THE BIOAVAILABILITY OF VARIOUS SELENIUM-COMPOUNDS TO A MARINE WADING BIRD

The uptake of dietary selenium (about 3.5 mg/kg AF dry wt) as selenome thionine, selenocystine, selenite, selenate, and fish selenium in the plasma and red blood cells (RBC) of the oystercatcher has been investi gated. The birds received the various selenium compounds subsequently, for at least 9 wk. After dietary supplementation of selenocystine, se lenite, and selenate, plasma selenium was about 350 mu g/L and RBC sel enium 2.1 mg/kg dry wt. After supplementation of selenomethionine, the plasma concentration increased to 630 mu g/L, and the RBC concentrati on to 4.1 mg/kg dry wt. When the fodder contained 3.1 mg/kg fish Se, a n average plasma and RBC concentration of 415 mu g/L and 14.4 mg/kg dr y wt, respectively, was measured. The maximal increase of the selenium concentration in the plasma was attained at first sampling, 14 d afte r a change in dietary selenium (selenomethione or fish Se); the uptake seemed to be a concentration-regulated process. RBC concentrations (Y in mg/kg dry wt) increased with time (X in d) according to Y = a - b e-(cX) Fifty percent of the total increase was attained within 17 d, s uggesting that diffusion into the RBC played a role. The selenium conc entration in the plasma was positively correlated with the (fish)Se co ncentration in the fodder; the RBC concentration (60 d after the chang e in diet) was positively correlated with the plasma concentration. Wh en the diet contained fish Se, the blood selenium concentrations of th e captive birds were similar to the concentrations measured in field b irds. Fish Se is a yet undetermined selenium compound. The present exp eriment showed that fish Se differed from selenomethionine, selenocyst ine, selenite, or selenate in uptake from the food and uptake in the R BC.