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Influence of Vitamin E Supplementation and Stocking Density on Performance, Thyroid Status, Some Blood Parameters, Immunity and Antioxidant Status in Broiler Chickens



F.S.A. Ismail, M.R. El-Gogary and M.I. El-Nadi
 
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ABSTRACT

The present study was carried out to investigate the effects of dietary supplementation with vitamin E and stocking density on performance, thyroid function, plasma concentration of corticosterone (Cort), some blood parameters, (antibody (Ab) titers against Newcastle Disease Virus (NDV) and Avian Flu virus (AF)) and antioxidant status in broiler chickens. In all 192; 3-day-old commercial broiler chickens (cobb 500) were randomly divided into 8 treatments groups, each of which include 4 replicates. Experimental treatments consisted of a 4x2 factorial arrangement design with 4 levels of vitamin E and 2 levels of stocking density (11.90 birds m-2 as the normal stocking density or 16.66 birds m-2 as the high stocking density). Vitamin E levels were 0.0, 200, 300 and 400 mg kg-1 diet. Increasing vitamin E level in the diet did not affect Live Body Weight (LBW), Body Weight Gain (BWG), feed intake and FCR. Also, increasing vitamin E levels had no effects on T4, Total Lipids (TL), total cholesterol (Chol) and high density lipoprotein cholesterol (HDL). However, supplementing vitamin E had a significant effect on SOD, NDV and AF titers but decreasing effect on MDA. In addition, plasma Cort and LDL levels were lower at 300 mg kg-1 vitamin E supplementation but plasma Total Protein (TP) and albumin (Alb) levels were higher at 300 mg kg-1 vitamin E supplementation. The normal stocking density has significant effects on LBW, BWG, FI, Cort, TP, TL and chol compared with the high stocking density. However, stocking density did not affect FCR, T3, T4, Alb, LDL, HDL and SOD. The results of the present study show that supplementing of vitamin E at 300 mg kg-1 of diet has a positive effect on productivity, immunity and blood parameters in broiler chickens.

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F.S.A. Ismail, M.R. El-Gogary and M.I. El-Nadi, 2014. Influence of Vitamin E Supplementation and Stocking Density on Performance, Thyroid Status, Some Blood Parameters, Immunity and Antioxidant Status in Broiler Chickens. Asian Journal of Animal and Veterinary Advances, 9: 702-712.

DOI: 10.3923/ajava.2014.702.712

URL: https://scialert.net/abstract/?doi=ajava.2014.702.712
 
Received: June 16, 2014; Accepted: September 21, 2014; Published: November 28, 2014



INTRODUCTION

Vitamin E (α-Tocopherol) is an important lipid-soluble antioxidant. It performs its functions as antioxidant in the glutathione peroxidase pathway (Wefers and Sies, 1988) and it protects cell membranes from oxidation by reacting with lipid radicals produced in the peroxidation chain reaction (Herrera and Barbas, 2001; Traber and Atkinson, 2007). This would remove the free radical intermediates and prevent the oxidation reaction from continuing. Supplementation of animal diets with vitamin E increases the content of this natural antioxidant in animal food products and prevents lipid peroxidation in broiler meat (Ajuyah et al., 1993). Tocopherols are mainly found in the hydrocarbon part of membrane lipid bilayer towards the membrane interface and in close proximity to oxidase enzymes which initiate the production of free radicals (Putnam and Comben, 1987; McDowell, 1989; Packer, 1991).

Malondialdehyde (MDA) is one of the most frequently used indicators of lipid peroxidation (a marker of radical induced damage). MDA is a three-carbon low molecular weight aldehyde and spontaneous breakdown product of peroxides that can be produced from free radical attack on poly unsaturated fatty acids (Cordis et al., 1998; Pilz et al., 2000). Superoxide dismutases (SOD) are enzymes that function to catalytically convert superoxide radical to oxygen and hydrogen peroxide. These enzymes carry out catalysis at near diffusion controlled rate constants via a general mechanism that involves the sequential reduction and oxidation of the metal center, with the concomitant oxidation and reduction of superoxide radical (Abreu and Cabelli, 2010). Oxidative stress is known to be an important contributing factor in many chronic diseases (Mahima et al., 2013). The combination of vitamin E is more effective in ensuring adequate stability of the diet and in protecting the bird’s immune system and thereby improving performance (Bou et al., 2004).

