Introduction

Heat stress is a major environmental stressor that may have deleterious effects on growth performance, nutrient availability, immunity, and welfare of broiler chickens (Sahin et al. 2008; Lara and Rostagno 2013). High ambient temperatures could increase the production of reactive oxygen substances (ROS), which may cause damage to critical biomolecules including lipids, proteins, and DNA, resulting in reduced welfare, performance, meat quality, increased tissue damage, and bone loss (Rao et al. 2003; Sahin et al. 2008; Abidin and Khatoon 2013).

Several nutritional approaches such as supplementation of diets with antioxidant vitamins and minerals and phytochemicals have been used attempted to attenuate the negative effects of heat stress (Sahin et al. 2008; Selim et al. 2013; Habibian et al. 2014; Perai et al. 2015). Tomato pomace, a by-product of tomato processing, contains antioxidant compounds including lycopene, folate, vitamin C, β-carotene, α-tocopherol, phenolics, and flavonoids (Sahin et al. 2008; Selim et al. 2013). Lycopene is a strong antioxidant among dietary carotenoids and can prevent the production of ROS and associated undesirable effects (Palozza et al. 2011). An inverse relationship between lycopene, tomato, or tomato products intake and the levels of oxidative stress biomarkers was reported by Palozza et al. (2011) and Sahin et al. (2011). Sahin et al. (2008) reported that tomato powder supplementation linearly increased feed intake, weight gain, feed efficiency, serum concentrations of lycopene, and vitamins A, C, and E and decreased the malondialdehyde levels in the serum, liver, and muscles of Japanese quails under heat stress. Similar effects of lycopene on the performance and antioxidant status of Japanese quails exposed to chronic heat stress have been reported (Sahin et al. 2006a, b). In a more recent study, supplementation of tomato puree at the rate of 0.5 % improved feed intake, weight gain, and feed conversion and at the level of 1 % also increased the total antioxidant capacity and reduced malondialdehyde (MDA) concentration in heat-stressed broilers (Selim et al. 2013). It has been shown that incorporation of dried tomato pulp in diet at a level of 5 % exerted antioxidant properties on quail breast meat, whereas supplementation at a level of 10 % showed a prooxidant effect (Botsoglou et al. 2004). There is evidence suggesting a depression in the relative weight of the lymphoid organs and antibody production during heat stress conditions (Lara and Rostagno 2013; Habibian et al. 2014). Although limited data are available on the effect of tomato derivatives on the immune response of heat-stressed birds, Selim et al. (2013) reported that supplementing tomato puree enhanced titers against Newcastle disease virus (NDV) and infectious bronchitis virus in broilers reared under heat stress conditions. However, Olson et al. (2008) did not report any positive effect of lycopene supplementation on the immune response (inflammatory, cutaneous basophil hypersensitivity, 1° and 2° antibody response) of laying hens. To the best of our knowledge, little information is available regarding the effects of supplementation of tomato by-products as a dietary management strategy for ameliorating the negative effects of heat stress in broilers. The objective of the present study was to elucidate the effects of dried tomato pomace on performance, serum biochemical parameters, immune response, antioxidant status, and bone composition of broilers kept under a high environmental temperature.

