Lead Toxicity in Mute Swans

DISCUSSION
The normal range of haemoglobin, mean cell haemoglobin
concentration and haematocrit values reported here for Mute swans
(Table 1) do not differ greatly from those reported elsewhere for other
species of birds (Hodges, 1977) or mammals (Eccleston, 1977).
Methodological deficiencies in the estimation of haemoglobin
concentration have however resulted in a great deal of variation in
reported values (Hodges, 1977).
What is noticeable is the variation in
the degree of sensitivity of different tests. Haematocrit has such a
large reference range and is a crude method for the assessment of
health or the effects of disease.
This is further shown by the fact
that no detectable differences were found in haematocrit values for age
and sex.
This may explain why Custer et al., (1984) found no
difference in the haematocrit values of American kestrels Falco
sparversus (L) which were exposed to high lead.
On this basis, the use
of haematocrit without knowledge of haemoglobin level as a measure of
health or as measure of change in sick birds must be treated with
caution.
The level of haemoglobin was less variable and significant
differences were found (Table 1).
However, any differences between
sexes should be viewed with caution, since.levels of haemoglobin varied
greatly between individuals. While there were apparent differences on
the gross scale, these differences may not be significant in individual
birds.
This can be seen from the large overlap in the reference
distributions for the different classes (Table 1). Values of mean cell
haemoglobin, provide a very useful measure of haemoglobin status and no
differences were found between sexes.
In most mammals and birds a MCHC
value of less than 30.00 g/lOOmls is considered abnormal, (C. Hawkey
pers. comm.).
- 102 -
I