Selenium as a trace mineral is essential for animals, plants and humans [1, 2]. Schwarz and Foltz first described the preventive effects of selenium in liver necrosis and liver degeneration in a rat model . This historical work caused great interest in the broader scientific community about selenium in animal and human physiological fields. Today it is generally known that selenium may modulate a broad spectrum of key biological processes andplay an important role in imunne system activity, and protect from oxidative damage, including carcinogenesis inhibition. On the other hand, it is also well-known that high selenium doses are dangerous causing several serious health problems.
In chicken breeding, the most important indicators are meat quality and egg quality. Chicken producers worldwide are trying to increase production performance together with reduction in breeding costs .
Koyuturk et al. demonstrated a selenium, vitamin E and vitamin C combination have therapy effect on ethanol-induced duodenal mucosal damages . Meanwhile, some authors, for example Ojuawoand Keith studied the role of serum concentrations of zinc, copper and selenium in children with inflammatory bowel disease .
Littlethought is given to the possibility of influencing the organ system development, which are primarily responsible for chick growing. Small and large bowels are important part of the gastrointestinal system of human/animals with primary involvement in their development. Bowel development with correct villous enzyme activities is in connection with nutrition resorbtion and chicken health status. Some research works have documented the impact of seleniumon enterocytes [7, 8]. Davis et al. demonstrated se-enriched broccoli could decline the intestinal tumorigenesis for multiple intestinal neoplasia mouce . So, we can hypothesise that selenium supplements will have some effects on the growth of bowels, including bowels mucosal epithelial cellular differentiation. Besides, several research studies document positive effects of selenium on chicken health [10, 11], including chicken breeding .
The aim of the current experiment is to test the effects of variable doses fornano-selenium (NS) supplement on the chicken gastrointestinal tract as an animal model.
MATERIALS AND METHODS
This study was conducted in 2016 in a commercial poultry farm at Rasht, Iran. The experiment was approved at Ethics Committee of the Ilam Branch, Islamic Azad University. The study followed International Guidelines for Research (Directive 2010/63/EU).
Animals and housing
In total, 180 male Ross chickens were randomly divided into 6 treatments, with 3 replicates per treatment, with 10 birds for each replicate. One-day-old broilers were purchased and randomly divided into treatments with same body weights. Chicks were reared till 42 day of age based on the starter (1-21 days of age), and the grower (22-42 days of age) periods. Formula and chemical analysis of used diets is shown in Table 1. Broiler chickens received feeds and water ad libitum throughout the trials. Broilers were unable to feed from adjoining cages. The animals were housed in land cages with dimensions of 1.0 x 1.0 m. All broilers had a common environment. Thermo-neutral ambient temperature was maintained in accordance with standard brooding practices. Lighting program was conducted for 23h on 1-7 days of age and 40-42 days of age, and for 20 h/day, with four hours of darkness on 8 -39 days of age. Routine vaccination and de-worming was designed and administered by the farm veterinarian in co-operation with the regional veterinary authority. Vaccination consisted of infectious bronchitis (Infectious Bronchitis Virus (IBV) (H120); Razi Co, Iran) at day 1, Gamboro vaccination (Gamboro (IBD071IR); Razi Co, Iran) at days 14 and 23, Newcastle at days 8 and 21, and influenza at day 1.
A completely randomized design was used, with treatments containing different selenium levels, in three replicate pens of 10 chicks each, in a total of 18 experimental units. Commencing from day one, groups were created as follows. Group 1 (CON) : control birds, Group 2 (NS1) : 0.1, Group 3 (NS2) : 0.2, Group 4 (NS3) : 0.3, Group 5 (NS4) : 0.4 and Group 6 (NS5) : 0.5; (0.1, 0.2, 0.3, 0.4 and 0.5 are mg/kg of feed dietary nano-selenium from 1st-42nd days of age in Groups 2 to 6, respectively).
At the 42nd day of age, 1 bird for each replicate was euthanized. These birds were used for measuring of carcass characteristics. Birds were fully pecked. Feet were separated from the carcass in the tibio-tarsal joint and intestinal segment dimensions were weighted and recorded. The length, width and diameter of duodenum, ileum, jejunum, and colon were measured. All dimensions were rounded to integers. Total weight of each segment was related to the totally eviscerated carcass. Ratios were calculated according to the following formula: [(weight of segment/eviscerated carcass weight) × 100].