Materials and methods

Birds, diets, and experimental design

A total of 352 one-day-old male Arian broiler chicks were randomly assigned to four groups with four replicates of 22 birds in each from 1 day of age. The major antioxidant component of tomato pomace (TP) is lycopene. The lycopene content of TP was 145 mg/kg. Two groups received corn–soybean meal basal diets (control groups). The remaining two groups were fed either on the basal diets containing 3 % (420 mg lycopene/kg diet) dried tomato pomace (DTP) or the basal diets containing 5 % (708 mg lycopene/kg diet) DTP. The birds were fed a mash starter diet until 21 days of age and a mash grower diet from 22 to 42 days of age (Table 1). Feed and water were provided ad libitum. A lightening schedule of 22 h of light followed by 2 h of darkness was maintained during the experiment. The initial room temperature was set at approximately 32 °C and, thereafter, was gradually reduced based on normal management practice to 21 °C by 28 days of age. At 29 days of age, one of the control groups was kept in an environment-controlled room at 21 °C with a relative humidity of 55 % (thermoneutral, TN group), whereas the other three groups were kept in another heat-controlled room or heat stress room. The birds were exposed to 15 h of 21 °C,, 2 h of 21 to 34 °C, 5 h of 34 ± 1 °C, and 2 h of 34 to 21 °C (Fig. 1). The relative humidity of 55 % for 5 h/day were also applied in heat stress (HS) (10.30 am–15.30 pm; heat stress, HS groups). All animal research procedures were assessed and approved by the Animal Care Committee of Ferdowsi University of Mashhad.

Table 1 Ingredients (%) and nutritive values of the experimental diets
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Fig. 1
figure 1

Heat stress patterns used in the broilers in the experiment (29–42 days). A constant of 21 °C was applied for the thermoneutral (TN) room, whereas a daily heat stress (21–34 °C) was applied for the heat-stressed room

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Growth performance measurements

Feed intake (FI) and body weight were recorded each week for each replicate (pen) and also were recorded at 28 and 42 days of age after fasting for 5 h. The European broiler index (EBI; 100*[(body weight*livability)/(FCR* rearing period (day))]) and feed conversion ratio (FCR; gram feed intake to gram weight gain) were then calculated (Marco et al. 2013).

Carcass characteristics measurements

For carcass evaluation, at 28 and 42 days of age, two birds from each replicate with a body weight close to the group average were randomly chosen and weighed individually after a 5-h fasting. The broilers were killed by cervical dislocation, and the abdominal fat, the bursa of Fabricius, and the spleen were harvested and weighed individually. The organ weights were expressed as a percentage of live body weight.

Bone characteristics

To study bone composition at 42 days of age, the right tibia of the slaughtered birds (eight birds/treatment) were collected and the soft tissues were removed. The bone and claw were then dried in a drying oven at 80–120 °C for 24 h. The bone was weighed to the nearest 0.1 mg and ashed in a muffle furnace at 550 °C for 12 h, and the ash weight was determined to the nearest 0.1 mg. The calcium and phosphorus contents of the tibia were measured using an atomic absorption spectrophotometer (Thermo Model 97 GFS). These parameters were expressed as a percentage of the dry weight of the tibia.

Serum metabolites

At 28 and 42 days of age, blood was sampled from eight birds (two/replicate) randomly selected from each treatment by left wing venipuncture after a 5-h feed deprivation and collected in heparinized and non-heparinized tubes. The blood samples were centrifuged at 3000×g for 10 min to obtain serum, which were kept at −20 °C in Eppendorf test tubes until analysis. The buffy coat was carefully removed, and then, the sedimented cells were washed three times by resuspending in isotonic phosphate-buffered saline, followed by recentrifugation and removal of the supernatant fluid and buffy coats. The washed erythrocytes were then lysed with ten volumes of ice-cold distilled water to prepare erythrocyte hemolysates. The hemolysates were stored at −70 °C for later analysis (Perai et al. 2015).

The serum concentrations of triglyceride, cholesterol, and enzyme activities of alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), creatine kinase (CK), lactate dehydrogenase (LDH), and lipase were measured using BioSystems kits and associated procedures (BioSystems S.A. Costa Brava 30, 08030 Barcelona, Spain). Serum high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) concentrations were determined using Pars Azmoon kits (Pars Azmoon Co; Tehran, Iran).

