factors (variables) affecting animal research data validity

variables that ARE easily recognized & controlled

• diet

• environmental temperature

• humidity

• ventilation

• light cycle

• water

• noise

variables that are NOT easily recognized & controlled

• animal genetics

• latent disease

• environmental contaminants

• microbial transmission

• subtle behavioral stressors

• idiosyncratic reactions

humidity

• ideal: 40-70% RH

• maintenance of the “thermoneutral zone”

• appropriate humidity levels facilitate thermoregulation

humidity monitoring

• central computer system

• gauges

• sling psychrometer

• hygrothermograph

low humidity

• occurs in winter when heating systems dry the air

• occurs in areas where desert-like conditions exist

• leads to increased dust accumulation in the air, the room, and in cages

• can adversely affect the mucociliary apparatus

• can cause “ringtail” in young rats

• rectify with humidifiers in the HVAC system

• rectify with individual room humidifiers

• <40% RH

problems associated with dust

• bacterial & viral particles can adhere to dust

• air currents (eddy currents) can disseminate the contaminated dust particles throughout the room

mucociliary “escalator”

→ rhythmic/synchronized movement of the cilia in air passages moves the overlying mucus layer and the inspired particulate matter up the trachea where it is expelled

→ with low humidity, the mucus layer dries up and the cilia stop moving, allowing particulate matter to accumulate deep within the lungs, increasing the chance of infection

high humidity

• >70% RH

• occurs in rooms with autoflush rack pans

• occurs in cages with filter tops which are not frequently changed

• reduces resistance to infection

• increases predisposition to heat stress when temps are above recommended levels

temperature

• affects animal body temperature

• high or low body temperatures affect metabolism and activity

• recommendations established for room temperatures, but do not address microenvironmental temps inside of the cages

temperature monitoring

• central computer system

• gauges

• hygrothermograph

• room high/low thermometers

microenvironmental temperature factors

• room temperature & humidity

  • higher humidity makes the room “feel” hotter

• cage design

  • ventilation/air exchange- suspended wire versus shoebox, filtertop versus open

• cage population

  • heat produced by animals- single-housed vs multihoused

• activity of the animals

  • ± heat production by animals

• amount & velocity of ventilation at cage level

  • static filter top cages

  • high throughput individually ventilated cages

below the thermoneutrality zone

→ adaptations to minimize heat loss:

• peripheral vasoconstriction- dermal toxicology study effects

• increased metabolic activity- increased food consumption, variation in biological response

→ adaptations to minimize heat acquisition:

• peripheral vasodilation

• decreased metabolic activity- decreased food consumption

• decreased reproductive performance

• decreased lactation

temperature control

• daily monitoring & adjustments

• air conditioning/heating systems

• humidity control

• limited cage populations

ventilation

• provides or removes heat as needed

• removes waste gases (carbon dioxide & ammonia)

• reduces dust & particulates in the air

• removes odors

• affected by cage design

low exchange/flow rates on ventilation

• increased carbon dioxide levels

• increased ammonia buildup

• increased dust buildup

• may lead to increase in relative humidity (RH)

potential ammonia levels in rodent caging

• can adversely affect the eyes and respiratory passages

• ciliostasis occurs in respiratory passages at ~5 ppm

• human nose detects ammonia odor at >25 ppm

ventilation achieved with:

• HVAC systems (heating, ventilation, & air conditioning)

• individually ventilated cages/racks

• exhaust fans

• outdoor open-air facilities

ventilation ideal criteria:

• 10-15 (100%) air changes per hour [non-recirculating]

• reduce airborne particulate contamination

• reduce odors

ventilation→ high exchange/flow rates (>16/hr)

• may lower temperature and “chill” the animals

• may lead to decrease in relative humidity (RH)

• greatly increases utility costs

HEPA filtration

• high efficiency particulate air (HEPA) filter

• removes particles sized ≥ 0.3μ

• keeps airborne disease organisms out, or prevents release of airborne infectious agents

standard filtration

• simple dust filters on supply air

• charcoal impregnated filters to remove odors

air currents

affect particulate, waste gas, and odor removal

• can increase or decrease contamination potential in cages

airflow patterns → exhausts near ceiling inlet

• “short circuiting” of airflow
• inadequate airflow / exchange in lower part of room

exhausts near floor level

• increased eddy current formation

• more widespread dissemination of particulates in air

exhausts in floor under inlets

• decreased eddy current formation

• “dead space” in areas without inlets or exhausts

laminar airflow room

• entire surfaces of ceiling & floor are perforated

• air moves in a uniform direction

• virtually eliminates eddy currents

• greatly reduces level of particulates in the air

room air pressure

→ referred to as air “balance”

• differential air pressure between animal room & hallway

positive room air pressure

• positive with respect to the hallway

• protects room occupants from contamination

• hallway has a higher exhaust flow rate to make it negative with respect to the room

negative room air pressure

prevent escape of disease agents or toxic airborne chemicals from the animal room into the common hallway, contaminating other rooms or staff (e.g., in rooms with infectious disease research or use of toxins or hazardous chemicals)

intentional exposure

anesthetics, analgesics, tranquilizers, parasite treatments, antibiotics

unintended exposures

air, water supply, feed, bedding, caging, equipment

clean/dirty corridor systems

• room negative with respect to the clean hallway

• protects room occupants from contamination from other rooms

• dirty hallway has a higher exhaust flow rate to make it negative with respect to the room

• traffic patterns - movement of people, equipment, and supplies must be strictly adhered to

assessing air balance/flow

• central computer monitoring

• air velocity meter [anemometer] (inflow & exhaust measurements)

• Magnehelic gauge on wall in hallway

• airflow tubes & indicators (penetrates wall)

• non-toxic smoke testing

noise

induction of stress; hearing damage/deafness; audiogenic seizures in gerbils and rabbits

auditory effects

• injury to inner ear, affecting hearing

• OSHA permissible level : <85db (decibels)

• short term 160db - mechanical damage to inner ear

• short term 140db - “pain”

• long term 100db - inner ear damage

light

retinal damage; cataract formation; altered circadian rhythm

cage design

• influences the amount of air, light, & sound an animal receives

• influences the amount of heat, humidity, & gaseous waste released into the macroenvironment

• cage materials should be non-consumable

• provide security to prevent escape

• free of projections/defects which might cause injury

• opacity, translucency, or transparency may be stressful

• visual barrier needed for nonhuman primates

• filtertops reduce air exchange, allow heat buildup

• galvanized cage floors may have spikes that can

penetrate feet (causing “bumblefoot”)

• flooding of cages can lead to drowning or hypothermia

• autowater systems may allow spread of

microorganisms

stress

• activation of the adrenal cortex via the pituitary gland

• leads to “injury” of elements of the immune system

• stimulates the “flight or fight” response, with release of hormones affecting the cardiovascular system