Stocking density has major economic implications for the broiler industry as higher profits can be obtained when more animals are housed under one roof.

However, as profits increase, the welfare of the animals may start to decline. Furthermore, the effects of density are multidimensional, because it affects performance, health, welfare of the birds in many different ways (Estevez, 2007). Several morphological anomalies have also been presented, indicating that increased stocking density can compromise immunity (Proudfoot et al., 1979; Greene et al., 1985; McIlroy et al., 1987; Heckert et al., 2002; Thaxton et al., 2006). Therefore, the present study was designed to evaluate supplementation of vitamin E as one of major antioxidants on performance, immunity response, lipid peroxidation and stress indicators of broilers chickens at different stocking densities.

MATERIALS AND METHODS

The experimental work of the present study was carried out in the Poultry Production Farm; Center of Agricultural Research and Experiments, Faculty of Agriculture, Mansoura University, Egypt from May to June.

Birds and management: Cobb 500 broiler chickens (n = 192), 3-day-old, were divided into 8 treatments groups, each of which included 4 replicates (cages). Experiments consisted of a 4x2 factorial arrangement with 4 levels of vitamin E supplementation and 2 stocking densities. Vitamin E (VE) was supplemented to the basal diet at 0, 200, 300, 400 mg kg-1 diet to obtain the dietary VE of 18.84, 218.84, 318.84 and 418.84 mg kg-1 of starter diet, respectively. These levels were 19.15, 219.15, 319.15 and 419.15 mg of VE kg-1 of the grower diet, respectively. Birds were reared in battery cages and the length, width and height of each cage were 70, 60 and 40 cm, respectively. Thus the cage floor area was 0.42 m2 (70x60 cm). The number of birds located in each was 5 or 7 birds per cage density. The stocking density was 11.90 birds m-2 as the normal density (5 birds per cage) and 16.66 birds m-2 as the high density (7 birds per cage). The daily temperature inside the farm in first week was 32°C and then gradually reduced to be ranged from 30-28°C in the 2nd week and maintained at 18-24°C from 3rd week until the end of the experiment. The photoperiod was 23L: The 1 D throughout the experiment. Chickens were reared to 42 days of age and fed a starter ration from three to 17 days of age (3127 kcal of ME kg-1 of diet and 22.51% CP) and grower ration from 18-42 days of age (3.141 kcal of ME kg-1 of diet 19.09% CP). Diets were, formulated to cover or exceed the recommended requirements of broiler chicks according to NRC (1994). Feed in mash form and water (via nipple drinkers) were provided freely. The composition and chemical analysis of the experimental diets are shown in Table 1.

Performance of broiler chickens: Live Body Weight (BW); Feed Intake (FI) and Body Weight Gain (BWG) were measured weekly throughout the experimental period, then Feed Conversion Ratio (FCR) was calculated (feed: Gain g). Mortalities and health status were visually observed and recorded daily throughout the entire experimental period.

Blood sampling and biochemal analysis: Three birds of each treatment were randomly chosen, slaughtered and blood samples were collected in heparinized tubes then centrifuged at 4000 rpm for 15 min and the plasma obtained was stored at -20oC until analysis. Plasma samples were tested calorimetrically using commercial kits according to the procedures outlined by the manufactures, for determination of total protein (Doumas et al., 1981), albumin (Doumas et al., 1971), total lipids (Frings and Dunn, 1970), cholesterol (Allain et al., 1974) high density lipoprotein and low density lipoprotein (Myers et al., 1994). Concentrations of thyroid hormones triiodothyronine (T3) and thyroxine (T4) and corticosterone in blood plasma were measured by RIA techniques according to the methods of Britton et al. (1975) and Satterlee et al. (1980), respectively.