Antioxidant parameters

Lipid peroxidation in plasma was determined as thiobarbituric acid-reactive substances (TBARS) by the method described by Yoshioka et al. (1979). Briefly, 1.0 mL of 0.67 % TBA and 2.5 mL of 20 % trichloroacetic acid (TCA) were added to a 0.5-mL plasma sample and heated in a boiling water bath (100 °C) for 30 min. After cooling of the mixture in a water bath (2 °C) for 10 min, 4 mL of n-butanol was added. The mixtures was then mixed and vortexed for 2 min and then centrifuged at 3000 rpm for 10 min. Following that, the upper n-butanol layer was separated and the absorbance was read at 535 nm. The serial dilution curves were plotted based on a series of standard solutions (1,1,3,3-tetramethoxypropane), and after that, the sample values were compared to the standard curve. Results were expressed as nmol/mL. The erythrocyte activity of glutathione peroxidase (GPx) and superoxide dismutase (SOD) were measured in erythrocyte hemolysates using assay kits (Ransel and Ransod test kits, Randox Laboratories Ltd, UK).

Immune system

In the present experiment, two strategies were applied to assess the effects of treatments on humoral immune response: (i) live Newcastle disease vaccine (LaSota strain) was administrated via drinking water at 8, 18, and 28 days of age and (ii) the sheep red blood cells (SRBCs) were injected into the vein of the broilers at 22 and 35 days of age. The sera were collected, and the antibody titers against SRBCs (Nelson et al. 1995) and NDV (using hemagglutination inhibition test) were measured at 28 and 42 days of age. On 40 days of age, 1.0 mL of whole blood was collected in heparinized capillary tubes, blood smear was prepared using May–Grunwald–Geimsa stain, and then heterophil and lymphocytes were counted to a total number of 100 cells/slide (Gross and Siegel 1983).

Statistical analysis

For assessing the normality, data were assessed using Shapiro–Wilk test, stem and leaf plots, and normal probability plots using SPSS statistical software. The data including thermoneutral (TN) and three other groups were analyzed as a completely randomized design using the GLM procedure of SAS (SAS Institute 2003).

The model was used as Y ij = μ + T j + e ij.

  • μ, overall mean

  • T j, treatment effect

  • e ij, experimental error

Differences among the treatment means were detected using Tukey’s test. Statements of significance were based on P ≤ 0.05.

Results

Growth performance

Feed intake was not affected by DTP supplementation at 28 days of age. Supplementation of 5 % DTP significantly improved body weight, feed conversion ratio (FCR), and European broiler index (EBI) during this period (P < 0.05). Heat stress significantly decreased body weight (P < 0.05) but did not affect FI, FCR, and EBI. The broilers supplemented with 5 % DTP had higher body weight than the broilers fed 0 or 3 % of DTP during HS (Table 2).

Table 2 Body mass, feed intake, feed conversion ratio, and production index of broilers reared under thermoneutral or cyclic heat stress conditions
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Blood parameters

Dried tomato pomace supplementation did not change serum concentrations of cholesterol and LDL cholesterol in thermoneutral conditions (Table 3). However, supplementation of 5 % DTP reduced serum concentrations of triglyceride and increased concentration of HDL cholesterol before HS (P < 0.05). Heat stress did not influence serum lipid profile. Dried tomato pomace did not affect concentrations of triglyceride, cholesterol, and LDL cholesterol during the heat stress period. HDL-cholesterol concentration of the broilers fed 5 % DTP was significantly higher compared to that of the broilers fed control diet during HS (P < 0.05).

Table 3 Serum lipid profile of a broiler reared under thermoneutral or cyclic heat stress conditions
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Heat stress did not affect serum activities of CK and LDH and significantly increased serum activities of ALP, ALT, AST, and lipase. Supplementation of 5 % DTP reduced ALP and lipase activities during HS (P < 0.05; Table 4).

Table 4 Serum enzyme activities of a broiler reared under thermoneutral or cyclic heat stress conditions at 42 days of age
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Antioxidant parameters

Before HS, the activities of GPx and SOD were significantly higher in the broilers fed high level of DTP than those of broilers fed control diet (P < 0.05). Supplementation of 5 % DTP significantly reduced the concentration of MDA during this period. Heat stress significantly decreased GPx and SOD activities and increased MDA concentration. Dried tomato pomace significantly increased the activity of GPx and reduced the concentration of MDA during heat stress conditions (P < 0.05; Table 5).

