Comparison of Organic and Mineral Selenium on Performance, Microbial Population, Intestinal Histopathologhy and Cecum Acidity of Laying Hens

[1]Selenium is an essential mineral for many metabolic functions of the body, including the activation of enzymes and the optimal biochemical and physiological function of birds (Antongiovanni et al., 2007). Selenium protects cell membranes from oxidative damage and can therefore improve nutrient efficiency (Arner et al., 2012). The small intestine is the most important part in the digestion and absorption of nutrients, while the large intestine and intestinal tract are very important areas for the accumulation of microbes (Chitra et al., 2013). Gastrointestinal health is one of the most important and effective factors in bird function. Gastrointestinal microbial population affects the nutrition and health of various animal species, including poultry. These microorganisms need trace elements such as selenium to perform their normal metabolic functions. Selenium may affect bacterial cells by disrupting the respiratory chain (Pappas et al., 2005). In addition to improving the quality and composition of intestinal microflora, selenium can have a positive effect on the morphology of the intestine as an antioxidant (Haghighi-khoshkhoo et al., 2010). Despite these benefits, the effect of selenium on intestinal microbial population is largely unknown, so the aim of this study was to investigate the effect of different levels of organic and inorganic selenium in the diet on microbial population, intestinal morphology and intestinal acidity in laying hens.

The experiment was conducted in a completely randomized design with 300 laying hens of high-line strains from 23 to 35 weeks of age with 5 treatments, 6 replications and 10 hens per replication. Experimental treatments include 1- Base diet (without selenium), 2- Base diet + 0.5 mg/kg sodium-selenite, 3- Base diet + mg/kg 1 selenite-sodium, 4- Base diet + mg/kg 0.5 selenium-methionine, 5-base diet + 1 mg/kg selenium-methionine. At the end of the experiment, two birds were randomly selected from each replicate; To evaluate the microbial population, a sample of the contents of the cecum on the culture medium was used (1). Tissue samples were prepared and then measured using a microscope, villi length, villi width, crypt depth, and number of goblet cells (9). To measure acidity, samples were taken from the contents of the cecum, and acidity was measured by a pH meter.

The results indicate that consuming 1 mg/kg of selenium-methionine increased the villi area compared to the control treatment. The experimental treatments did not affect villi length, villi width, crypt depth, number of goblet cells, and the ratio of villus length to crypt depth. The consumption of 1 mg/kg of selenium-methionine significantly decreased the population of Salmonella and increased the population of Lactobacillus in the cecal compared to other experimental treatments. The consumption of 0.5 and 1 mg/kg of selenium-methionine caused a significant decrease in the population of aerobic bacteria compared to the control treatment. The acidity of cecal contents in the treatment containing 1 mg/kg of selenium-methionine was significantly reduced compared to the control treatment. Several studies (Langhout et al., 1999, Lukaszewicz et al., 2011, Pappas et al., 2005) have reported that using organic sources of selenium reduces the coliform population. In mice, dogs, and laying hens, selenium intake has been shown to increase the number of Lactobacillus and decrease Escherichia coli and Staphylococcus aureus in the cecum (Langhout et al., 1999, Lukaszewicz et al., 2011, Pappas et al., 2005). Increasing the population of beneficial bacteria due to the provision of sufficient selenium for their synthesis is also an antioxidant property of selenium in preserving the life of these bacteria. It appears that beneficial bacteria, such as Lactobacillus, can competitively eliminate harmful bacteria such as Escherichia coli in the gut (Lukaszewicz et al., 2011). An increase in the number of pathogenic bacteria in the intestine causes the villi to shorten and the lining to shrink (Attia et al., 2010).Numerous studies demonstrate that the consumption of diets containing selenium compounds has destructive effects on harmful intestinal bacteria (Chantiratikul et al., 2008, Hashemi et al., 2012, Heindl et al., 2010, Horn et al., 2009, Langhout et al., 1999). Adding organic selenium to the diet of broilers increases the weight of the intestines due to the growth of villi and intestinal lamina propria (Haghighi-khoshkhoo et al., 2010, Heindl et al., 2010). The lack of selenium consumption on morphology can be attributed to the levels of selenium used, as well as the bird's lack of stress. Selenium can exert its effect more effectively under stress conditions. Most harmful bacteria grow in an environment with acidity close to 7 or slightly higher, while beneficial bacteria multiply in an acidic environment and compete with pathogenic bacteria (Cooke et al. 1973). An increase in acidity leads to a decrease in Escherichia coli and Salmonella in the gastrointestinal tract. Therefore, the consumption of organic sources of selenium reduces the population of pathogenic microorganisms (aerobic bacteria, Escherichia coli, and Salmonella) and increases the population of Lactobacillus competitively, followed by an increase in gastrointestinal acidity. This improvement may lead to an increase in digestion, absorption, and performance (Kasaikina et al., 2011).

 According to the results of this study, it can be said that consuming organic sources of selenium (levels of one and 0.5 mg of selenium-methionine per kg of feed) significantly reduces the population of harmful aerobic bacteria, bacteria. Salmonella and Escherichia coli and cause a competitive increase in the beneficial population of Lactobacillus; The consequence of this operation is to increase the acidity of the cecum and reduce the damage and microbial destruction to the intestinal tissue, and therefore with positive changes in the morphology of the small intestine will lead to improved bird function.