPE diets (0.1, 0.2 and 0.3 g kg À1) and PP diets (1, 2 and 3 g kg À1). Feed efficiency was significantly improved by supplementing chickens fed diet with 0.2 g kg À1 PPE. Long chain polyunsaturated fatty acids (LC PUFA) n-3 level was higher in the thigh of broilers fed with a-Toc and PPE diets (except 0.1 g kg À1) than in chickens fed control and PP diets (p < .05). Total phenolic content, lipid peroxidation level and 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity in the thigh meat were significantly improved when chickens were fed diets containing a-Toc and PPE (p < .05). Supplementation of different antioxidant preparations into diets had no influence on plasma superoxide dismutase and glutathione peroxidase activities, in contrast, serum lipid peroxidation level was reduced in chickens fed diets supplemented with PPE (except 0.1 g kg À1) and a-Toc. In conclusion, the broiler thigh meat may be successfully enriched with LC PUFA n-3 and its antioxidant potential and quality characteristics may be improved by supplementing diets with 0.2 and 0.3 g kg À1 PPE. Moreover, the antioxidant potential of PPE supplementation was equal to that of a-tocopherol acetate in refrigerated meat.

In making general recommendations for amino acids, researchers might survey various published data on the responses of poultry to amino acids. In this way, the use of appropriate mathematical and statistical approaches may help researchers draw appropriate conclusions. The purpose of this study was to develop artificial neural network (ANN)-based models to analyze data on the responses of broiler chickens [ADG and feed conversion ratio (FCR)] to protein and threonine from 21 to 42 d of age. A data set containing 92 dose-response treatments was extracted from the literature, compiled, and entered into the training and testing sets of the ANN models. The constructed models were subjected to a process of sensitivity analysis to evaluate the relative importance of the effects of dietary protein and threonine on ADG and FCR. Optimal values for the input variables (protein and threonine requirements) to maximize ADG and minimize FCR in birds were obtained by using the ANN models with an optimization algorithm. Based on the calculated goodness of fit criteria, it appeared that the platform of ANN-based models with the sensitivity analysis and optimization algorithms was an efficient tool for integrating published data on the responses of broiler chickens to threonine. The analyses of ANN models for ADG and FCR based on the compiled data set suggested that the dietary protein concentration was more important than the threonine concentration. The optimization algorithm revealed that diets containing 18.69% protein and 0.73% threonine could lead to optimal ADG, whereas the optimal FCR could be achieved with diets containing 18.71% protein and 0.75% threonine.

The effects of three plant extracts, i.e. lemon peel extract (LPE), orange peel extract (OPE) and Curcuma xanthorrhiza essential oil (CXEO), on the performance and gut health parameters of broilers exposed to high temperature was investigated. A total of 336 unsexed Ross 308 broilers were distributed to seven dietary treatments, a control diet and six diets containing 200 or 400 mg kg-1 feed of one of the three products between d 25-38 (12 chicks per pen, four replicates). To induce chronic heat stress, the temperature was increased to 34°C with 50% relative humidity for 5 h daily starting from d 28 until d 38. At d 38, four animals per pen were sampled for morphological characteristics (duodenum, jejunum and ileum) and microbial counts (ileo-cecal contents). Plant extracts did not affect the bird performance. The bursa weight of the control birds was lower (p<0.05) comparing to those fed 400 mg kg-1 OPE and 200 and 400 mg kg-1 CXEO diets. Feeding 400 mg kg-1 of LPE decreased the duodenal villus:crypt ratio compared to control and 200 mg kg-1 OPE fed birds. Plant extracts did not have effect on ileal histo-morphology. Feeding with 400 mg kg-1 of LPE and CXEO caused a decrease in coliform counts in ileum and feeding of 400 mg kg-1 CXEO diet decreased coliform counts in caecum compared to control birds (p<0.05). These results elucidate that CXEO, OPE and LPE might modify some microbial and intestinal traits, but without beneficial effect on performance of broilers under heat stress.