Comparative effects of inorganic and organic dietary sources of selenium on selenium levels and selenium-dependent glutathione peroxidase activity in blood of young turkeys.

The effect of various dietary sources of Se on Se-dependent glutathione peroxidase (SeGSH-Px) activity in plasma and whole blood was studied in turkeys. Day-old poults were fed low Se diets (supplemented with vitamin E) for 15 to 24 days before being fed experimental diets for 7 to 10 days. Menhaden fish meal (0.1 ppm Se) increased plasma SeGSH-Px activity by 45% of the response to 0.1 ppm Se as Na2SeO3. Poults supplemented with 0, 0.1, 0.2, or 0.4 ppm Se as Na2SeO3, had similar increases in plasma and whole blood Se levels; however, SeGSH-Px activity of plasma (r = 0.96) was better correlated with dietary Se than that of whole blood (r = 0.64). The supplement of 0.4 ppm Se increased the activity of SeGSH-PX almost 20 times in plasma but only 1.6 times in whole blood. The effectiveness of several compounds providing 0.2 ppm Se for increasing plasma SeGSH-Px activity was: Na2SeO4 greater than SE-DL-cystine greater than Se-DL-methionine and Se-DL-ethionine. The effect of Na2SeO3 was not significantly different from that of Se-DL-cystine, Se-DL-methionine or Se-DL-ethionine. The ratio of SeGSH-Px activity:Se concentration, indicating the amount of Se associated with enzyme activity, was highest in plasma of poults fed Na2SeO4 and Se-DL-cystine. The data demonstrate differences in the availability of various Se sources for SeGSH-Px activity of poults.