Table 5 Antioxidant status of a broiler reared under thermoneutral or cyclic heat stress conditions
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Humoral immune response and heterophil/lymphocyte ratio

Titers of total, IgM, and IgG antibodies for primary response to SRBCs, antibody production against NDV, and the ratio of heterophil/lymphocyte (H/L) were not significantly different among dietary treatments at 28 days of age. Heat stress decreased titers of total and IgG antibodies for secondary response to SRBCs and antibody production against NDV and increased the ratio of H/L (P < 0.05). Supplementation of 5 % DTP increased titer of the total antibody for secondary response to SRBCs and antibody production against NDV and decreased the ratio of H/L during HS (P < 0.05), whereas the titers of IgM and IgG antibodies for secondary response to SRBCs were not significantly affected by dietary treatments (Table 6).

Table 6 Immune response of a broiler reared under thermoneutral or cyclic heat stress conditions
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Organ weights and bone composition

Dried tomato pomace reduced the relative weight of the abdominal fat and did not affect the relative weight of the spleen before HS. The treatment with 5 % DTP significantly increased the relative weight of the bursa of Fabricius before HS (P < 0.05). The relative weights of the abdominal fat, spleen, and bursa of Fabricius were not influenced by HS conditions. The DTP supplementation reduced the relative weight of the abdominal fat in heat-stressed broilers (P < 0.05; Table 7).

Table 7 Relative weights of the bursa of Fabricius, spleen, and abdominal fat and bone chemical composition of a broiler reared under thermoneutral or cyclic heat stress
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Heat stress significantly decreased the ash, Ca, and P contents of the tibia bone as compared to the tibia of the broilers in the thermoneutral condition (P < 0.05). The ash, Ca, and P contents of the tibia were not significantly different among TP dietary treatments subjected to HS (Table 7).

Discussion

The results of this study indicated that the supplementation of 5 % of DTP to broiler diets improved body weight and EBI from 1 to 28 days of age. Exposure of broilers to heat stress reduced body weight without affecting the FI, FCR, and EBI. Supplementation, especially supplementation with the 5 % of DTP, slightly improved the body weight and FCR of broilers under heat stress. Similar to the result of the present study, Geraert et al. (1996) reported that exposure to heat stress decreased a broiler’s body weight by 14 and 24 % during 15–28 and 29–42 days of age, respectively. Moreover, Habibian et al. (2014) found that broilers exposed to chronic heat stress had significantly reduced FI and body weight at 49 days of age. The impaired growth performance of broilers subjected to high ambient temperatures may be associated with decreased FI, impaired digestion and metabolism, the genetic makeup of birds, and reduced size and secretion of the thyroid gland (Abidin and Khatoon 2013). In a previous study, Sahin et al. (2008) investigated the effects of tomato powder supplementation (2.5 and 5 %) on performance and lipid peroxidation in quails under thermoneutral and heat stress conditions. The obtained results revealed that supplementation with tomato powder only enhanced performance parameters of heat-stressed broilers. In addition, Selim et al. (2013) observed significant improvements in FI, body weight gain, and FCR of heat-stressed broilers supplemented with 0.5 % tomato puree.

