complexities of whole-body metabolism. A
fairly complete picture of the dynamics of
Zn metabolism in young rats receiving
deficient to adequate diets is now available,
although the upper ranges of the homeo-
static plateau for individual tissues and the
whole animal have not been well estab-
lished. Much work yet needs to be done on
Cu, Mn and Se, particularly with respect to
the regulation of body compartments and,
especially for Se, the roles of absorption and
endogenous excretion in homeostasis. The
effects of various physiological states, other
than growth, on trace element dynamics
were not addressed in this chapter;
however, research on the affects of ageing,
gestation and lactation shows that these are
productive areas of research in trace
element dynamics. For all the elements
discussed in this chapter, the quantity of
research conducted in dynamics with rats
and humans exceeds that performed with
farm animals, but an effort was made to
include farm animal results as much as
possible. Until a greater body of knowledge
is accumulated, extrapolation of the prin-
ciples to farm animals will be necessary,
although caution is required because of
substantial differences in the metabolism of
some elements among species.180 W.T. Buckley
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