Selenium Supplementation and Antioxidant Protection in Broiler Chickens.

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Title: Selenium Supplementation and Antioxidant Protection in Broiler Chickens.
Author: Gowdy, Kymberly Mae
Advisors: Dr. Frank W. Edens, Committee Chair
Abstract: Selenium supplementation in poultry has long been associated with energy metabolism, increased feed efficiency, improved reproduction, and improved immune responses. Poultry are constantly exposed to environmental stressors that require the antioxidant protection of selenium supplementation. Improved performance results in an improved product for the industry to thrive on. However, the debate has now come up to examine the selenium dose and chemical form that is commonly fed to poultry amongst other livestock. The inorganic forms of selenium commonly used have proven to have prooxidant properties and can be toxic at high levels. Organic forms of selenium, such as Sel-Plex®, have been shown to be generally safer and better absorbed. These developments raise questions as to which form of Se is best for dietary supplementation. Herein, studies were designed to investigate three main areas associated with the different forms of selenium supplementation. 1) Effect of various selenium supplements on antibody and nitrite production in commercial broilers, 2) Effects of high levels of selenium supplements on the developing immune system, 3) Effects of selenium supplementation on a new selenoprotein, thioredoxin reductase. Selenium supplementation with selenite or Sel-Plex® did show varying effects on the humoral and innate immune response. Birds fed diets with selenium overall had higher antibody titer that was maintained longer than birds not fed selenium supplemented diets. Birds fed selenite diets generally had significantly higher IgM titers, while birds fed Sel-Plex® diets had significantly higher IgG titers. When nitrite values were examined, birds fed selenium-supplemented diets had lower resting values and higher values when macrophages were stimulated with LPS. The control fed birds had higher resting values and lower values when stimulated with LPS. This could be due to an enhancement of the immune system with selenium in the diet. However, selenite fed birds had significantly higher nitrite values that indicate prooxidant properties potentially damaging to cells. High levels of inorganic or organic forms of selenium showed different effects on the developing immune system. At levels as low as 1.2 ppm of selenite, immune organ weights were significantly decreased and inflammatory responses were increased. Up to 15 ppm no signs of toxicity were noted with the organic supplement Sel-Plex®. This indicates that at high levels of dietary inclusion, Sel-Plex® has no detrimental effects on the immune system. Selenium is an integral part of a range of selenoproteins. Thioredoxin reductase (TR) is one of those proteins, which is a key player in the antioxidant cascade. TR has been purified and characterized in many organisms but not the chicken. Chickens are exposed to many stressors, so it is of great importance to study this enzyme in chickens. The distribution of TR protein expression was uniform throughout the chicken's body, regardless of selenium supplementation. However, varying isoforms did appear that were not seen in mammalian tissues. When activity of TR was examined, significant differences were seen among treatments, with the highest activities in the Sel-Plex® fed birds. The subcellular distribution of this enzyme showed majority of the activity to be in the mitochondrial fractions, while there was little to no protein expression in these fractions. All of this taken together indicates that chicken TR may be very different than mammalian TR, but further studies are needed to draw these conclusions. . Attempts to purify TR from chicken liver were also made. The enzyme seemed to be dependent on selenium supplementation, age of the bird and the addition of FAD. Ammonium sulfate saturation of the enzyme caused it to fall out of solution at 70% instead of 80% like the mammal. Reduction with 0.2 M DTT did not restore activity after being dialysed overnight. All of these results indicate that chicken TR is very sensitive to enzymatic conditions and is not very stable. Purifying this enzyme from chickens could be a great benefit to poultry science. The emphasis of this thesis is on the different supplemental forms of Se and their effects on broiler health. Selenium is essential whether it be for immune responses or antioxidant protection. However, careful consideration needs to be made when choosing an optimum form. Organic forms have proven to be more beneficial to the poultry immune system through many different aspects.
Date: 2004-10-06
Degree: MS
Discipline: Immunology

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