THE MERCK VETERINARY MANUAL
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Management of Laboratory Animals

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Consistently delivered quality programs of husbandry and veterinary care provide the foundation that enables valid scientific research. For proper management of research animals, the animal care and research staff must be responsible, sensitive to the animals' health and well-being, well trained in the humane care and use of laboratory animals, highly motivated, experienced, and diligent in performing their duties and responsibilities. Standard operating procedures must be established, and training and supervision provided to assure a consistently applied and uniformly high level of animal care. Within research facilities, environmental conditions must be carefully controlled so that, along with conscientiously applied programs of animal care and use, the best possible conditions for conducting research are provided. The Guide for the Care and Use of Laboratory Animals is still the primary reference for information on basic principles and standards for laboratory animal management.

Laboratory rodents that are disease- and pathogen-free and that do not possess antibodies indicative of past infection are readily available from commercial vendors. Procuring such animals from high-quality sources, transporting them in filtered shipping containers, and maintaining them in facilities with both physical and procedural barriers to the introduction of infectious agents are effective measures to prevent disease within a colony that may confound or ruin experiments.

Although there are colonies of some species of primates that are free of most agents that cause infectious disease in these species, many primates used are of feral or wild origin. For this reason, appropriate quarantine, isolation, and conditioning programs should be implemented in addition to the program followed in the importers' facilities.

Cages, pens, or runs should provide adequate space to allow for normal physiologic needs, permit postural adjustments, and meet requirements for species-specific behavior. When possible, compatible groups of social animals should be housed together. Primary enclosures should be constructed of durable materials, easily cleaned and sanitized, and designed for comfort and safety. Static microisolation (filter top) cages and more advanced individually ventilated caging systems have been used widely for rodent housing to impede cage-to-cage transmission of infectious agents. However, infection can be transmitted horizontally or vertically from parents to progeny in breeding colonies; naive mice introduced for cross-breeding and back-crossing can perpetuate infection; and experimental mice potentially can be exposed to pathogens via a contaminated environment, shared watering valves, research devices, or when taken to laboratories. Individual ventilation of cages serves to delay deterioration of the environment within the cage and maintain a more consistent and wholesome microenvironment; it also saves space in the facility and can be engineered to minimize odors, allergens, dust, and heat exhausted into the macroenvironment. A potential drawback of ventilated cages is that hairless genotypes and neonates may be prone to chilling. This risk can be reduced by providing nesting material.

Federal law in the USA requires that laboratory dogs have an opportunity to exercise regularly and have sensory contact with other dogs unless restricted by experimental or behavioral considerations. Housing for nonhuman primates must provide social and environmental enrichment to promote their psychological well-being compatible with the experimental and practical constraints of the housing situation. Successful enrichment strategies for nonhuman primates have included pair or group housing; variation in the dietary content and method of presentation; diversification of the internal cage environment with ancillary apparatus (eg, perches, swings, or ladders); provision of devices to enhance visual, auditory, or tactile stimulation; and participation in challenging, nonaversive behavioral laboratory studies. Efforts to extend and adapt environmental enrichment practices to other laboratory animal species warrant consideration and have been implemented in many institutions.

Temperature, relative humidity, ventilation rates, lighting conditions (spectrum, intensity, and photoperiod), gaseous pollutants (eg, ammonia), and noise should be carefully controlled at all times and monitored as appropriate. Unstable environmental conditions can have a profound effect on the comfort, well-being, and metabolism of animals and therefore on the quality of experimental data derived. In general, temperature should be maintained at 68°–79°F (20°–26°C) for most rodents; 61°–72°F (16°–22°C) for rabbits; 59°–64°F (15°–18°C) for ferrets; 64°–84°F (18°–29°C) for primates, dogs, and cats; and 61°–81°F (16°–27°C) for most farm animals and poultry. Within these ranges, optimal systems should maintain temperatures within ±1°F of the set point. Relative humidity should be maintained at 30%–70% for most species and preferably within 10% of the set point. Ventilation rates should be 10–15 fresh air changes/hr. Air should not be recirculated unless it has been treated to remove particulate and gaseous contaminants. Lighting should be distributed evenly and sufficiently intense to promote animal well-being and to allow personnel to observe the animals and to perform all husbandry and sanitation duties safely and effectively. Diurnal or day-night cycles, as determined by species' requirements, should be controlled by automatic timers to maintain circadian and neuroendocrine regulation. The microenvironment within certain types of caging may be very different from that of the macroenvironment of the room. Carefully conducted research is needed to more precisely define the optimal environmental and social conditions for each species or group of species at the cage level.

Bedding materials should be nonirritating, absorbent, free of chemical contamination and pathogens, and unpalatable. Adequate quantities should be used to dilute and limit contact with excreta, promote air quality and other environmental factors by suppressing microbial growth, and keep animals dry and clean between changes of bedding or caging. The major types of contact bedding used are derived from ground corncobs, hardwood chips, recycled paper, heat-treated softwood shavings, and virgin cellulose. Untreated softwoods are not recommended because they contain volatile oils that may alter hepatic enzyme systems and affect certain kinds of research. Depending on research requirements, bedding may be sterilized by autoclaving or irradiation before use or used as is.

