Housing and husbandry conditions can have large, unforeseen and undesirable influences upon the best planned scientific studies, whereas animals coping well with their surroundings will deliver the most scientifically valid information in an experiment.
Sufficient attention must be made to the animals’ instincts and needs from birth to death. Since most animals are more active in one phase of the 24-hour period, environmental influences may easily be overlooked, particularly if the animals are nocturnal. Issues to be discussed while planning animal studies include:

  1. The acclimation period (its anticipated duration, and the criteria for assessing its success)
  2. The parameters to be measured during acclimation and the study itself, such as body weight, feed intake, body temperature and behavioural signs
  3. Group or solitary housing of both sexes, stocking densities, the effects of removal of animals from a group, the effects of pain and distress on co-habitants, and environmental effects caused unwittingly by conditions in the holding area (e.g. tank, cage, pen or pasture), including the position of cages/tanks in a room
  4. The size and shape of the housing, including provisions for social and environmental enrichment. Any lowering of minimum standards (e.g. those described in Annex III of the EU Directive 2010/63) must be described and justified, along with the likely effects on the animals and measures to mitigate these.
  5. The possible negative welfare effects on the animals of the housing conditions, among other things by preventing natural behaviour, which may lead to contingent suffering. This has the potential to cause as much, if not more, suffering than the experimental procedures themselves, as well as the capacity to confound the science.
  6. Room temperature, relative humidity, water temperature in the case of aquatic species, and acceptable limits for these.
  7. Photoperiod, light intensity and noise levels. As well as providing suitable lighting during activity periods, species-specific requirements for adequate sleep must also be met. This is particularly important after physiologically stressful procedures, such as surgery. Sudden noises such as fire alarms or rapid movement by personnel to whom the animals are not accustomed may be more stressful than constant low-level background noise. Seasonal breeders may require a period of torpor, which must be taken into account.
  8. Bedding, nesting material, hiding places and (for aquatic species) the presence and type of bottom substrate
  9. Procedures for cleaning and disinfection, which may be particularly difficult to achieve in breeding colonies
  10. The type and composition of feed, as well as any pre-treatment, including the method and frequency of administration. Nutrient reactions with the test substance or procedure may mask or increase a response to the latter.
  11. Justification for the necessity and length of food or water deprivation, its likely effects on the animals (which will be related to the time of day when it is planned) and the avoidance of overfeeding.
  12. Water quality and quality control. This will be particularly important for aquatic species, where relevant parameters will include:
    • Water source and pre-treatment
    • Turbidity and conductivity
    • Oxygen content
    • pH, ion strength, salinity and nitrogen content
    • Flow and the number of water changes per hour
    • Recirculation methods and treatment

These may be affected by the type of tank or pen and its size, shape, colour, water level, cleaning routines and light sources.

Other environmental factors include the effects of noise, local ventilation rates (e.g. in individually ventilated cages), ultrasound and the presence of personnel (habituation to their activity, noise levels and odour). In some experiments it may be necessary to consider factors whose physiological effects are less certain, such as the earth's magnetism, air pressure, seasonal changes and lunar cycles.

A large number of references to papers describing the effects of housing and husbandry methods are cited in a paper introducing the IMPROVE guidelines for in vivo models of ischaemic stroke.

Housing and Husbandry. NC3Rs guidelines for rodents, ferrets, rabbits, cats, non-human primates, dogs and guinea-pigs
Guidelines for housing and management of research animals
General advice about using farm animals in research
Guidelines for the care and use of farm animals in research
Guidelines for the care and use of birds in research
Guidelines for nutritional research
Guidelines for fasting (food deprivation) in rodents
Guidelines for the use of non-human primates
Guidance on the care and housing of fish, including environmental enrichment, and other aquatic species.

More references

Benefits of enrichment pass to next generation of lab mice
Overview of scientific papers on the effects of relative humidity on health and wellbeing of laboratory mice and rats (Karen Ekkelund Petersen, Scanbur)
The effect of relative humidity on water intake of C57BL/6J mice housed under conditions of controlled relative humidity at cage level
The common use of improper control diets in diet-induced metabolic disease research confounds data interpretation: the fiber factor
Imprecise diet reporting affects metabolic animal research results 
Unsterilized feed as the apparent cause of a mouse parvovirus outbreak
Must ad libitum mean always available?
Refinement of the use of food and fluid control as motivational tools for macaques used in behavioural neuroscience research: report of a Working Group of the NC3Rs
A possible link between food and mood: dietary impact on gut microbiota and behavior in BALB/c mice
The role of the gut microbiota on animal model reproducibility
What is really in our drinking water?
Laboratory mouse housing conditions can be improved using common environmental enrichment without compromising data
Tickling improves laboratory rat welfare

The 9 to 5 Rodent − Time for Change? Scientific and welfare implications of circadian and light effects on laboratory mice and rats
Are vivarium husbandry schedules at odds with mouse sleep patterns?
Light and the laboratory mouse
Noise in a laboratory animal facility from the human and mouse perspectives
Animal stress due to noise and vibration 
Making sense of it all: The importance of taking into account the sensory abilities of animals in their housing and management
Mouse Ethogram (methods, protocols and background information)
To Group or Not to Group? Good Laboratory Practice for Housing Male Laboratory Mice
Evaluation of the effects of space allowance on measures of animal welfare in laboratory mice
The effect of virtual fencing stimuli on stress responses and behavior in sheep (Kearton et al., 2019)
Rat cognition and environmental enrichment
Vivarium vs Wild: Which is the best setting for animal research?
Are happy lab animals better science?
NC3Rs/AstraZeneca Workshops on rat behaviour
Norway Rat Behavior Reportoire

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