Data were analyzed using GLM. The significance of the differences between group means was analysed using the ANOVA procedure, followed by a Tukey’s post hoc test, using IBM SPSS Statistics 21 software . P values ≤ 0.05 were considered as statistically significant.
RESULTS AND DISCUSSION
All the achieved results are summarized in Tables 2-5. Usually bowels dynamically react to nutrition. The most dramatic changes usually occur in the duodenum . Our experiment also showed that selenium has the biggest impact on duodenum weight, duodenum length and duodenum width, as compared to the control group.
The results document the positive effect of selenium supplement on duodenum with weight decreasing and simultaneously length increasing. The results of jejunum and ileum show the same trends, but the measured levels are not so clear, comparing results of duodenum.
Also nano-selenium improved the function of the large bowel (colon). The increase in length, width, diameter, and weight of colon in nano-selenium chicken consumer groups was seen in the results.
Small and large bowel length increase is in direct relationship with better resorbtion. These results indicate that this parameter is important for chicken breeding industry.
Gastrointestinal homeostasis is one of the conditions for normal chicken production. Several references prove that selenium deficiency can cause intestinal mucosal inflammation . The works of Wang et al. show that selenium deficiency induces degranulation of mast cells in the jejunum of chickens with jejunal mucosal changes with vacuolisation and granulation of the epithelial cells .
This findings also documents the impact of seleniumon bowel mucosa development. Another study showed that dietary supplementation with optimum levels of selenium reduced negative consequences of necroticenterititis induced dimmunopathology . One of the most important problems of poultry breeding is still in higher mortality during initial stages of the breeding. The main cause is heart failure [18, 19].
Another important gastrointestinal problem is increased sensitivity to enteral small bowel, malabsorption syndrome and large bowel infections . These factors significantly affect the productivity and economy of breeding. Necrotic enteritis is one of the main problems of chicken breeders with significant mortality and economical impact on chicken breeding. Nutrition has a big impact to chicken health, including impact on mortality elimination.
Ascites syndrome is one of the most serious health problems of chicken rearing. It is the result of fat, muscle and connective tissue amount increasing in which the heart cannot push sufficient blood through the lungs, leading to ventricular hypertrophy. In our previous work, we have shown that feeding regime has significant effect on the ascites incidence syndrome in chicks . In this sense, there is intensive effort to limit the intense chicken breeding and replace it with natural chicken breeding. This is in relationship with animal welfare . Previous research would indicatedthat it is also supported by several European and non-European countries with financial support for animal breeding.
Selenium plays an important role in chick growing and here we have proved that selenium nano-doses influence small and large bowel growing. Some previosly published articles document important impact of selenium for chicken breeding with imparted resistance to oxidative stress [23, 24] and protective effect of selenium to immunologic injury .
Some researchers have interpreted the positive results of intestinal indicesin the selenium receptor groups that selenium in addition to improving the composition and rate of intestinal microflora, can have a positive effect on the morphology of the intestine (duodenum, jejunum, ileum and colon) as an antioxidant .
This research documents the positive effects to several bowel parameters. The results suggest thatadding nano-selenium doses to chick nutrition would result in improved health and effecient adult chicken production.
Financial support by Ilam Branch, Islamic Azad University is gratefully acknowledged.
CONFLICTS OF INTEREST
The authors report no conflicts of interest.
 Navarro-Alarcon M., Cabrera-Vique C., (2008), Selenium in food and the human body: A review. Sci. Total. Environ. 400: 115-141.
 Fairweather-Tait S. J., Bao Y., Broadley M. R., Collings R., Ford D., Hesketh J. E., Hurst R., (2011), Selenium in human health and disease. Antioxid.Redox Sign. 14: 1337-1383.
 Schwarz K., Foltz C. M., (1957), Selenium as an integral part of factor 3 againtsdieraty necrotic liver degeneration. J. Am. Chem. Soc. 79: 3292-3293.
 Chowdhury V. S., Sultana H., Furuse M., (2014), International perspectives on impacts of reproductive technologies world food production in Asia associated with poultry production. Adv. Exp. Med. Biol. 752: 229-237.
 Misra S., Kwong R. W., Niyogi S., (2012), Transport of selenium across the plasma membrane of primary hepatocytes and enterocytes of rainbow trout. J. Exp. Biol. 215: 1491-1501.