Serum activity of AST is commonly used as an indicator of damage to the liver and to the skeletal and cardiac muscles (Hoffmann and Solter 2008). The serum activity of this enzyme was increased significantly by heat stress in the present study. Serum ALT, as a screening test for hepatocellular injury (Hoffmann and Solter 2008), was also increased due to heat stress conditions. The increased activities of AST and ALT suggest that the heat-stressed broilers may have experienced liver damages, which may be associated with induced lipid peroxidation (Abidin and Khatoon 2013). These results are inconsistent with those of Sohail et al. (2011) and Imik et al. (2013), who reported that the activities of AST and ALT in broilers were unaffected by chronic heat exposure. The results of the present study also indicated that heat stress had no significant effects on the serum activities of CK and LDH. In contrast, Gursu et al. (2004) reported declines in the activities of CK and LDH in broilers reared under HS. In the present study, dietary DTP supplementation did not significantly change the serum activities of ALT, AST, CK, and LDH. However, the activities of these enzymes were numerically decreased in the heat-stressed broilers supplemented with DTP. In this experiment, ALP and lipase activities were higher in the heat-stressed broilers without any supplement compared with the non-stressed broilers. The ALP is a Zn metalloenzyme and is active in many tissues and cells including the liver, bone, kidney, muscle, and intestinal mucosa. The results of the present study revealed that HS increased the serum activities of ALP and lipase, which may be related to hepatic and renal diseases and increased glucocorticoids secretion (Hoffmann and Solter 2008). Supplementation of DTP alleviated the effects of heat stress on the serum ALP and lipase activities. However, only supplementation of 5 % DTP reduced the activities of theses enzymes to the levels found in the non-stressed broilers.

In this study, the broilers supplemented with 5 % of DTP had lower triglyceride and higher HDL cholesterol concentrations as compared to the other broilers before HS. The serum concentrations of triglyceride, cholesterol, LDL cholesterol, and HDL cholesterol were unaffected by HS in this study, which are in line with the results of Imik et al. (2013) who reported that HS did not change the levels of triglyceride, cholesterol, LDL cholesterol, and HDL cholesterol in broilers. On the other hand, Gursu et al. (2004) found increased concentrations of triglyceride, cholesterol, and HDL cholesterol in heat-stressed broilers. Supplementing the DTP in the diet did not influence the serum levels of triglyceride, cholesterol, and LDL cholesterol under heat stress conditions. The broilers receiving the diet containing 5 % of DTP had significantly higher concentration of HDL cholesterol than those receiving the other diets during heat stress period. These results are partly consistent with the results of Selim et al. (2013) who reported that supplementation of tomato puree to heat-stressed broilers had no significant effects on the concentrations of total lipids, triglyceride, cholesterol, LDL cholesterol, and HDL cholesterol. Several studies reported hypocholesterolemic effects of tomato derivatives and lycopene in animals and humans. Supplementation with tomato juice for a 4-week period decreased serum total lipids, total cholesterol, and LDL cholesterol and increased HDL cholesterol in rats (Hassan and Edrees 2004). Either alone or in combination, supplementation with lycopene and vitamin E reduced serum and yolk cholesterol, and the greatest response was observed with the combination of them (Sahin et al. 2006a, b). The hypocholesterolemic properties of tomato products and lycopene may be related to a decrease in cholesterol synthesis through the inhibition of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity and expression, modulation of LDL receptor, and inhibition of the activity of acyl-coenzyme A:cholesterol acyltransferase (ACAT) (Palozza et al. 2012).

