Biomedical Engineering Reference
In-Depth Information
undesired behavior may transiently decrease upon initial
presentation of the device (
Lutz et al., 2003
). However,
once the foraging opportunity is gone, the animal often
returns to performing the behavior (
Lutz and Farrow, 1996
).
Other enrichment strategies are more effective in reducing
undesired behaviors over
(
de Waal, 1991
), and as such is one of the best overall
enrichment options for most captive NHPs (
Crockett, 1990;
de Waal, 1991; Lutz and Novak, 2005
). However, of the
different types of enrichment, social enrichment requires
the greatest amount of attention to the differences among
NHP species and the greatest expertise in understanding
behavior by those working with primates.
Social housing increases the opportunity for animals to
engage in many species-typical behaviors, including play,
feeding, and grooming (
Schapiro et al., 1996a
). It can
reduce abnormal behaviors such as stereotypic behavior
and self-injurious behavior (
Schapiro et al., 1996a; Weed
et al., 2003
). Importantly, social enrichment, particularly
early in life, is also an effective tool for the prevention of
abnormal behaviors. As mentioned above, some of the
primary risk factors for developing self-injurious and other
abnormal behaviors in macaques involve being reared
without appropriate close social contact with conspecifics
and living in single housing for extended periods when
young (
Bellanca and Crockett, 2002; Novak, 2003;
Rommeck et al., 2009a,b
). In addition, the presence of
familiar companions can mitigate the effects of various
stressors and alter immune function, which can improve
well-being (
Schapiro et al., 2000; Gilbert and Baker, 2011
).
Taken together, social enrichment is one of the most
important parts of an effective behavioral management
plan.
The importance of social housing is reflected by Euro-
pean and US regulatory agencies, which require social
housing for captive NHPs. The 2011 revision to the Guide
unambiguously states that single housing for social animals
should be the exception, acceptable only in situations in
which there is either a behavioral or veterinary concern
(e.g. the animal may cause harm to itself or others) or an
experimental requirement approved by the IACUC
(
National Research Council, 2011
). Importantly, the Guide
also states that IACUC approval for such research-
protocol-related social housing exemptions should be based
on currently accepted standards. Thus, as refinements are
developed that allow social housing of experimental
animals, IACUC approval for single housing should
diminish. When animals are singly caged, they may require
more cage space than is required for pair- or group-housed
primates, as well as the provision of additional enrichment
such as increased human contact, or periodic use of activity
cages (
National Research Council, 2011
). The need for
single housing should be reviewed by the attending veter-
inarian and IACUC on a regular basis (
National Research
Council, 2011
).
Options for social housing can vary from indoor cages
housing a pair of animals (i.e. pair housing) to large,
outdoor enclosures containing many animals. Ideally,
primates should be kept in housing that provides for
expression of their natural behavior. Unlike many other
time. Benefits of
specific
enrichment are addressed below.
The decision to utilize particular behavioral manage-
ment strategies should, whenever possible, be based on the
scientific literature (
National Research Council, 1998
).
There has been a tremendous increase in the number of
publications that evaluate the effects of enrichment for
nonhuman primates. Peer-reviewed studies of behavioral
management strategies for primates are routinely published
in many journals serving the biomedical research
community as well as in primate-specialty journals.
However, studies have mainly focused on assessing the
behavioral effects of behavioral management procedures,
with much less attention paid to the influence of these
procedures on dependent measures relevant to biomedical
research studies (but see
Schapiro et al., 2000
for an
exception). Since studies in rodents have shown that
enrichment can cause neurological changes, including
increased brain size and weight (
Greenough, 1975
),
increased numbers of synapses per neuron (
Benefiel and
Greenough, 1998
), and increased neurogenesis (
Kemper-
mann et al., 1997
), enrichment itself could be a potential
variable in studies (
Bayne, 2005; Hubrecht, 2010
). There is
a strong need for additional research that attempts to
document the impact of behavioral management proce-
dures on primates used in biomedical research.
Because enrichment can affect physiological variables
in NHPs, it is important that scientific staff be familiar with
the environmental enhancement plans approved for their
facility. Further, investigators need to be aware of any
research protocol restrictions that may require exemptions
from the behavioral management plan and report these to
the Institutional Animal Care and Use Committee
(IACUC). The process employed at one National Primate
Research Center is described in detail by Thom and
Crockett (
Thom and Crockett, 2008
).
Examples of Enrichment
Social Enrichment
Most species of nonhuman primates are social and have
evolved to live in complex societies. They form intricate
social relationships in the wild, spending a great deal of
time engaged in social behaviors, including grooming and
huddling with other members of the troop. Providing social
housing for NHPs affords them the opportunity to engage in
species-specific social behaviors and to develop many of
the cognitive and social skills necessary for group living
