B. OTHER ENVIRONMENTAL FACTORS 1. Noise
The effects of noise on laboratory animals are related to its intensity, frequency, rapidity of onset,
duration and characteristics of the animal (species, strain, noise exposure history). Species differ in their auditory sensitivity and susceptibility to noise-induced hearing loss. Prolonged exposure to high levels of noise can cause auditory lesions in animals. Although a maximum background noise of 85 db has been recommended (Baker, 1979), adverse changes have occurred in rats exposed to intermittent noise at 83 db (Gerber, Anderson and Van Dyne, 1966). Exposure to uniform stimulus patterns may lead more readily to hearing loss, whereas exposure to irregular patterns may be more likely to cause disorders due to repeated activation of the neuroendocrine system (Peterson, 1980).
Intense noise can cause alterations in gastrointestinal, immunological, reproductive, nervous, and
cardiovascular systems, as well as changes in development, hormone levels, adrenal structure, blood cell counts, metabolism, organ weights, food intake, and behaviour (Agnes, Sartorelli, Abdi et al. 1990;
Bailey, Stephens and Delaney, 1986; Fletcher, 1976; Kraicer, Beraud and Lywood, 1977; Nayfield and Besch, 1981; Pfaff, 1974; Gerber and Anderson, 1967). Sudden intense sound can elicit startle responses and can precipitate epileptiform seizures in several species and strains of laboratory animals (Iturrian, 1971; Pfaff, 1974). Ultrasound emissions can cause behavioural disturbances in a variety of species (Algers, 1984). Although firm criteria for noise tolerance have not been established for laboratory animals as for humans (Falk, 1973; Welch and Welch, 1970), unnecessary and excessive noise may be assumed to be an important experimental variable and a possible health hazard.
Noise can be controlled in an animal facility through proper facility design and construction, thoughtful selection of equipment, and good management practices. Naturally noisy animals should be located where they minimally disturb quiet, noise-sensitive species. Fire alarms which operate at low frequencies are audible to humans, but do not disturb mice and rats. Telephones should not be placed in animal rooms. Many noise sources in an animal facility emit ultrasound (Sales, Wilson, Spencer et al. 1988).
These include running taps and squeaking chairs. Efforts should be made to identify and correct or shield these sources.
Noise can also disturb or harm animal care staff, researchers, and other nearby personnel. It may be necessary to provide ear protectors in some areas such as dog, pig, or monkey rooms, or the cage-washing facility.
Chemicals in the environment can adversely affect the laboratory animal in a variety of ways. Inherently toxic compounds or toxic metabolites can have local and/or systemic effects on virtually every system.
Although most chemicals found in animal facilities exert their major effect by altering hepatic microsomal enzyme activity, immune function, or behaviour, allergens, mutagens, teratogens, and carcinogens have also been detected. Their ultimate effect is modulated by the interplay between chemical factors
(concentration; physicochemical properties; duration, frequency, and route of exposure; interaction with other agents) and host factors (species, age, sex, strain, nutritional status, immune function, disease status) (Baker, Lindsey and Weisbroth, 1979).
Chemicals arrive in the microenvironment through air, water, food, bedding, and contact surfaces.
Common air pollutants include dust and bedding particles, ammonia, disinfectants, pheromones, organic solvents, volatile anesthetics, insecticides, and perfumes or deodorants.
The most common air contaminant in animal facilities is ammonia (NH3) resulting from the decomposition of nitrogenous waste. Ammonia causes irritation of the respiratory epithelium and increases susceptibility of rodents to respiratory mycoplasmosis (Broderson, Lindsey and Crawford, 1976; Lindsey, Connor and Baker, 1978). Sub-clinical pathological changes in the respiratory tract due to ammonia complicate inhalation toxicity studies in laboratory rodents (Gamble, 1976). In humans, 25 ppm is the level below which there are no harmful effects from an 8 hr/day, 5 day/week exposure [American Conference of Government and Industrial Hygienists Threshold Limit Value (TLV)]. The human odour detection threshold for ammonia is 8 ppm. In comparison, the TLV is 17 mg/m3.
The animal's microenvironment must be checked as well as the room, because conditions often differ significantly between the two (Corning and Lipman, 1992). Ammonia levels build up when production components (species, sex, housing density, bedding) exceed elimination components (cage design, air exchange, frequency of cleaning) (Serrano, 1971). Filter covers, which reduce air exchange at the cage level, can rapidly lead to detrimental concentrations of NH3. Controlling NH3 within safe levels requires constant attention to stocking density and to frequency of cage cleaning.