The results of the present study demonstrated that the supplementation of 5 % of DTP caused increased hemolysate activities of GPx and SOD as well as a decreased level of MDA in the plasma of the broilers reared under a thermoneutral temperature. Exposure to chronic heat stress significantly reduced the activities of GPx and SOD and increased the concentration of MDA in the broilers. The present study also suggests that supplementation of different levels of DTP completely and partially alleviated the detrimental effect of HS on the GPx activity and lipid peroxidation, respectively. Similar to the results of the present study, the activities of antioxidant enzymes such as GPx and SOD were decreased and the concentration of MDA was increased when quails were subjected to a high temperature (Sahin et al. 2011). However, Aengwanich and Suttajit (2013) found that when broilers were subjected to heat stress on day 1 of the experimental period, the activity of GPx was increased, but when broilers had adapted to heat stress conditions, the GPx activity was not significantly different between the thermoneutral and heat-stressed broilers. Tomato derivatives have significant amounts of antioxidant compounds including lycopene, vitamins C, E, and A, β-carotene, lutein, and zeaxanthin (Sahin et al. 2008). Tomato product consumption not only can influence the status of these microconstituents in body tissues but also may maintain the levels of the antioxidant vitamins through its antioxidant property (Sahin et al. 2008). Lycopene is the main carotenoid in tomato that it is able to scavenge hazardous free radicals (nitrogen dioxide, hydrogen peroxide, sulphonyl radicals) and also is able to inhibit the ROS production (Palozza et al. 2011). Increasing evidence suggests that tomato products and lycopene can protect the vital biomolecules including lipids, proteins, and DNA from the detrimental effects of ROS and then decrease the risk of cancer and other diseases (Palozza et al. 2011). It has been reported that lycopene can upregulate the antioxidant electrophile/antioxidant response element (EpRE/ARE) and thereby induce the production of cellular enzymes, such as superoxide dismutase, glutathione S-transferase, and quinone reductase that protect cells from ROS and other electrophilic molecules (Sahin et al. 2014). Malondialdehyde is the end product of lipid peroxidation, and therefore, it is used as a marker of lipid damage by ROS (Perai et al. 2015). In a previous study, Sahin et al. (2004) have shown that serum oxidative stress markers such as homocysteine and MDA were decreased and the concentrations of vitamins C, E, and A and lycopene were increased by pure lycopene supplementation to heat-stressed quails. Sahin et al. (2008) also reported that dietary supplementation with tomato powder decreased the concentration of MDA in the serum, breast, leg, and liver while causing increases in the levels of serum lycopene, vitamin C, vitamin E, and vitamin A in quails under thermoneutral and high temperatures. Supplementation of broiler diet with 2.5 and 5 % tomato powder decreased liver MDA concentration while increased liver concentrations of lycopene, SOD, GPx and catalase in quails reared under heat stress conditions (Sahin et al. 2011). A recent study found that inclusion of tomato puree (1 %) in broilers diets resulted in an increase in plasma total antioxidant capacity and a decrease in MDA concentration of heat-stressed broilers (Selim et al. 2013).

At 28 days of age, the relative weight of the spleen was similar among dietary treatments, while the relative weight of bursa of Fabricius higher in the 5 % DTP-fed broilers than the broilers fed control diet. The results of the present study also indicated that the titers of total, IgM, and IgG for primary response to SRBCs, titer against NDV, and the ratio of H/L were not affected by dietary treatments at 28 days of age. Exposure of the broilers to heat stress did not significantly affect the relative weights of the lymphoid organs but resulted in significant decreases in the titers of total and IgG for secondary response to SRBCs and titer against NDV and a significant increase in the ratio of H/L. Increasing evidence shows an immunosuppressing effect of high ambient temperatures in the birds. Reduced relative weights of lymphoid organs (Habibian et al. 2014; Lara and Rostagno 2013) and fewer lymphocytes in the cortex and medulla areas of the bursa (Lara and Rostagno 2013) have been reported under heat stress. Similar to the results of the present study, Bartlett and Smith (2003) and Habibian et al. (2014) reported that primary and secondary responses to SRBCs were decreased in broilers subjected to heat stress. In the present study, inclusion of DTP at level of 5 % increased the titer of total antibody in response to SRBCs and titer against NDV and decreased the ratio of H/L in heat-stressed broilers. These results are in accordance with the findings of Selim et al. (2013), who demonstrated that supplementation of tomato puree significantly increased the values of blood titers against NDV and infectious bronchitis virus and decreased the ratio of H/L in broilers reared under summer conditions. In contrast, Olson et al. (2008) reported that the dietary lycopene supplementation (420 and 840 mg/kg) for 15 days had no significant effects on immune responses (inflammatory, cutaneous basophil hypersensitivity, 1° and 2° antibody response) of laying hens. Recently, Sun et al. (2014) reported that the indices of the thymus and bursa of Fabricius were decreased in lipopolysaccharide-stimulated broilers, and lycopene increased the indices of the thymus, bursa of Fabricius, and spleen. Through modulating surface molecules for primary immune response, ROS production, carotenoid localization in or within cell membrane, and the activity of mitogen-activated protein kinase and transcription factors such as nuclear factor-kB, lycopene may affect the levels of cytokine and therefore can influence the immune responses and inflammation (Palozza et al. 2011).