 Thiry C., Ruttens A., Pussemier L., Schneider Y. J., (2013), An in vitro investigation of species-dependent intestinal transport of selenium and the impact of this process on selenium bioavailability. Br. J. Nutr. 109: 2126-2134.
 Davis C. D., Zeng H., Finley J. W., (2002), Selenium-enriched broccoli decreases intestinal tumorigenesis in multiple intestinal neoplasia mice. J. Nutr. 132: 307-309.
 Cao C., Fan R., Chen M., Li X., Xing M., Zhu F., Xue H., Wang K., Xu S., (2017), Inflammatory response occurs in veins of broilers chickens treated with a selenium deficiency diet. Biol. Trace. Elem. Res.158: 176–185.
 Zamani-Moghaddam A. K., Mehraei-Hamzekolaei M. H., Khajali F., Hassanpour H., (2017), Role of selenium from different sources in prevention of pulmonary arterial hypertension syndrome in broiler chickens. Biol. Trace. Elem. Res. 180: 164-170.
 Urso U. R., Dahlke F., Maiorka A., Bueno I. J., Schneider A. F., Surek D., Rocha C., (2015), Vitamin E and selenium in broiler breeder diets: Effect on live performance, hatching process and chick quality. Poult. Sci. 94: 976-983.
 SPSS., (1997), SPSS Base 7.5 for Windows.SPSS, Chicago, IL.
 Makovicky P., Tumova E., Volek Z., Makovicky P., Arnone J. M., Svecova I., Samasca G., (2017), The influence of food restriction on the small bowel: Does intensive short-term food restriction lead to weight loss?. Bratisl. Lek. Lis. 118: 361-365.
 Liu Z., Qu Y., Wang J., Wu R., (2016), Selenium deficiency attenuates chicken duodenal mucosal immunity via activation of the NF-κb Signaling Pathway. Biol. Trace. Elem. Res. 172: 465-473.
 Wang G. O., Wang H. H., Wang H. X., (2012), Effects of Se deficiency on seum histamine concentration and the expression of histamine H2 receptor in the jejunum of chickens. Pol. J. Vet. Sci. 15: 547-552.
 Xu S. Z., Lee S. H., Lillehoj H. S., Bravo D., (2015), Dietary sodium selenite affects host intestinal and systemic immune response and disease susceptibility to necrotic enteritis in commercial broilers. Br. Poult. Sci. 56: 103-112.
 Hassanzadeh M., Buyse J., Toloei T., Decuypere E., (2014), Ascites syndrome in broiler chickens: A review on the aspect on endogenous and exogenous factors interactions. J. Poult. Sci. 51: 229-241.
 Khajali F., Wideman R. F., (2016), Nutritional approaches to ameliorate pulmonary hypertension in broiler chickens. J. Anim. Physiol. Anim. Nutr. 100: 3-14.
 Yegani M., Korver D. R., (2008), Factors affecting intestinal health in poultry. Poult. Sci. 87: 2052-2063.
 Hasani A., Bouyeh M., Rahati M., Seidavi A., Makovicky P., Laudadio V., Tufarelli V., (2018), Which is the best alternative for ascites syndrome prevention in broiler chickens?. Effect of feed form and rearing temperature conditions. J. Appl. Anim. Res. 46: 392-396.
 Riber A. B., Van de Weerd H. A., de Jong I.C., Steenfeldt S., (2018), Review of environmental enrichment for broiler chickens. Poult. Sci. 97: 378-396.
 Mahmound K. Z., Edens F. W., (2017), Influence of organic selenium on hsp70 response of heat-stressed and enteropathogenicEcherichia coli-challenged broiler chickens (Gallus gallus). Comp. Biochem. Physiol. C: Toxicol. Pharmacol. 141: 69-75.
 Yu J., Yao H., Gao X., Zhang Z., Wang J.F., Xu S.W., (2015), The role of nitric oxide and oxidative stress in intestinal damage induced by selenium deficiency in chickens. Biol. Trace. Elem. Res. 163: 144-153.
 He Y., Fang J., Peng X., Cui H., Deng J., Chen Z., Lai W., Shu G., Tang L., (2014), Effects of sodium selenite on aflatoxin B1-induced decrease of ileac T cell and the mRNA contents of IL-2, IL-6, and TNF-α in broilers. Biol. Trace. Elem. Res. 159: 167-173.