عنوان مقاله [English]
Selenium is a mineral that is essential for many metabolic functions of the body, including the activation of enzymes and the optimal biochemical and physiological function of birds (2). Selenium protects cell membranes from oxidative damage and can therefore improve nutrient efficiency (3). 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 (6). 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 (27). 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 (13). 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.
Materials and Methods
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 and 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; In order 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 pH meter.
Results and Discussion
The results showed that consumption of 1 mg/kg selenium-methionine increased the villi area compared to the control treatment. Villi length, villi width, crypt depth, number of goblet cells and ratio of villus length to crypt depth were not affected by experimental treatments. Consumption of 1 mg/kg selenium-methionine significantly reduced the population of Salmonella and significantly increased the population of Lactobacillus in the cecal compared to other experimental treatments. Consumption of 0.5 and 1 mg/kg 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 selenium-methionine was significantly reduced compared to the control treatment. Many studies (22, 24, 27) have reported that the use of organic sources of selenium reduces the coliform population. It has also been reported that in mice, dogs and laying hens, selenium intake increases the number of Lactobacillus and decreases Escherichia coli and Staphylococcus aureus in the cecum (24, 25, 27). Increasing the population of beneficial bacteria due to the provision of sufficient selenium for the synthesis of these bacteria is also the antioxidant property of selenium in preserving the life of these bacteria. It seems that beneficial bacteria (such as Lactobacillus) can reduce the number of harmful bacteria such as Escherichia coli in the gut by competitively eliminating them (25). Increasing the number of pathogenic bacteria in the intestine causes the villi to shorten and the lining to shrink (4). Numerous studies show that consumption of diets containing selenium compounds has destructive effects on harmful intestinal bacteria (5, 14, 16, 18, 22). Addition of organic selenium to the diet of broilers due to the growth of villi and intestinal lamina propria increases the weight of the intestines (13, 16). 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; Because in selenium under stress conditions can exert its effect more effectively. Most harmful bacteria grow in acidity close to 7 or slightly higher, while beneficial bacteria multiply in an acidic environment and compete with pathogenic bacteria (7). Increased acidity leads to a decrease in Escherichia coli and Salmonella in the gastrointestinal tract. Thus, with the consumption of organic sources of selenium, the population of pathogenic microorganisms (aerobic bacteria, Escherichia coli and Salmonella) decreased and the population of Lactobacillus increased competitively, followed by an increase in gastrointestinal acidity. Improves digestion, absorption and performance (20).
According to the results of this study, it can be said that the consumption of 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.