Biomedical Engineering Reference
In-Depth Information
from the group and allows the caretaker to know both what
to offer the separated animal as well as how much food to
subtract from that given to the remaining group members.
This is especially true for the enrichment portion of the
diet, as otherwise removing an animal from the group
would in effect likely increase one or more of the remaining
animals' intake of enrichment foods, potentially diluting
their nutrient intake.
The most important aspect of group feeding is moni-
toring animal interactions and the body weight of each
individual. Body weight is a good indication of nutritional
health. For the purpose of diet management animals should
be weighed monthly. The diet needs to be modified as the
animals move through different life stages and as indicated
by changes in body weight. Caretakers and researchers
need to evaluate each animal as an individual and deter-
mine the best body weight range for the individual.
Although for some species there are published general body
weight ranges, individuals will vary and accurately evalu-
ating each animal and establishing an individual normal
weight range is invaluable.
fed at 80
e
90% of the total diet, and thus have a built-in
safety margin based on the expectation that supplemental
foods of unknown nutritional quality will also be offered.
Choosing Appropriate Nutrient Levels
It is critical to supply an animal with the appropriate level
of nutrients for its particular life stage, activity level, and
performance criteria (e.g. participating in a study vs.
maintenance animal, diseased vs healthy, etc.) without
causing deficiency or toxicity. With all nutrients, there is
a concentration range which will meet the needs of the
animal and provide a margin of safety in case of nutrient
loss due to long-term diet storage, improper handling/
storage of diet items, higher than normal nutrient needs
(e.g. reproduction), or some other condition resulting in
a need for higher nutrient levels. However, for many
nutrients, toxicity can be a significant concern. As
mentioned previously, the vitamins of greatest concern for
toxicity are the fat-soluble vitamins (A, D, E, and K) for
which excretion is much more difficult than for the water-
soluble vitamins (B vitamins, vitamin C). In regards to
minerals, selenium is likely the most toxic, but all minerals
can be toxic in excess (
National Research Council, 2005
).
An additional consideration is not just the level of
a particular nutrient, but the source of that nutrient and its
availability to the animal. For example, in the case of
minerals, inorganic sources such as sulfates are often the
traditional dietary source, but more stable, covalently
bound minerals such as hydroxy minerals or chelated
minerals may be incorporated into manufactured feeds.
These mineral sources tend to be more stable in the diet and
more bioavailable to the animal, although this varies
depending on the mineral and the chelate (
National
Research Council, 2005
).
When examining commercially manufactured feeds,
there is a minimum amount of information that must be
provided by the manufacturer, including minimum crude
protein and fat levels and maximum fiber levels. High
moisture diets such as canned foods will also provide
a maximum guaranteed moisture level. Keep in mind that
these are simply minimum or maximum levels and do not
necessarily reflect the precise amount of a nutrient in the
feed. Most manufacturers will provide other pertinent
information regarding essential nutrients in their feeds so
that the feed can be evaluated in relation to nutrient
requirements of the species being fed.
Commercially manufactured dry diets are generally
designed to be stored in dark, dry conditions of
Purposes of Manufactured Feeds
A manufactured feed may be designed to be complete or to
provide supplementation or enrichment. A complete feed is
“a nutritionally adequate feed for animals that is com-
pounded to be fed as the sole ration and is capable of
maintaining life and/or promoting production without any
additional substance being consumed except water”
(
Association of American Feed Control Officials, 2008
). In
contrast, a supplement is “a feed used with another to
improve the nutritive balance of performance of the total”
(
Association of American Feed Control Officials, 2008
).
A supplement may also be used to provide enrichment
or training rewards to the animal. For example, a diet
component that promotes natural foraging behavior may be
used for enrichment or a preferred supplement may be used
as a positive reinforcement tool during animal training.
Additional benefits would be for these foods to be easy to
store and feed out and to be inexpensive.
In order to ensure that proper nutrition is achieved, it is
critical to understand how the diet components provided to
animals fit into this continuum. For instance, if a diet
designed to be a complete feed is only offered at 50% of the
total diet, with supplemental food items comprising the
remainder of the diet, the nutrients in the complete feed
might be “diluted” by components of the supplements,
which often are high moisture and/or high sugar items that
are low in nutritive value (e.g. fresh fruits). It is important to
understand how the manufactured complete feed was
designed to be fed in order to provide supplemental food
items in appropriate amounts. For example, diets formu-
lated for laboratory animals generally are designed to be
50%
<
75
F. Cold storage can potentially
increase the shelf life of the diet, but the humidity needs to
be controlled carefully; a cold environment with high
moisture can result in mold growth. In appropriate storage
conditions, the manufacturer's shelf life or use-by date will
relative humidity and
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