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OCR for page 1
Introduction
All mineral elements, whether essential or nonessential, can adversely
affect an animal if included in the diet at excessively high levels. Un-
doubtedly, tolerance levels vary from animal to animal and even from
day to day in a single animal. Many factors, such as age and physiologi-
cal status of the animal (growth, lactation, etc.), nutritional status,
levels of various dietary components, duration and route of exposure,
and biological availability of the compound, influence the level at which
a mineral element causes an adverse effect.
There are several reasons for concern about the possibility of exces-
sive mineral intake by animals. The levels of some minerals in plant
tissues vary greatly due to soil factors and the quantity and availability
of the mineral present in the soil. Manganese, selenium, and molybJe-
num, for example, may occur in forages at such elevated levels that,
when consumed, result in adverse effects on the animal. The leaves and
stems of forages can also become contaminated with minerals such as
cadmium, lead, or fluorine from industrial-processing plants, resulting
in amounts of the contaminating element sufficient to cause harm to
animals consuming the forage. Natural water supplies may contain
excessive levels of sulfur, fluorine, sodium, magnesium, or iron. In
addition, some minerals may be contributed to the water by industrial
wastes and other sources of pollution. Mineral supplements are pro-
vided frequently to correct the deficiencies in diets formulated from
natural feedstuffs. These supplements contain variable amounts of ele-
ments other than those of primary interest. The amounts of "other"
OCR for page 2
2
Introduction
elements depend on the native material from which the mineral supple-
ment is obtained and the type of processing that it undergoes.
Increased recycling of animal wastes results in higher mineral intakes
by animals. As animals digest and utilize the nutrients in their diet,
there is a proportionately greater disappearance of organic nutrients
with a consequent increase in the concentration of mineral elements in
the excrement. In addition, some by-product feedstuffs, such as the
residue remaining from the fermentation of molasses, may have high
levels of minerals.
The accidental administration of excessively high levels of minerals
is another reason for concern about the effect of excess minerals in
domestic animals. Such administration can result in acute signs of
toxicosis, which may be quite different from the chronic effects dis-
played after minerals have been fed at higher than normal levels over
an extended period of time.
The words "mineral" or "minerals" as used in this publication refer
to the elements rather than to an ore of geologic origin.
Representative terms from entire chapter:
nutritional status