Table 1: Composition and chemical analysis of basal diet fed to the experimental chickens
Image for - Influence of Vitamin E Supplementation and Stocking Density on Performance, 
  Thyroid Status, Some Blood Parameters, Immunity and Antioxidant Status in Broiler 
  Chickens
1Premix provided the following per kilogram of diet: Vitamin A (retinyl acetate), 2654 μg, vitamin D3 (cholecalciferol), 125 μg, vitamin E (dl-α-tocopheryl acetate), 9.9 mg, vitamin K3 (menadionedimethylpyrimidinol), 1.7 mg, vitamin B1 (thiamin mononitrate), 1.6 mg, vitamin B12 (cyanocobalamin), 16.7 μg, riboflavin, 5.3 mg, niacin (niacinamide), 36 mg, calcium pantothenate, 13 mg, folic acid, 0.8 mg, d-biotin, 0.1 mg, choline chloride, 270, BHT, 5.8, Fe (iron sulphate monohydrate), 50 mg, Cu (copper sulphate pentahydrate), 12 mg, I (calcium iodate), 0.9 mg, Zn (zinc oxide), 50 mg, Mn (manganous oxide), 60 mg, Se (sodium selenite), 0.2 mg, Co (cobalt sulphate), 0.2 mg, 2Calculated from data provided by NRC (1994), 3The respective diet formulated to contain 18.84, 218.84, 318.84 and 418.84 mg kg-1 vitamin E and the dose titrations were achieved by addition of vitamin E at the expense of soybean meal

Superoxide dismutase (SOD) was determined by available kit according to Misra and Fridovich (1972) and malondialdehyde (MAD) determined by available kits according to Uchiyama and Mihara (1978). Antibody titers against Newcastle Disease Virus (NDV) and Avian Flu Virus (AF) were determined by hem agglutination inhibition technique using U-Bottonmicrotiter plates (96 wells) as reported by Wegmann and Smithies (1966) and Van der Zijpp et al. (1983). Antigens were prepared manually in incubated chicken eggs, kept frozen as allantois fluid, till used within a month.

Statistical analysis: Statistical analysis for the obtained data was performed by two-way analysis of variance using the method of least square analysis of co-variance (SAS., 1996). Duncan’s multiple range test was used to separate significant differences among means (Duncan, 1955).

RESULTS AND DISCUSSION

Growth performance: The results relating to the influence of vitamin E levels and stocking density on body weight and feed consumption at 42 days of age are shown in Table 2. In present study, increasing vitamin E level in the diet did not affect LBW, BWG, feed intake and FCR (p<0.05). This result is in agreement with Coetzee and Hoffman (2001) who reported that there was no difference (p>0.05) in weight gain or feed conversion ratio between levels of dietary vitamin E supplementation. This observation differs from those of other authors. Hosseini-Mansoub et al. (2010) found that diet enrichment with vitamin E resulted in the better performance of the birds (p<0.05) in comparison with those fed the control diet.

Table 2: Effect of vitamin E levels and stocking density on growth performance of broilers at 42 days of age
Image for - Influence of Vitamin E Supplementation and Stocking Density on Performance, 
  Thyroid Status, Some Blood Parameters, Immunity and Antioxidant Status in Broiler 
  Chickens
a-bMeans in the same colum with different superscripts differ significantly (p≤0.05)

Table 3:Effect of dietary supplementation with vitamin E and stocking density on plasma concentrations of T3, T4 and corticostrone (μg mL-1) in broilers chickens
Image for - Influence of Vitamin E Supplementation and Stocking Density on Performance, 
  Thyroid Status, Some Blood Parameters, Immunity and Antioxidant Status in Broiler 
  Chickens
a-bMeans in the same colum with different superscripts differ significantly (p≤0.05)

The lowest Feed Conversion Ratio (FCR) and the highest Body Weight (BW) were observed in those fed the enriched diet and exposed to normal conditions. Birds at normal stocking density (11.9 birds m-2) had significantly better performance compared with the high stocking density (16.66 birds m-2). This indicates greater role of stocking density as a stress factor on performance. Broiler LBW, BWG and feed intake were affected negatively by high stocking density. Similar, results were reported Elwinger (1995), Thomas et al. (2004), Muniz et al. (2006) and El-Gogary and Azzam (2014) indicated that increasing the number of birds per unit depresses growth rate and feed intake. In contrast, Buijs et al. (2009) found that LBW was not significantly different between birds reared at different stocking densities at 39 days of age. Also, FCR was not affected adversely by high stocking density. Similarly, other researchers (Feddes et al., 2002; Galobart and Moran Jr., 2005) concluded that there was no significant effect of stocking density on FCR of broilers. In contrast, Houshmand et al. (2012) and El-Gogary and Azzam (2014) found that during the grower phase, broilers raised at a high density had an inferior FCR compared with birds housed at a normal density.

