The Effects of Selenium Supplementation on Performance and Antioxidant Enzyme Activity in Broiler Chickens

Abstract

In August 2000, organic selenium in a selenized yeast, (Sel-Plex©, Alltech Biotechnology Center, Nicholasville, KY) that contained high levels of selenomethionine was approved by the United States Food and Drug Administration as a source of selenium (Se) supplementation for broiler chickens. The previously reported positive responses to the presence of selenomethionine in Se yeast supplemented feed have increased the interest in use of organic Se in all phases of poultry production. Thus, a series of experiments were conducted to compare the influences of organic and inorganic sources of Se (Se yeast or sodium selenite) on production performance parameters. Body weights, feed conversion ratio (FCR), cut up parts yield as a percentage of carcass weight, drip loss from breast meat, and serum thyroid hormones were measured up to 6 weeks of age.

Body weight at 42 days was increased in Se yeast fed broilers as compared to those in the no supplemental Se or sodium selenite treatment groups. The combination of sodium selenite and selenized yeast was no more effective than selenized yeast alone on body weight. FCR were improved by all Se sources, with the selenized yeast and selenized yeast + sodium selenite treatments being superior to sodium selenite only fed birds.

On a percentage of carcass weight, yields of viscera, feet and neck were higher in selenized yeast treated birds. Yields of leg and pectoralis major, as percentages of carcass weight, were increased and decreased, respectively, in the selenized yeast treated birds. There was an increase in breast meat drip loss when birds were fed sodium selenite as compared to those fed the selenized yeast or no supplemental Se treatments, suggesting that prooxidant properties of sodium selenite supplementation may be associated with increased moisture loss from processed breast meat.

The serum T4 levels were higher in birds within the no supplemental Se treatment as compared to those supplemented with sodium selenite or selenized yeast. The ratios between serum T4 and T3 indicate that selenized yeast treatment facilitated the extra-thyroidal conversion of T4 to T3.

The Se status of broilers influenced by dietary Se sources may increase the bird's ability to overcome the adverse effects of reactive oxygen metabolites (ROM). The addition of peroxidized fat to poultry diets produces a state of oxidative stress and can increase the level of ROM that must be reduced in the bird. A second study was conducted to evaluate the positive responses to selenized yeast as influenced by an improved status of the antioxidant enzymes, glutathione peroxidase (GSH-Px) and glutathione reductase (GR). This study evaluated the effects of feeding graded levels of oxidized poultry fat on blood and hepatic GSH-Px and hepatic GR activity in broiler chickens given inorganic or organic forms of dietary Se.

Neither fat oxidation nor Se source significantly altered the BW and FCR of broilers, or their activity of hepatic GR. Blood GSH-Px was influenced significantly by both fat and Se source, but the fat X Se source interaction was not significant. There was a Se source effect on the hepatic GSH-Px activity with sodium selenite causing an elevated GSH-Px activity, even in the basal diets with no added oxidized fat. There was no peroxide level effect on GSH-Px in the sodium selenite group, but GSH-Px activity in the Se yeast group did not increase until dietary peroxide level was at the highest inclusion rate.

Because elevated GSH-Px is indicative of oxidative stress, the dietary Se yeast supplementation resulted in better Se status in broilers than in birds fed sodium selenite. Only dietary inclusion of the highest level of oxidized fat was sufficient to impose oxidative stress in the Se-yeast fed birds to induce hepatic GSH-Px activity. These results suggest that the dietary Se supplied in an organic form (selenomethionine) may improve Se status in broilers, leading to greater resistance to oxidative stress than when an inorganic form of Se (sodium selenite) is fed.

The results from these studies suggest that selenomethionine from selenized yeast may be a superior form of Se for poultry. The beneficial effects of selenomethionine on production performance and the antioxidant enzyme profile of broiler chickens appear to support this conclusion.