Animals used in research, teaching, and testing are complex living creatures that respond to environmental parameters. Whether living in a tightly controlled internal environment or an outdoor environment subject to weather changes, animals, through their physiological and behavioral processes, will respond to various stressors in their environment (Hale 1969; Sossinka 1982; Price 1984). Even subtle changes in the living and experimental environment can lead to confounding and variable research outcomes. Although the effects of the environment may not be readily noticeable to the investigator, variations may occur, resulting in research variability and potentially erroneous conclusions (Roe 1965; Magee 1970; van der Touw et al. 1978; Chvedoff et al. 1980; Kokolus et al. 2013). Arguably, the degree to which environmental variables influence research outcomes may not be appreciated by many researchers (Vesell and Lang 1976; Clough 1982; Siegel 2011; Bustin 2014), when their focus is on controlling direct experimental variables inherent in their research. Recently, there has been renewed emphasis regarding reproducibility in animal research outcomes (Siegel 2011; Bustin 2014), whether research is conducted between different research facilities or within the same facility, and an increased emphasis on the reporting of conditions that can cause variability when animals are used in research (Kilkenny et al. 2009, 2010).
The use of animals, whether in research, teaching, or testing, is governed by regulations, policies, and guidelines (Bayne and Anderson 2015). These documents commonly describe the care and use expectations for various species and delineate the common environmental variables, such as housing requirements, sanitation, feed, water, lighting, and temperature. Animal well-being directly correlates to the appropriateness of the many environmental variables, whether physical, nutritional, or social enrichment (Yousef 1985; Curtis 1986; Baker and Lipman 2015). Environmental conditions should minimize stress, illness, mortality, injury, and behavioral problems. Controlling environmental variables (Figure 20.1), along with the provision of appropriate husbandry, is crucial for the appropriate use and well-being of animals.
When attempting to control and minimize the effect of environmental variables on laboratory animals, the design and management of the research facility is paramount (Hessler 1999). The modern research facility, with specialized housing rooms and caging systems, provides an environment where surrounding variables are minimized regardless of species, thus creating an optimal setting and preventing perturbations of the data. In contrast, natural environments commonly used for agricultural, aquatic, and traditional nonrodent species and field studies are inherently prone to variance in environmental conditions, thus producing perturbations of generated data. Additionally, natural environments are well suited for colonies of breeding animals or holding animals until needed for use. Natural environments can subject animals to weather events, such as summer heat, winter storms, and noise. The animals need to acclimate, and appropriate shelter and wind breaks may be needed to ensure animal well-being. Regardless of the type of environment, proper housing and management are essential to ensure animal well-being and the quality of research data obtained from the animals. Qualified and dedicated personnel who adhere to well-conceived operating procedures for the facility create an environment that results in high-quality animal care.
The animal’s environment consists of both the micro- and the macroenvironment. The microenvironment refers to an animal’s primary enclosure, which includes the immediate area surrounding the animal, either in an aquarium, cage, pen, or stall, and is the environment in direct contact with the animal (FASS 2010; NRC 2011). Animals are exposed to the conditions within the microenvironment, such as temperature, humidity, noise, vibration, and air composition. The physical conditions surrounding the microenvironment are defined as the macroenvironment, which is composed of the room, barn, or pasture (NRC 2011). In many situations, the microenvironment is identical to the macroenvironment due to open caging systems or natural housing environments. In contrast, the microenvironment can be substantially dissimilar to the macroenvironment due to the design of the primary enclosure. Ventilated caging systems permit different microenvironments to exist within the same macroenvironment. For example, by providing increased high-efficiency particulate air (HEPA)–filtered airflow to and from each cage, the cages on one rack could be positive pressure, relative to the macroenvironment, to prevent entry of infectious agents, and the cages on another rack could be negative pressure to prevent the escape of infectious agents. The microenvironment and macroenvironment should be appropriate for the genetic background and age of the animals and the purpose for which they are being used.
The following sections discuss some considerations of the macro- and microenvironment related to research animals.
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