Lead Toxicity in Mute Swans

considered when using protoporphyrin to measure lead exposure in Mute
swans.
In the swans sampled during the night, little variation was
recorded in the blood parameters and all remained within the reference
range, with the exception of sodium.
The sodium values in the birds
sampled during the night were the highest recorded in this study.
Though the exact reasons for the change in sodium levels are not known,
it is suggested that stress due to caging and/or abnormal conditions
were responsible for the change.
The only other two parameters to show
noticeable changes in caged swans were urate and cholesterol.
This was
not unexpected, in that the birds did not feed very much during the
period, and urate is the breakdown product of protein (Sturkie, 1965).
Protein levels did not vary during the study, the lower urate levels
were presumably due to the slowing down of the digestive process.
While food was freely available to the birds, they were not seen to
feed and this may explain the increase in circulating plasma
cholesterol as the birds mobilised lipid to maintain body functions.
The level of protoporphyrin IX was high for six cygnets (less than
4 months old) and all values were above the upper reference range and
the values set the maximum level recorded for the normal swans (Table
4). While the exact reason for this is unknown, Lucas and Jamroz,
(1961) reported occasional early developmental stages of red blood
cells in the blood of chickens. Similarly, Smith and Engelbert (1969),
reported peripheral erythropoiesis in the blood due to mother cells
releasing 'clone' cells which are relativeley undifferentiated,
immature red blood cells. The frequency of such 'clone' cells in the
peripheral blood of young hatched chicks averages 5.2 percent (Smith
and Engelbert, 1969).
The values obtained from the young birds in this
study are probably due to the presence of a proportion of red blood
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