Perfume and deodorants should never be used to mask ammonia or other animal odours in lieu of proper husbandry. These substances may be harmful to the animals (Baker, Lindsey and Weisbroth, 1979;
Pakes, Lu and Meunier, 1984). Volatile anesthetics should be used only with proper scavenging equipment.
Chemicals can enter the animal's environment through the water. Other than checking for bacterial contaminants, water quality is rarely monitored except for aquatic animals. Chlorinated municipal water sources are commonly used. Over 700 organic compounds have been isolated from such sources - 90%
are natural decomposition products. These may react with chlorine to produce chloroform (Pakes, Lu and Meunier, 1984). Inorganic solutes, particularly copper (from copper pipe) and chlorine are especially hazardous to aquatic organisms.
Food may be contaminated with heavy metals (e.g., lead, arsenic, cadmium, nickel, mercury), naturally occurring toxins (e.g., mycotoxins, ergot alkaloids, pyrrolizidine alkaloids, estrogenic compounds), agricultural chemicals (e.g., herbicides, pesticides, fertilizers), and additives (e.g., antibiotics, colouring, preservatives, flavourings, unintentionally incorporated drugs) (Baker, Lindsey and Weisbroth, 1979;
Pakes, Lu and Meunier, 1984; Silverman and Adams, 1983).
Chemicals found on contact surfaces include cleaning agents such as soaps, wetting agents, detergents, solvents, and disinfectants (Burek and Schwetz, 1980). Unless otherwise specified as safe according to the manufacturer's instructions, these substances should be thoroughly rinsed from surfaces which will contact animals. The efficacy of the rinse cycle of the cage-washer should be checked periodically.
Bedding materials, particularly wood products, may introduce naturally occurring volatile oils, herbicides, pesticides, and preservatives into the animal's microenvironment. Other possible contaminants include PCB's and antibiotics (Silverman and Adams, 1983). Volatile hydrocarbons in cedar and pine shavings can induce hepatic microsomal enzymes (Weisbroth, 1979).
The choice of bedding materials and cage flooring profoundly affects the microenvironment of small rodents. In most circumstances, contact bedding is recommended. Most species should be provided with solid flooring and bedding prior to parturition. Some desirable characteristics of contact bedding are listed below.
Bedding material should always be taken into consideration in designing an experiment and should be uniform throughout the study because of its influence on behavioural and physiological responses and on toxicity and carcinogenesis studies.
DESIRABLE CRITERIA FOR RODENT CONTACT BEDDING (Kraft, 1980)
Unable to support bacterial growth
Deleterious products not formed as a result of sterilization
Non-desiccating to the animal
Unlikely to be chewed or mouthed
Disposable by incineration
Remains chemically stable during use
Manifests batch to batch uniformity
Optimizes normal animal behaviour
Non-deleterious to cage-washers
Non-injurious and non-hazardous to personnel
Unsterilized materials are a possible source for the introduction of disease into rodent colonies. Wild rodents enjoy nesting in packages of bedding, and cats will defecate in loose bedding (Newman and Kowalski, 1973). Recommended bedding materials for each species are discussed in Volume 2 of this Guide.
4. Population Density and Space Limitations
Population density and group size influence the physiological and psychological state of the animal and can profoundly affect experimental responses (Baer, 1971; Clough, 1976). Productivity, growth, and behaviour of laboratory mice may be seriously altered by variations in floor space alone. Infant growth and survival, as well as maternal behaviour, may be adversely affected by excessive floor space. Infant mortality in large cages can occur from failure of females to nurse their young due to inhibition of
mammary development. Nest-building behaviour in rats is adversely affected in densely populated pens, leading to an increasing tendency to ignore the pups and to infant death. Housing density can affect efficiency of feed utilization and the incidence of skin lesions (Les, 1968, 1972).
Isolation stress may result in increases in nervousness, aggression, susceptibility to convulsions and certain drugs, metabolism, and adrenocortical activity (Balazs and Dairman, 1967; Hatch, Weiberg, Zawidzka et al. 1965; Moore, 1968). As much as possible, housing type and densities should be kept uniform throughout a study. Further details on appropriate housing (see also Laboratory Animal
Facilities). Individual species requirements are discussed in Volume 2 of this Guide (see also Social and Behavioural Requirements of Experimental Animals). Recommended housing densities are listed in Appendix I.