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OCR for page 3
Maximum
Tolerable Levels
the mineral tolerances of animals have been investigated in a wide
variety of studies in which graded levels of the element were offered and
specific effects examined. Ideally, long-term feeding studies of 1 year or
more should be conducted with domestic animals, with additional
studies in laboratory animals involving two or more generations. Exten-
sive studies of this type gene~y have not been made and, depending
on He element, may not be necessary. Studies of much shorter duration
have been conducted in which the criteria included feed intake, growth
rate, biochemical or morphological lesions, mortality, and deposition of
the element in meat, milk, or eggs. Sensitive indices of adverse health
effects were not used in most studies. Highly soluble, purified forms of
the test element typically were used to identify adverse effects and to
assess their severity. The results obtained may be different when the
element is supplied as feedgrade salts or incorporated during grown
into plant and animal products used in feed.
In this publication, maximum tolerable level is defined as Hat dietary
level that, when fed for a limited period, will not impair animal perform-
ance and should not produce unsafe residues in human food derived
from the animal. The form of element, length of study, criteria for
response, and species of test animal have all been considered in devel-
aping the suggested maximum tolerable levels of dietary minerals for
domestic animals presented in Table 1. Data obtained by routes of
administration other man om1 were used when information with the of
route was lacking. Particular consideration was given to food residues
Tom cadmium, lead, and mercury.
3
OCR for page 4
4 MINERAL TOLERANCE OF DOMESTIC ANIMALS
Although tolerance values for minerals will vary with age and physi-
olog~cal condition of the animal, only one maximum tolerable level has
been listed for each species, except in a few cases where information
was considered adequate. The discussions in the chapters for individual
elements may be helpful in developing tentative levels for other species.
The available information for most of the elements is less than desired,
and it is likely that these tolerance levels Will need to be modified.
Problems that may arise when two or more elements are present at high
levels represent a virtually unexplored area.
It is in keeping with good nutntional practice to maintain the miners
intake at required levels, which generally are well below the maximum
tolerable levels. Greater sensitivity to high mined levels can be ex-
pected in animals that are young, pregnant, lactating, malnourished, or
diseased. The amounts of certain elements, such as cadmium, lead, and
mercury, should always be maintained as far below Me maximum toler-
able level as feasible to minimize the contributions to We human diet.
The maximum tolerable levels shown in Table 1 are expressed in
terms of either parts per million (ppm) or percent (~o) in the total diet.
In discussions and tables for the individual elements, intake of the
element is usually expressed either as a concentration in the total diet
(ppm or %) or as a quantity per unit of body weight. Information on the
expected dietary intakes of domestic animals as influenced by body
weight and other factors is presented in reports of the Nutrient Require-
ments Series for the various species of domestic animals published by
the National Academy of Sciences and may be helpful in making use of
the values presented in the present publication.
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Representative terms from entire chapter:
domestic animals