Blood parameters: The effect of dietary VE levels and stocking density on plasma T3, T4 and corticosterone concentrations are presented in Table 3. There was no a significant effect of VE levels on plasma T4 but high levels on VE increase than other groups. However, plasma T3 level increased significantly (p≤0.05) in response to VE level and the highest levels occurred at 400 mg kg-1 VE. Thiese results were in agreement with previous studies which reported that serum concentration of T3 and T4 were higher with dietary vitamin E treatment (Sahin et al., 2001, 2002).

Table 4: Effect of dietary supplementation with vitamin E and stocking density on some blood plasma constituents in broilers chickens
Image for - Influence of Vitamin E Supplementation and Stocking Density on Performance, 
  Thyroid Status, Some Blood Parameters, Immunity and Antioxidant Status in Broiler 
  Chickens
a-bMeans in the same Colum with different superscripts differ significantly (p≤0.05)

Also, Gruzauskas et al. (2014) showed that triiodothyronine level in blood of broiler chickens in experimental groups contained VE increased compared with the control group (p>0.05). No significant effects of stocking density on plasma thyroid hormones. This result is in agreement with other studies reported that stocking density did not affect plasma levels triiodothyronine and thyroxine (Tong et al., 2012; El-Gogary and Azzam, 2014). Plasma corticosterone decreased significantly in response to dietary VE and the lowest level occurred at 300 mg kg-1. A reduction in ACTH concentration in plasma from antioxidant supplemented animals was observed by Butterweck et al. (2004) in rats. Taniguchi et al. (2001) found that broiler chickens supplemented with vitamin E had reduced corticosterone content in the adrenal glands. Also, ACTH concentration in serum was lower in supplemental dietary vitamin E groups compared with control. These results are in agreement with the findings by Lin et al. (2006) who showed that corticosterone concentration on day 42 increase ofas stocking density (Lin et al., 2006). However, disagreement with the current result, Turkyilmaz (2008) found that stocking density had no significant effect on blood corticosterone concentration in broiler chickens. There was a trend toward increasing corticosterone concentration with higher stocking density with a statistical significant increase in blood corticosterone concentration in the high stocking density groups.

The effects of vitamin E and stocking density on the plasma concentrations of total protein, albumin, total lipids, cholesterol, high density lipoprotein cholesterol (HDL) and low density lipoprotein cholesterol (LDL) are presented in Table 4. Blood plasma concentrations of total lipids, cholesterol and HDL did not differ significantly between all treatment groups. These results are in agreement with those by Arslan et al. (2001) who showed that no significant difference in plasma cholesterol level between control and vitamin E groups.

Table 5: Effect of dietary supplementation with vitamin E and stocking density on plasma concentrations of SOD, MDA, NDV and AF in broiler chickens
Image for - Influence of Vitamin E Supplementation and Stocking Density on Performance, 
  Thyroid Status, Some Blood Parameters, Immunity and Antioxidant Status in Broiler 
  Chickens
a-dMeans with different superscripts differ significantly

In addition, plasma LDL level was lower at 300 mg kg-1 vitamin E supplementation but plasma Total Protein (TP) and albumin (Alb) levels were higher at 300 mg kg-1 vitamin E supplementation. These results are in agreement with other studies (Sahin et al., 2002) found that plasma protein and albumin concentrations increased linearly with dietary vitamin E supplementation. However, Arslan et al. (2001) found insignificant effect in plasma total protein between control and supplemental vitamin E levels. Results showed also that stocking density had a significant effect on plasma TP, TL and Chol, while plasma albumin, LDL and HDL was not influenced. It appears that plasma lipids were influenced positively by stocking density which may be related to the increased concentration of corticosterone indicative of an adverse effect of stocking density on plasma lipids profile. It is well known that high plasma corticosterone level enhances gluconeogenesis and lipolysis (Whittow, 2000) which may explain the higher levels of TL and Chol (p≤0.05) and also LDL and HDL although they lacked the significant level.

