International Journal of Poultry Science 7 (8): 798-805, 2008 ISSN 1682-8356 © Asian Network for Scientific Information, 2008 798 Selenium Yeast Effect on Broiler Performance 1 J. Robert Upton , Frank W. Edens and Peter R. Ferket 2,3 3,4 3 Syngenta Animal Nutrition, Research Triangle Park, NC 27709, USA 2 Department of Poultry Science, North Carolina State University, Raleigh, NC 27695, USA 3 Abstract: Positive responses attributed to selenomethionine in Se-yeast (Sel-Plex [SP], Alltech, Inc., TM Nicholasville, KY 40356)-supplemented feed have increased the interest in use of SP in all phases of poultry production. Experiments to test the influence of SP on performance parameters in broiler males (Arbor Acres X Arbor Acres) in floor pens were conducted. A completely randomized experimental design incorporated four Se-supplementation treatment groups [(1) No Se, (2) sodium selenite (NaSe; 0.2 ppm), (3) SP (0.2 ppm), and (4) NaSe (0.1 ppm)+SP (0.1 ppm)]. Body weights (BW), feed conversions (FCR), cut-up carcass yield, breast meat drip loss and serum thyroid hormones were measured through 6 wk of age. BW of SP-fed broilers were increased compared to No Se or NaSe treatment groups and the combination of NaSe and SP was no more effective than SP alone. FCR improved with Se supplementation with the SP and SP+NaSe being superior to NaSe only treatment. Feather yield was increased by SP treatment compared to all other treatments. Carcass weight, yields of viscera, feet, leg and thigh and neck were higher in SP-treated birds Increased breast meat drip loss was induced by NaSe. The serum thyroxin (T ) levels were higher in birds 4 within No Se treatment as compared to NaSe or SP. The ratios between serum T and tri-iodothyronine (T ) 4 3 indicate that SP treatment facilitated the conversion of T to T . The results suggest that Se from SP was used 4 3 more efficiently for performance in fast growing, high yielding broiler chickens. Key words: Selenium, broiler, performance, yield, thyroid hormones Introduction In, 1818, the Swedish chemist, Berzelius, discovered selenium (Se) and determined that it was an element closely associated with sulfur and tellurium. Unfortunately, the biological significance of this element was not recognized until it was identified as the toxic agent linked with “alkali disease” or selenosis, in the Dakota and Wyoming territories in the United States (Franke, 1934). Until, 1957, Se was considered to be a dangerous element, but Schwarz and Foltz (1957) found Se to be an essential dietary nutrient that prevented nutritional liver necrosis in rats. In the same year, prevention of exudative diathesis by Se was reported in chicks (Patterson et al., 1957). Nutritionists soon initiated extensive studies to discover the metabolic function (s) of Se and document the consequences of its deficiency in human and animal diets. Se deficiency manifests itself in poultry in many diseases and dysfunctions including liver necrosis, muscular dystrophy, microangiopathy, exudative diathesis, pancreatic fibrosis, poor feathering, immune deficiency, reduced hatchability and many others (Edens, 1996). The signs of Se deficiency in chickens have been related to the role of Se in antioxidant protection via the enzyme glutathione peroxidase (GSH-px). For many years, this was the only known role of Se in any species. More recently, a number of selenoproteins have been identified that both expand our knowledge of the physiological function of Se and aid in explaining other signs of Se deficiency (Arthur, 1997; Jacques, 2001; Edens and Gowdy, 2005). Due to the similarities between Se and sulfur, it has been a long held belief that Se would follow sulfur pathways in its metabolism. Burnell and Whatley (1977) strengthened this concept when they reported that plants and bacteria metabolize Se to the organic selenomethionine and selenocysteine. Seleno- methionine is readily utilized as a substrate by enzymes that use methionine and selenomethionine may even be more available than pure methionine (Markham et al., 1980). It has been accepted for many years that the selenoamino acids: selenomethionine, selenocysteine, and selenocystine, are the primary sources of naturally occurring Se in plant-based (Burk, 1976) and meat- based (Levander, 1986; Cai et al., 1995) feed ingredients. The selenoamino acids are bound in protein, predominantly as selenomethionine and selenocysteine and can constitute up to 80% of the total Se in plants, grains (Butler and Peterson, 1967) and in Sel-Plex , the organic Se-yeast (Kelly and Power, 1995). TM In June, 2000, the United States FDA approved selenium yeast (Sel-Plex , SP) as an organic Se source for the TM use in broiler chickens. Conventionally, Se has been supplemented in animal feeds in the inorganic form as sodium selenite (NaSe). SP affords a mixture of organic Se compounds (Kelly and Power, 1995), but the primary form is selenomethionine in the yeast cellular protein