Second North American Sea Duck Conference - Patuxent Wildlife ...

SECOND NORTH AMERICAN SEA DUCK CONFERENCE
EFFECTS OF DIETARY SELENIUM EXPOSURE IN
CAPTIVE AMERICAN COMMON EIDERS
J. Christian Franson¹, David J. Hoffman², Alicia M. Wells-Berlin 2 , Matthew C. Perry², Valerie S.
Bochsler 1 , Daniel L. Finley1, Paul L. Flint 3 , andTuula Hollmén 4
¹USGS National Wildlife Health Center, Madison, Wisconsin, USA; chris_franson@usgs.gov
²USGS Patuxent Wildlife Research Center, Laurel, Maryland, USA;
³USGS Alaska Science Center, Anchorage, Alaska, USA;
4 Alaska Sealife Center and School of Fisheries and Ocean Sciences, University of Alaska Fairbanks,
Seward, Alaska, USA
We conducted two studies of Se exposure in captive common eiders (Somateria mollissima). In
Study 1, eiders were fed diets with added Se (as L-selenomethionine) in concentrations increasing
from 10 ppm to 80 ppm. In Study 2, eiders received control, low exposure (20 ppm Se), and high
exposure (60 ppm Se) diets. One duck in the high exposure group in Study 2 died after 36 days.
Remaining high exposure ducks in Study 2 and ducks in Study 1 were euthanized after losing 25-
30% of their body weight, which occurred after 41 days and 60-78 days, respectively. Body weights
did not differ between control and low exposure ducks in Study 2. At the end of Study 1, the mean
Se concentration in blood was 32 ppm wet weight (ww). In Study 2, mean blood Se reached 14 ppm
ww in the low exposure group and 17 ppm ww in high exposure ducks. Mean Se concentrations in
liver were 1252 ppm dry weight (dw) in Study 1, and 351 and 735 ppm dw, respectively, in the low
and high exposure groups of Study 2. Oxidative stress was evidenced by Se-associated effects on
glutathione metabolism, but not entirely in the same manner as with previous laboratory studies in
mallards. In plasma, activities of total and Se-dependent glutathione peroxidase increased with time.
As Se concentrations in liver increased, Se-dependent glutathione peroxidase, glutathione reductase,
oxidized glutathione, and the ratio of hepatic oxidized to reduced glutathione increased. Total and
protein bound sulfhydryl concentrations, reduced glutathione, glutathione-S-transferase, and glucose-
6-phosphate dehydrogenase in liver were negatively correlated with Se concentrations in the liver. In
Study 2, spleen weights were significantly lower in ducks receiving 60 ppm Se than in those receiving
20 ppm. Gross lesions associated with high Se exposure included emaciation, absence of thymus, loss
of nails from digits, and alopecia. Microscopic lesions included severe depletion of lymphoid organs,
hepatopathy, and necrosis of feather pulp and feather epithelium. Common eiders fed high levels of Se
lost weight and developed lesions similar to findings in experimental mallards, but they accumulated
greater Se concentrations in tissues, particularly liver. Field studies have shown that apparently healthy
seaducks generally have higher levels of Se in liver than healthy fresh water birds, but lower than the
concentrations we found in our study. We conclude common eiders and probably other seaducks have
a higher threshold, or adverse effect level, of Se in tissues than fresh water species.
NOV. 7-11, 2005 ANNAPOLIS, MARYLAND, USA
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