Biomedical Engineering Reference
In-Depth Information
C (e.g. L-ascorbyl polyphosphate) are not impacted to the
same degree (e.g.
Figure 10.1
).
Moist diets are generally produced in a similar manner
to extruded dry diets but using high-moisture ingredients.
These diets are typically sealed in cans and can be
a component of primate diets. Gel diets are also high-
moisture diets, but are often sold as a dry meal, to which the
end-user adds water and creates a moist diet. Gel diets offer
options for providing medications under veterinary care, as
well as other additives. Care must be taken to account for
temperature sensitivity of additives as well as proper
inclusion rates. High-moisture diet items may necessitate
cold storage and have an increased risk of bacterial or
fungal growth compared to dry diets if not stored properly
and under manufacturer's suggested conditions.
In order to compare diets manufactured under different
conditions, it is important to examine their nutrient content
on a dry matter basis (i.e. no moisture). For example, when
comparing the protein level of an extruded biscuit versus
a canned diet, an extruded biscuit containing 20% crude
protein and approximately 10% moisture would contain
~ 22.2% protein on a dry matter basis. The canned diet
containing 8.5% crude protein and ~ 60% moisture would
contain ~ 21.3% protein on a dry matter basis. This type of
calculation will allow a comparison between diets (as well
as supplemental food items) to be completed accurately. If
possible, calculating nutrients on a per energy basis will
also allow direct comparisons between diets.
Finally, the physical form should match the masticatory
capabilities of the species and individuals in question. Many
of the small primates (e.g. squirrel monkeys, marmosets,
and tamarins) may have difficulty with hard pellets or
extruded biscuits. Geriatric animals or animals with tooth
problems may also not do as well with hard foods.
FIGURE 10.3
Effect of autoclave temperature and time on thiamin
and vitamin A in extruded diets. Data represents duplicate assays for
vitamins. Autoclave conditions consisted of 15 lb pressure at indicated
times and temperatures. (Data from Purina Mills
internal research.)
(
Hanis et al., 1988
). The dose of irradiation affects the level
of microbial survival as well as the retention of nutrients.
For example, irradiation of cereal meals at 1 kGy had little
effect on thiamin retention, but irradiation at 10 kGy
reduced thiamin to 67
e
85% of original values and irradi-
ation at 25 kGy reduced thiamin to 42
e
75% of original
values (
Hanis et al., 1988
). Vitamin losses in complete
feeds tend to be lower, most likely due to the increased
complexity of the feed as well as presence of antioxidants
(
Aziz et al., 2006
). No meaningful changes in amino acid
availability were noted with irradiated diets (
Leeson and
Marcotte, 1993
), while the effect of irradiation on lipid
sources depends on the type of diet. Semi-purified diets
with high unsaturated fatty acid content may be susceptible
to lipid peroxidation as a result of irradiation, however diets
prepared with traditional ingredients and/or lower fat levels
are not affected by irradiation (
Leeson and Marcotte, 1993
).
Irradiation of feeds has not been shown to result in any
altered metabolism, reproductive success, or growth rates
of four successive generations of rats (
Read et al., 1961
).
Special Diet Processing Considerations
Although not common for primate diets, many laboratory
diets for other species are autoclaved or irradiated to
provide sanitary feed for pathogen-free or germ-free
animals. Autoclaving subjects the diet to high pressure
steam at 121
C or more for a time period of at least
15 minutes. Autoclaving is associated with some nutrient
losses, so those nutrients must be over-fortified in the diet
prior to autoclaving. For example, autoclaving is associated
with 40
e
60% loss of vitamin A (
Maerki et al., 1989
), as
well as some decreases of amino acid availability (
Ford,
1976
). It is important to keep in mind that the length of time
and temperature at which a diet is autoclaved will affect the
degree of vitamin loss (
Figure 10.3
).
Irradiation is a process where feed is exposed to
ionizing radiation, which causes chemical changes that
destroy DNA and reduce microbial contamination of feeds
REFERENCES
Association of American Feed Control Officials (AAFCO). (2008). Offi-
cial Publication.
<
http://www.aafco.org/Publications/tabid/75/
Default.aspx
>
Accessed 08.19.11.
Ausman, L. M., & Hayes, K. C. (1974). Vitamin E deficiency anemia in
old and new world monkeys. Am. J. Clin. Nutr., 27, 1141
e
1151.
Aziz, N. H., Souzan, R. M., & Azza, A. S. (2006). Effect of gamma
irradiation on the occurrence of pathogenic microorganisms and
nutritive value of four principal cereal grains. Appl. Radiat. Isot., 64,
1555
e
1562.
