Analysis of environmental sound levels in modern rodent housing rooms

Abstract

Noise in animal housing facilities is an environmental variable that can affect hearing, behavior and physiology in mice. The authors measured sound levels in two rodent housing rooms (room 1 and room 2) during several periods of 24 h. Room 1, which was subject to heavy personnel traffic, contained ventilated racks and static cages that housed large numbers of mice. Room 2 was accessed by only a few staff members and contained only static cages that housed fewer mice. In both rooms, background sound levels were about 80 dB, and transient noises caused sound levels to temporarily rise 30-40 dB above the baseline level; such peaks occurred frequently during work hours (8:30 AM to 4:30 PM) and infrequently during non-work hours. Noise peaks during work hours in room 1 occurred about two times as often as in room 2 (P = 0.01). Use of changing stations located in the rooms caused background noise to increase by about 10 dB. Loud noise and noise variability were attributed mainly to personnel activity. Attempts to reduce noise should concentrate on controlling sounds produced by in-room activities and experimenter traffic; this may reduce the variability of research outcomes and improve animal welfare.Noise in rodent housing facilities is rarely controlled as an environmental variable and is often monitored only in areas where human hearing may be at risk, such as cage washing facilities. This lack of environmental control contrasts with the stringent monitoring that is standard for many other aspects of rodent housing, such as veterinary care, infection status, sanitation, heating, ventilation and air conditioning. Noise can directly affect auditory studies by damaging subjects' hearing, and it can indirectly affect many other aspects of research by causing animals physiological stress [1][2][3][4][5] . Involuntary exposure to noise is recognized as a source of distress in humans, and by extension, there may be appreciable animal welfare concerns if the noise in the animal facility is loud enough to cause stress, cause hearing damage or disrupt sleep.To our knowledge, the most recent comprehensive surveys of variability and sources of noise in rodent housing rooms were conducted between 10 and 20 years ago 1-3 . These surveys showed that noise levels varied significantly during the work day but not during non-work hours 1 . Sources of noise included mechanical systems, electronics, utilities such as running water and telephones, sanitation equipment and animal care activities 2,3 . Many of these sources produced sounds in the range of mouse hearing 1-3 .In the years since the publication of those surveys, noise-generating mechanical infectioncontrol systems such as individually ventilated cages and cage changing stations have become

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