The results relating to the influence of dietary supplementation of vitamin E and stock density on superoxide dismutase (SOD), malondialdehyde (MDA), antibody titers against Newcastle Disease Virus (NDV) and Avian Flu virus (AF) in plasma are shown in Table 5. In this study, the supplementation of vitamin E levels significantly increased SOD compared to the control group. These results are in agreement with other studies (Tras et al., 2000) which demonstrated that vitamin E plus selenium supplementation increased the serum superoxide dismutase level. The plasma MDA was found to be significantly lower in the groups fed enriched diets with vitamin E compared to the control diet. Sahin et al. (2001) and Hosseini-Mansoub et al. (2010) showed that serummal on dialdehyde was significantly lower in groups fed vitamin E. The vitamin E diminishes the peroxidation of polyunsaturated fatty acids via scavenging free radicals (McDowell, 1989; Packer and Landvik, 1990). The present results showed that the antibody titer against NDV and AF in blood plasma of vitamin E treated broiler chickens were significantly higher compared with that of the control group. Lin and Chang (2006) findings suggest that moderate supplementation of vitamin E may enhance immune responses to selective antigens in cockerels but excessive vitamin E may depress specific immune response which is the case in our study. No significant effects of stocking density on plasma SOD but levels of MDA increased by increasing stocking density. Physiological stress (as a result of increasing stocking density) if the stocking density is too high, the temperature may rise dangerously since there will be more metabolic heat being added to the house air than was planned for. It is well known that heat causes an increased production of MDA (Sahin et al., 2001; Naziroglu et al., 2000; Halliwell and Gutteridge, 1989). There were significant lowering effect of stocking density on Ab titers against NDV and AF. Erisir and Erisir (2002) reported that there was a significant decrease in immune response with an increase in stocking density in Japanese quails. Tufft and Nockels (1991) also reported that a decrease in space allowance made broilers more susceptible to infections. However, other disagreements result (Turkyilmaz, 2008) demonstrated that stocking density had no effect on immune response in broilers which is similar to those reported by Hocking et al. (2002) who found that immune function was not affected by food restriction inbroiler breeders.

CONCLUSION

The findings of present study suggest that addition of vitamin E at a level of 300 mg kg-1 diet has a positive effect on productive performance, immune responses and antioxidative status of broiler chickens.

REFERENCES

1:  Abreu, I.A. and D.E. Cabelli, 2010. Superoxide dismutases: A review of the metal-associated mechanistic variations. Biochimica Biophysica Acta (BBA)-Proteins Proteomics, 1804: 263-274.
CrossRef  |  Direct Link  |  

2:  Ajuyah, A.O., R.T. Hardin and J.S. Sim, 1993. Effect of dietary full-fat flax seed with and without antioxidant on the fatty acid composition of major lipid classes of chicken meats. Poult. Sci., 72: 125-136.
PubMed  |  

3:  Allain, C.C., L.S. Poon, C.S.G. Chan, W. Richmond and P.C. Fu, 1974. Enzymatic determination of total serum cholesterol. Clin. Chem., 20: 470-475.
CrossRef  |  PubMed  |  Direct Link  |  

4:  Arslan, M., M. Ozcan, E. Matur, U. Cotelioglu and E. Ergul, 2001. The effects of vitamin E on some blood parameters in broilers. Turk J. Vet. Anim. Sci., 25: 711-716.
Direct Link  |  

5:  Butterweck, V., M. Hegger and H. Winterhoff, 2004. Flavonoids of St. John's Wort reduce HPA axis function in the rat. Planta Medica, 70: 1008-1011.
CrossRef  |  PubMed  |  

6:  Bou, R., F. Guardiola, A. Tres, A.C. Barroeta and R. Codony, 2004. Effect of dietary fish oil, α-tocopheryl acetate and zinc supplementation on the composition and consumer acceptability of chicken meat. Poult. Sci., 83: 282-292.
CrossRef  |  Direct Link  |  

7:  Britton, K.E., V. Quinn, B.L. Brown and R.P. Ekins, 1975. A strategy for thyroid function tests. Br. Med. J., 3: 350-352.
CrossRef  |  Direct Link  |  

8:  Coetzee, G.J.M. and L.C. Hoffman, 2001. Effect of dietary vitamin E on the performance of broilers and quality of broiler meat during refrigerated and frozen storage. S. Afr. J. Anim. Sci., 31: 158-173.
Direct Link  |  

9:  Cordis, G.A., D.K. Das and W. Riedel, 1998. High-performance liquid chromatographic peak identification of 2,4-dinitrophenylhydrazine derivatives of lipid peroxidation aldehydes by photodiode array detection. J. Chromatogr. A, 798: 117-123.
CrossRef  |  Direct Link  |  

