Effect of monensin on response of chicks to deficient and toxic levels of dietary selenium.

Two experiments were conducted to determine if monensin affects tissue deposition of selenium (Se) and influences the response of broiler chicks to either deficient or toxic levels of this element. In the first experiment, adding Se with or without monensin to a semipurified basal diet (containing .06 mg Se/kg) significantly increased body weight, plasma thyroxine, plasma Se, liver Se, and reduced incidence of exudative diathesis. Plasma triiodothyronine was not significantly affected. There were no significant interactions between monensin and Se in any of the parameters. Monensin did not modify the Se deficiency or affect the tissue deposition of Se. In a second experiment, broiler chicks were fed diets containing levels of Se from 0 to 5 ppm with and without monensin. The higher levels of Se significantly reduced body weight, reduced feed efficiency, and increased liver deposition of Se. A significant interaction between monensin and Se was observed for hepatic selenium content. At the highest dietary Se level, chicks fed monensin deposited less Se in the liver than chicks fed no monensin. The chick apparently differs from sheep in this regard, because a marked increase in whole blood Se was reported in lambs from ewes fed diets supplemented with monensin.