Feed should be of adequate quantity, palatable, free of contaminants, nutritionally adequate, easily accessible, and provided using means that meet behavioral needs according to specific species requirements. Feeds specifically manufactured for research animal use are preferred, because they are more likely to be uniformly constituted, free of contaminants, of known shelf life, and mill dated. Feed should be manufactured, transported, stored, and used in ways that minimize its deterioration, contamination, or infestation. Most small animals consume food in relation to their energy requirements as influenced by the environment and dictated by their genotype and are fed ad lib; rabbits, laboratory carnivores, swine, aquatic amphibians, and primates may be restricted to measured quantities of feed each day. As a general rule of thumb, laboratory animals minimally consume 4%–6% of their body weight in food daily. In addition to commercially prepared and usually pelleted natural ingredient diets of varying specification (eg, quality control and assurance of ingredients), semisynthetic or completely synthetic diets and all-liquid preparations can be formulated for use in certain kinds of research. Autoclavable or irradiated diets are available for rodents and can be used when sterilization of feed is desired.

Potable, uncontaminated water should be provided in adequate quantities to meet specific species requirements. Quality assurance programs that measure pH, hardness, chemical content, and microbial load are recommended. Highly purified, deionized, acidified, chlorinated, or sterile water may be required under certain experimental or husbandry conditions. Water is usually provided ad lib in manually filled or automated watering devices. Particularly in the housing of rodents, an automated water supply enhances the advantages of ventilated caging systems and reduces operational costs/expenses, increases safety for animal care technicians, saves labor, reduces disruptions of the mice by caretakers, and provides consistently high water quality. The drawback of the use of automated drinking water supply for rodents is the risk of hypothermia, drowning, or dehydration of cage inhabitants as a consequence of failure of the in-cage water delivery valve.

Water quality is the most important environmental variable for aquatic species and a key determinant of health. Inadequate water quality or fluctuations of water temperature are physiologic stressors that impact the intake, digestion, and use of food; alter the immune system; and predispose to opportunistic infection. Water for aquatic vertebrates should be free of nitrite, ammonia, and chlorine, with total coliform counts not exceeding 200/mL. The pH should be 6.5–8.5. While aquatic amphibians may be maintained in small containers of standing water, water recirculation with biologic filtration and periodic partial replenishment with fresh water, just as with fish, are helpful in suppressing bacterial counts and preventing the build-up of toxic chemicals. The ideal water temperature range for maintaining the aquatic amphibians used most popularly in research, the tetraploid South African clawed frog (Xenopus laevis) and the axolotl (Ambystoma mexicanum), is 65°–72°F (18°–22°C). For Xenopus tropicalis, a smaller, more rapidly maturing, diploid species of clawed frog from forested west Africa, water temperature should be 70°–85°F (21°–29°C). (Also see Amphibians.) Zebra fish and other tropical species used in research are best maintained at a consistent water temperature within the range 80°−90°F (27°–32°C).

A uniformly high level of animal enclosure and facility sanitation is mandatory to ensure that animals are clean and dry, air quality is adequate (without using masking agents), and primary enclosure surfaces and accessories are clean. Housing rooms and ancillary support space should be cleaned and sanitized as often as necessary to keep them free of dirt, debris, and potentially harmful contamination. For rodents in solid-bottom cages, usually 1–3 changes per week will suffice; for rodents, rabbits, and nonhuman primates in suspended cages over excreta pans and for mice in ventilated caging systems, cage changes every other week should be adequate. For larger animals, excreta and soiled bedding should be removed daily, and primary enclosures cleaned and sanitized daily, or at minimum every other week. Water bottles and other watering or feeding devices should be cleaned and sanitized at least weekly. Automated watering devices on cages, racks, or in rooms should be designed and programmed to flush continuously or regularly or they should be manually drained, rinsed, and sanitized at regular, frequent intervals. Heating cages and other equipment to 180°F (82.2°C) or using appropriate chemical disinfection (eg, hypochlorite solutions) kills nonspore-forming pathogenic bacteria and viruses. All caging and other equipment should be rinsed thoroughly after treatment with detergents or disinfectants. The effectiveness of the programs of sanitation should be evaluated regularly using appropriate microbiologic, organic material detection systems or other means.

Professionally directed programs to prevent, identify, and eradicate or control insects or escaped, feral, or wild rodents must be instituted, regularly scheduled, and consistently documented. The use of pesticides should be as a last resort and generally be confined to areas not used for animals or for storage of feed or bedding. If these agents are used in proximity to animals or their food and bedding, researchers should be informed of the use. Relatively inert substances, such as silica aerogel or boric acid powder, are recommended and are useful for control of crawling insects, eg, cockroaches.

Last full review/revision June 2013 by Michael J. Huerkamp, DVM, DACLAM

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