10:  Doumas, B.T., D.D. Bayse, R.J. Carter, T. Peters Jr. and R. Schaffer, 1981. A candidate reference method for determination of total protein in serum. I. Development and validation. Clin. Chem., 27: 1642-1650.
PubMed  |  Direct Link  |  

11:  Doumas, B.T., W.A. Watson and H.G. Biggs, 1971. Albumin standards and the measurement of serum albumin with bromcresol green. Clin. Chim. Acta, 31: 87-96.
CrossRef  |  PubMed  |  Direct Link  |  

12:  Duncan, D.B., 1955. Multiple range and multiple F tests. Biometrics, 11: 1-42.
CrossRef  |  Direct Link  |  

13:  El-Gogary, M.R. and M.M. Azzam, 2014. Effects of dietary tryptophan levels and stocking density during the growing-finishing phase on broiler performance and immunity. Asian J. Anim. Vet. Adv., 9: 568-577.
CrossRef  |  Direct Link  |  

14:  Elwinger, K., 1995. Broiler production under varying population densities: A field study. Archiv Geflugelkunde, 59: 209-215.

15:  Erisir, M. and Z. Erisir, 2002. [Changes in some biochemical blood parameters of quails (Coturnix coturnix Japonica) with increasing stocking density]. Turk. J. Vet. Anim. Sci., 26: 491-496, (In Turkish).
Direct Link  |  

16:  Estevez, I., 2007. Density allowances for broilers: Where to set the limits? Poult. Sci., 86: 1265-1272.
CrossRef  |  Direct Link  |  

17:  Feddes, J.J., E.J. Emmanuel and M.J. Zuidhoft, 2002. Broiler performance, body weight variance, feed and water intake and carcass quality at different stocking densities. Poult. Sci., 81: 774-779.
CrossRef  |  Direct Link  |  

18:  Frings, C.S. and R.T. Dunn, 1970. A colorimetric method for determination of total serum lipids based on the sulfo-phospho-vanillin reaction. Am. J. Clin. Pathol., 53: 89-91.
PubMed  |  

19:  Galobart, J. and E.T. Moran Jr., 2005. Influence of stocking density and feed pellet quality on heat stressed broilers from 6 to 8 weeks of age. Int. J. Poult. Sci., 4: 55-59.
CrossRef  |  Direct Link  |  

20:  Greene, J.A., R.M. McCracken and R.T. Evans, 1985. A contact dermatitis of broilers-clinical and pathological findings. Avian Pathol., 14: 23-38.
CrossRef  |  Direct Link  |  

21:  Gruzauskas, R., T. Barstys, A. Raceviciute-Stupeliene, V. Kliseviciute, V. Buckiuniene and S. Bliznikas, 2014. The effect of sodium selenite, selenium methionine and vitamin E on productivity, digestive processes and physiologic condition of broiler chickens. Vet. Med. Zoot., 65: 22-29.
Direct Link  |  

22:  Halliwell, B. and J.M.C. Gutteridge, 1989. Free Radicals in Biology and Medicine. 2nd Edn., Oxford University Press, New York

23:  Heckert, R.A., I. Estevez, E. Russek-Cohen and R. Pettit-Riley, 2002. Effects of density and perch availability on the immune status of broilers. Poult. Sci., 81: 451-457.
CrossRef  |  PubMed  |  Direct Link  |  

24:  Herrera, E. and C. Barbas, 2001. Vitamin E: Action, metabolism and perspectives. J. Physiol. Biochem., 57: 43-56.
CrossRef  |  PubMed  |  Direct Link  |  

25:  Hocking, P.M., M.H. Maxwell, G.W. Robertson and M.A. Mitchell, 2002. Welfare assessment of broiler breeders that are food restricted after peak rate of lay. Br. Poult. Sci., 43: 5-15.
CrossRef  |  Direct Link  |  

26:  Houshmand, M., K. Azhar, I. Zulkifli, M.H. Bejo and A. Kamyab, 2012. Effects of prebiotic, protein level and stocking density on performance, immunity and stress indicators of broilers. Poult. Sci., 91: 393-401.
CrossRef  |  PubMed  |  Direct Link  |  

27:  Lin, H., E. Decuypere and J. Buyse, 2006. Acute heat stress induces oxidative stress in broiler chickens. Comp. Biochem. Physiol. Part A: Mol. Integr. Physiol., 144: 11-17.
CrossRef  |  PubMed  |  Direct Link  |  

