Effectivenesss And Bioavailability Of Yeast Selenium For Broiler Chickens Under Normal And Stress Conditions

The study was conducted to evaluate the effects of different levels of sodium selenite and yeast selenium on growth performance,thyroid hormone,antioxidant capacity and selenium content in tissues of Avian broiler chickens under normal and stress conditions in order to reveal the effectiveness and bioavailability of Yeast-Se relative to Na₂SeO₃ for broilers.The results will provide the scientific basis for a reasonable choice between different selenium sources at the different production environment,as well as for development and application of organic selenium product. This study included two trials:Trial 1 the effects of different sources and levels of selenium on performance, antioxidant ability and tissue selenium content of broiler chickens.A total of 216 Avian broiler chickens were used to investigate effects of sodium selenite or yeast selenium on performance,antioxidant ability,thyroid hormones and tissue selenium content.The broilers,which were fed the diet deficient in selenium for two weeks,were allocated to 9 treatments,each of which had 3 pens of 8 chickens per pen.The 9 dietary treatments were basal diet only and basal diet adding 0.1,0.2, 0.3 and 0.4 mg/kg selenium as Na₂SeO₃ or Yeast-Se,respectively.The trial lasted 4 weeks,from D15 to D42.The results showed that(1) supplementation with Se tended to increase ADG and significantly improved feed/gain ratio and optimal Se level for performance was 0.1-0.2 mg/kg.(2) As the Se level elevated,serum T3 concentration increased significantly and T3/T4 tended to increase.(3) As the Se level elevated, antioxidant ability of broilers enhanced significantly,reflected as increase of GSH-Px, SOD,T-AOC and decline in MDA.Optimal Se level for antioxidant capacity was 0.3-0.4 mg/kg.(4) As the Se level elevated,selenium content in serum and tissues of broilers increased significantly and Se deposition was highest at 0.4 mg/kg.(5) The broilers consuming Yeast-Se diets had higher Se deposition in tissue than Na₂SeO₃. But,there was no significant difference between selenium sources in other parameters.Trial 2 the effects of different sources of selenium on performance,antioxidant ability and tissue selenium content of broiler chickens under stress condition and bioavailability of Yeast-SeThis trial was conducted to investigate the effects of adding selenium on stressd broiler chickens and assess the relative bioavailability values of Yeast-Se for normal and stressed chickens.A total of 240 Avian broiler chickens,14 d of age,were allocated to 10 treatments by 2×3×2 factorial design,including two Se sources (sodium selenite or yeast selenium),three levels(0,0.1,0.4 mg/kg,0 level shared by two sources) and two conditions(normal or stress induced by adding 20 mg/kg corticosterone in basal diet),each of which had 3 pens of 8 chickens per pen.The trial lasted 2 weeks to 28 d of age.The results showed that(1) supplementation of corticosterone in diet induced physiological stress successfully,and then caused oxidative injury in chickens,reflected as the significant increase in malondialdehyde. (2) As the Se level elevated,feed conversion of stressed broilers was improved and the best effect was gained at 0.4 mg/kg Yeast-Se.(3) As the Se level elevated,the concentration of corticosterone and uric acid and creatine kinase activity decreased in serum,while T3,T3/T4 and cytochrome C oxidase of stressed broilers tended to be improved,indicating the anti-stress effects of selenium.(4) As the Se level elevated,the antioxidant ability and selenium content in serum and tissues of stressed broilers increased significantly.Yeast-Se had higher selenium deposition, but Na₂SeO₃ had higher GSH-Px activity in serum,especially in early phase of stress.(5) According to slope ratio assay,when sodium selenite was used as reference material,selenium content of serum,kidney,liver and breast muscle as assessment indexes,the average relative bioavailability of Yeast-Se was 132.1% under normal condition,and 141.6%under stress condition.However,when activity of GSH-Px in serum and liver were taken as assessment indexes,the average relative bioavailability of Yeast-Se was 89.6%and 95.7%,respectively.Above results indicated that(1) under normal or stress conditions,the high level of selenium improved performance,significantly increased antioxidant ability and selenium content in tissues of broiler chickens.Selenium sources significantly affected selenium content in tissue and Yeast-Se had more selenium deposition,but there was no difference in antioxidant ability in the body.(2) Yeast-Se had higher relative bioavailability value for tissue selenium content,but lower for GSH-Px activity than Na₂SeO₃.However,under stress condition,the bioavalability of Yeast-Se was higher than normal condition.