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human diseases and in toxicity tests. In addition, animals
are used as an asset to teaching health professionals and
training their surgical skills.
7
Investigators should know the particular traits of the
species they intend to use, such as its physiology, devel-
opmental stages, reproductive characteristics, specific
behaviors and nutritional needs. In practice, when actu-
ally conducting experiments, choosing the appropriate
animal model is done based on how easy the husbandry
practices and handling of the animal species are, rather
than experimental design or animal biological relevance.
8
Rodents, especially rats and mice, are among the most
commonly used animals in scientific research.
3
In the
United States alone, 26 million mice and rats are used per
year, which makes up to 96 to 98% of all animal testing.
9
Rats are most appropriate for work involving shock,
sepsis, obesity, peritonitis, cancer, gastric ulcers, intestinal
operations, the mononuclear phagocytic system, spleen,
wound healing and organ transplantations (Figure 1).
Mice, in turn, are more suited to studying megacolon and
burns, as well as shock, sepsis, obesity and cancer, as pre-
viously mentioned.
3
Pigs are used in liver, stomach and transplantation
studies (Figure 2), whereas rabbits are suited for studies
on immunology, shock, inflammation, colitis, vascular
operations and transplantations. Dogs fell into disuse,
mainly due to the activity of NGOs engaged in protecting
the species. However, their use was common in teaching
surgical technique and studying shock, malabsorption,
colitis, pancreatitis, hepatic and splenic operations, as
well as transplantations.
3
Thus, choosing an animal for laboratory use depends
on the scientific research. There are some animals whose
genetic lineage makes them prone to certain diseases, such
as diabetes mellitus or high blood pressure, and therefore
are ideal choices for testing drugs and/or procedures when
studying such conditions.
9
It is of utmost importance to know the microbio-
logical standard of laboratory animals, given that it not
only affects people, but can also influence the results of
the experiments. Studies have been using an increasing
number of specific pathogen-free (SPF) animals, that is,
animals which are free of specific microorganisms and
parasites. In order to obtain this type of sanitary status,
it is essential that animals be husbanded and kept in
settings that are protected by strict sanitary barriers
and frequently monitored, since many rodent infections
are subclinical.
10
H
ousing
and
environmental
enrichment
Several aspects relative to the husbandry and housing of
species are neglected. Group housing is important, but
can give rise to aggression, hence causing pain, injury or
death. Also, animals that are stressed or injured may com-
promise the scientific validity of the study.
11
Investigators should be concerned about the circum-
stances in which animals are kept during the study, as well
as familiarize themselves with the metabolism of the species
kept in vivaria, which can be altered by factors such as
confinement, stress, pain, lack of sunlight and more.
8,12
Housing conditions not only affect the behavior of the
animals but also interfere with the results of the experiments.
Environmental enrichment and enhancement procedures
help reduce stress and positively affect performance.
6
Accordingly, knowledge of the specific behavior and
physiology of the species is extremely important, so that
FIGURE 1
Healing test using rats as an animal model.
FIGURE 2
Operative technique using pigs as an animal model.