28:  Lin, Y.F. and S.J. Chang, 2006. Effect of dietary vitamin E on growth performance and immune response of breeder chickens. Asian-Aust. J. Anim. Sci., 19: 884-891.
Direct Link  |  

29:  Hosseini-Mansoub, N., S.C. Chekani-Azar, A.A. Tehrani, A. Lotfi and M. Manesh, 2010. Influence of dietary vitamin E and zinc on performance, oxidative stability and some blood measures of broiler chickens reared under heat stress (35°C). J. Agrobiol., 27: 103-110.
CrossRef  |  Direct Link  |  

30:  McDowell, L.R., 1989. Vitamins in Animal Nutrition: Comparative Aspects to Human Nutrition. In: Vitamin A and E, McDowell, L.R. (Ed.). Academic Press, London, pp: 93-131

31:  McIlroy, S.G., E.A. Goodall and C.H. McMurray, 1987. A contact dermatitis of broilers-epidemiological findings. Avian Pathol., 16: 93-105.
CrossRef  |  PubMed  |  Direct Link  |  

32:  Naziroglu, M., K. Sahin, H. Simsek, N. Aydilek and O.N. Ertas, 2000. The effects of food withdrawal and darkening on lipid peroxidation of laying hens in high ambient temperatures. Dtsch Tierarztl Wochenschr, 107: 199-202.
PubMed  |  

33:  Misra, H.P. and I. Fridovich, 1972. The role of superoxide anion in the autoxidation of epinephrine and a simple assay for superoxide dismutase. J. Biol. Chem., 247: 3170-3175.
PubMed  |  Direct Link  |  

34:  Myers, G.L., G.R. Cooper, L.O. Henderson, D.J. Hassemer and M. Kimberly, 1994. Standardization of Lipid and Lipoprotein Measurements. In: Laboratory Measurement of Lipids, Lipoproteins and Apolipoproteins, Rifai, N. and G.R. Warnick (Eds.). AACC Press, Washington, DC., USA., pp: 177-205

35:  Muniz, E.C., V.P. Fascina, P.P. Pires, A.S. Carrijo and E.B. Guimaraes, 2006. Histomorphology of bursa of fabricius: Effects of stock densities on commercial broilers. Br. J. Poult. Sci., 8: 217-220.
CrossRef  |  

36:  NRC., 1994. Metabolic Modifiers: Effects on the Nutrient Requirements of Food-Producing Animals. National Academy Press, Washington, DC

37:  Packer, L. and S. Landvik, 1990. Vitamin E in Biological Systems. In: Antioxidants in Therapy and Preventive Medicine, Emerit, I., L. Packer and C. Auclair (Eds.). Springer, New York, USA., ISBN-13: 9781468457322, pp: 93-103

38:  Packer, L., 1991. Protective role of vitamin E in biological systems. Am. J. Clin. Nutr., 53: 1050S-1055S.
Direct Link  |  

39:  Pilz, J., I. Meineke and C.H. Gleiter, 2000. Measurement of free and bound malondialdehyde in plasma by high-performance liquid chromatography as the 2,4-dinitrophenylhydrazine derivative. J. Chromatogr. B: Biomed. Sci. Applic., 742: 315-325.
CrossRef  |  Direct Link  |  

40:  Proudfoot, F.G., H.W. Hulan and D.R. Ramey, 1979. The effect of four stocking densities on broiler carcass grade, the incidence of breast blisters and other performance traits. Poult. Sci., 58: 791-793.
CrossRef  |  Direct Link  |  

41:  Putnam, M.E. and N. Comben, 1987. Vitamin E. Vet. Rec., 121: 541-545.
PubMed  |  

42:  Sahin, K., N. Sahin, M. Onderci, S. Yaralioglu and O. Kucuk, 2001. Protective role of supplemental vitamin E on lipid peroxidation, vitamins E, A and some mineral concentrations of broilers reared under heat stress. Vet. Med., 46: 140-144.
CrossRef  |  Direct Link  |  

43:  Sahin, K., O. Kucuk, N. Sahin and M.F. Gursu, 2002. Optimal dietary concentration of vitamin E for alleviating the effect of heat stress on performance, thyroid status, ACTH and some serum metabolite and mineral concentrations in broilers. Vet. Med., 47: 110-116.
CrossRef  |  Direct Link  |  

