Effects of different dl‐selenomethionine and sodium selenite levels on growth performance, immune functions and serum thyroid hormones concentrations in broilers

Abstract

This trial was conducted in a 2×3+1 factorial arrangement based on a completely randomized design to evaluate the effects of different dl-selenomethionine (dl-Se-Met) and sodium selenite (SS) levels on growth performance, immune functions and serum thyroid hormones concentrations in broilers. A total of 840 Ross 308 broilers (7days old) were allocated by body weight to seven treatments (three replicates of 40 birds each treatment) including (1) basal diet (containing 0.04mg of selenium (Se)/kg; control) without supplementary Se; (2, 3 and 4) basal diet+0.05, 0.15 or 0.25mg/kg Se as SS; (5, 6 and 7) basal diet+0.05, 0.15 or 0.25mg/kg Se as dl-Se-Met. The experiment lasted 42days. The results revealed that dietary Se supplementation improved (p<0.05) average daily gain, feed efficiency, immune organ index, serum immunoglobulin A (IgA), immunoglobulin G (IgG), immunoglobulin M (IgM) and triiodothyronine (T3 ) concentrations and decreased (p<0.01) thyroxine (T4 )/T3 ratio in serum compared with the control. Broilers receiving the dl-Se-Met-supplemented diets had higher (p<0.05) feed efficiency, thymus index, the amounts of IgA, IgG, IgM and T3 as well as lower (p<0.05) serum T4 concentrations and T4 /T3 ratio than those consuming the SS-supplemented diets. Serum IgA and IgM levels of broilers fed 0.15mg Se/kg were significantly higher (p<0.05) than those of broilers fed 0.05 or 0.25mg Se/kg. In summary, we concluded that dl-Se-Met is more effective than SS in increasing immunity and promoting conversion of T4 to T3 , thus providing an effective way to improve the growth performance of broilers. Besides, based on a consideration of all experiment indices, 0.15mg Se/kg was suggested to be the optimal level of Se supplementation under the conditions of this study.