Bone problems are a potential health issue in meat-type poultry. Heat stress can reduce the skeletal strength, which is related to leg problems, bone deformities, breakage, infections, and osteoporosis, resulting in poor performance and welfare. Glucocorticoids especially corticosterone secretion may be increased in chicks under heat stress conditions (Lara and Rostagno 2013), which can influence calcium and bone metabolism and results in bone loss. Glucocorticoids may decrease maturation and increase apoptosis of osteoblasts, resulting in a reduction of bone formation (Silverman and Lane 2009). In addition, glucocorticoids may increase osteoclast maturation and activity, further contributing to increased bone resorption (Silverman and Lane 2009). Increased mineral excretion was seen in birds maintained under high environmental temperatures. It has been reported that the retention rates of P, K, Na, Mg, S, Mn, Cu, and Zn reduced when temperature goes above the thermoneutral zone (Belay and Teeter 1996). In the present study, heat exposure significantly reduced the contents of ash, Ca, and P in the tibia. Similarly, Sahin et al. (2006a, b) reported that the tibia contents of ash, Ca, P, Mg, and Mn decreased significantly in quails reared under HS. In addition, Onderci et al. (2006) showed that the excretions of Ca and P were increased, and the concentrations of these elements in the tibia were reduced at an ambient temperature of 34 °C when compared to 22 °C. In this experiment, the ash and Ca contents of the tibia bone were not significantly different between the thermoneutral and the 5 % DTP-fed broilers. To our knowledge, this is the first study to investigate the effect of tomato derivatives on bone characteristics in heat-stressed birds. As mentioned, tomato pomace contains several antioxidant compounds including vitamins C and E and lycopene. Previous evidences suggest that certain antioxidants such as vitamin C, vitamin E, and lycopene can reduce the risk of osteoporosis (Rao et al. 2003). Vitamin C is essential for the formation of collagen and fracture healing and can affect bone density in poultry. Lohakare et al. (2005) showed that dietary supplementation with vitamin C significantly increased the bone-breaking strength and the contents of crude ash, Ca, and P of the tibia bone of broilers subjected to heat stress. Wattanapenpaiboon et al. (2003) reported a positive relationship between lycopene intake and mineral content and mineral density of the bone. Increasing evidences suggest that oxidative stress can affect bone development. In a human study, an association between enhanced oxidative stress marker 8-isoprostaglandin F2a and diminished bone density was demonstrated (Basu et al. 2001). In a previous experiment, Rao et al. (2003) found that lycopene supplementation prevented formation of tartrate-resistant acid phosphatase multinucleated osteoclasts, osteoclastic resorption, and ROS production in osteoclasts. Recently, supplementation with lycopene significantly increased serum total antioxidant capacity and decreased lipid peroxidation, protein oxidation, and bone resorption marker N-telopeptide (Mackinnon et al. 2011).

Conclusion

Supplementation with 5 % of DTP improved growth performance, decreased triglycerides, and increased HDL cholesterol concentration of teh broilers reared under thermoneutral temperature. Moreover, GPx and SOD activities were increased, and MDA concentration was decreased with 5 % DTP. Exposure to heat stress impaired body weight, increased serum activities of ALT, AST, ALP, and lipase and MDA concentration while reducing the activities of GPx and SOD and ash, Ca, and P contents of the tibia bone. Dietary supplementation of DTP, particularly 5 % DTP, partly or completely restored the heat stress-induced impairments in serum enzyme activities, antioxidant status, immune response, and bone composition.