44:  SAS., 1996. SAS User's Guide: Statistics. SAS Institute Inc., Cary, North Carolina, USA

45:  Satterlee, D.G., R.B. Abdullah and R.P. Gildersleeve, 1980. Plasma corticosterone radioimmunoassay and levels in the neonate chick. Poult. Sci., 59: 900-905.
CrossRef  |  PubMed  |  

46:  Whittow, G.C., 2000. Sturkie's Avian Physiology. 5th Edn., Academic Press, San Diego, CA., USA., ISBN-13: 9780127476056, Pages: 685

47:  Thaxton, J.P., W.A. Dozier, S.L. Branton, G.W. Morgan and D.W. Miles et al., 2006. Stocking density and physiological adaptive responses of broilers. Poult. Sci., 85: 819-824.
PubMed  |  

48:  Thomas, D.G., V. Ravindran, D.V. Thomas, B.J. Camden, Y.H. Cottam, P.C.H. Morel and C.J. Cook, 2004. Influence of stocking density on the performance, carcass characteristics and selected welfare indicators of broiler chickens. N. Z. Vet. J., 52: 76-81.
CrossRef  |  PubMed  |  Direct Link  |  

49:  Tong, H.B., J. Lu, J.M. Zou, Q. Wang and S.R. Shi, 2012. Effects of stocking density on growth performance, carcass yield and immune status of a local chicken breed. Poult. Sci., 91: 667-673.
CrossRef  |  Direct Link  |  

50:  Traber, M.G. and J. Atkinson, 2007. Vitamin E, antioxidant and nothing more. Free Radical Biol. Med., 43: 4-15.
CrossRef  |  Direct Link  |  

51:  Tras, B., F. Inal, A.L. Bas, V. Altunok, M. Elmas and E. Yazar, 2000. Effects of continuous supplementations of ascorbic acid, aspirin, vitamin E and selenium on some haematological parameters and serum superoxide dismutase level in broiler chickens. Br. Poult. Sci., 41: 664-666.
CrossRef  |  Direct Link  |  

52:  Tufft, L.S. and C.F., Nockels, 1991. The effects of stress, Escherichia coli, dietary ethylenediaminetetraacetic acid and their interaction on tissue trace elements in chicks. Poult. Sci., 70: 2439-2449.
CrossRef  |  PubMed  |  Direct Link  |  

53:  Taniguchi, N., A. Ohtsuka and K. Hayashi, 2001. A high dose of vitamin E inhibits adrenal corticosterone synthesis in chickens treated with ACTH. J. Nutr. Sci. Vitaminol., 47: 40-46.
PubMed  |  

54:  Turkyilmaz, M.K., 2008. The effect of stocking density on stress reaction in broiler chickens during summer. Turk. J. Vet. Anim. Sci., 32: 31-36.
Direct Link  |  

55:  Uchiyama, M. and M. Mihara, 1978. Determination of malonaldehyde precursor in tissues by thiobarbituric acid test. Anal. Biochem., 86: 271-278.
CrossRef  |  Direct Link  |  

56:  Van der Zijpp, A.J., K. Frankena, J. Boneschanscher and M.G. Nieuwland, 1983. Genetic analysis of primary and secondary immune responses in the chicken. Poult. Sci., 62: 565-572.
CrossRef  |  PubMed  |  Direct Link  |  

57:  Wefers, H. and H. Sies, 1988. The protection by ascorbate and glutathione against microsomal lipid peroxidation is dependent on vitamin E. Eur. J. Biochem., 174: 353-357.
CrossRef  |  PubMed  |  Direct Link  |  

58:  Wegmann, T.G. and O. Smithies, 1966. A simple hemagglutination system requiring small amounts of red cells and antibodies. Transfusion, 6: 67-73.
CrossRef  |  Direct Link  |  

59:  Mahima, A.M. Ingle, A.K. Verma, R. Tiwari and K. Karthik et al., 2013. Immunomodulators in day to day life: A review. Pak. J. Biol. Sci., 16: 826-843.
CrossRef  |  Direct Link  |  

60:  Buijs, S., L. Keeling, S. Rettenbacher, E. Van Poucke and F.A.M. Tuyttens, 2009. Stocking density effects on broiler welfare: Identifying sensitive ranges for different indicators. Poult. Sci., 88: 1536-1543.
CrossRef  |  Direct Link  |  

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