Acoustical Society of America
158th Meeting Lay Language Papers

Developing Acoustical Criteria for Rodent Housing Facilities

Kimberly Lefkowitz - kim@cstiacoustics.com
CSTI Acoustics
16155 Park Row Suite 150
Houston, TX 77084

 

Popular version of paper 3aAB9
Presented Wednesday morning, October 28, 2009
158th ASA Meeting, San Antonio, TX

 

Laboratory animals (rats and mice) and the research that involves them are responsible for tremendous advancements in medical science.  In order to reduce unknown effects in these controlled experiments, many aspects of the animal's environment are tightly regulated including: lighting, food and water intake, and air quality.  Noise levels and frequency should also be monitored to ensure that high noise levels are not affecting the animals.  Measuring levels that affect rodents is particularly complicated because it requires measuring up to 91,000 Hz, significantly above the hearing threshold of humans.

 

Though current regulations include detailed standards for air quality and care and treatment, there are very few guidelines as to what criteria to follow with regard to noise.  High noise levels have been shown to cause effects such as audiogenic seizures (seizures caused by exposure to sound), atypical responses to drug treatments, elevated blood pressure, elevated water consumption, decreases in blood sugar, decreases in insulin levels, hypertension, changes in reproduction function, immune responses, increases in tumor resistance, and hearing loss.  European standards for individually ventilated cage racks are based on testing parameters developed by the Center for Biomedical Research of the Faculty of Medicine in Germany.  There is some mention of noise, but no specific levels are identified.  The National Research Council of United States has suggested a criterion of 85 dB.  Adverse effects have been seen as low as 75 dB, however, so a criterion of 85 dB is not sufficient to prevent the rodents being affected by environmental noise. In addition, the NRC criterion does not indicate that the entire hearing range of the rodents should be considered.  The purpose of this work is to develop preliminary acoustical criteria for laboratory rodents.

 

In order for a criterion to be effective it must have several important characteristics.  First, the criterion must indicate an acoustic level below which adverse affects have not been observed.  Second, it must take into account all frequencies that the animal can perceive and emphasize the frequencies to which the animals are most sensitive.  Third, the criterion must also acknowledge the rodents’ current state of activity -- sleeping animals are more sensitive then active animals.  It should be noted that rodents are nocturnal.

 

In order to address the first aspect, previous research has been studied.  There has been extensive research regarding the effects of noise on laboratory animals.  All of the side effects discussed above can interfere with medical research studies.  Therefore, it has been determined by a number of researchers that a sound and vibration criteria is needed.  Adverse effects have been seen as low as 75dB.  Some studies suggest that stress factors have been seen as low as 55 dB.  These levels were usually in the audible frequency range for humans (16 Hz – 20 kHz).  Since mice can hear up to 91 kHz, criteria that focus on sounds in the range of 16 Hz – 20 kHz are not particularly helpful in determining the effects of noises in the upper part of the rodent hearing range.  Research facilities often contain sources of ultrasonic sound including some laboratory equipment, squeaking doors and carts, cage washing noises, and alarms.

 

To address the second facet, the hearing sensitivities of these rodents must be identified.  For the purpose of this paper, the focus will be on the hearing of mice and rats; however, these criteria could eventually be extended to include the hearing ranges of other animals if needed.  Figure 1 shows the hearing sensitivities of mice, rats and humans as presented in the technical literature.  The rodent hearing tests were done by Kelly and Masterson, who observed the behavior of the animals when a single frequency was played at various levels.  The behavior of the animal was expected to change when the sound became audible.

 

Figure 1. Threshold of Hearing Curves

 

There is definitely a similar shape to the three sensitivities and a similarity in the levels of sensitivity.  These similarities have been exploited to develop preliminary criteria for consideration.  Because there has been exhaustive research into the criteria applied to human noise levels, we can examine these criteria for inspiration.  The criteria ranges, shown in figure 2, are suggested for active periods and rest periods for humans.  The active criteria are suggested for moderately fair listening conditions such as in laboratories, lobbies, corridors, etc.   The threshold of human hearing is shown for comparison.

 

Figure 2. Human Criteria

 

To develop criteria for rodents, we exploited the similarities in the thresholds between humans and rodents. We examined the difference between the threshold and the criteria for humans; we then translated the criteria into the higher rodent hearing range.  If both the rat and the mouse hearing curves are combined to account for the most sensitive frequencies, then we can develop preliminary criteria for acceptable noise levels for both sleep and active periods.  There should also be a maximum level that should not be exceeded more than 5 percent of the time.  This is included to make sure that levels where adverse effects are seen are kept to a minimum.  These curves are shown in figure 3.

 

Figure 3. Rodent Criteria

 

Clearly these are preliminary acoustical criteria to be reviewed and considered by:

 

·         - Researchers in veterinary medicine who will have the opportunity to observe animal behavior and

·         - Architects and engineers who are designing animal housing facilities.

 

It is likely that as additional information and input become available, this criteria will be updated.  (It is interesting to note that noise criteria for humans has been reviewed and modified six times during the past 50 years.)

 

For new facilities, we recommend that the sound level should be monitored during the early stages of inhabitation to ensure that the noise levels do not exceed the levels shown above.  The monitoring should be done while the animals are in residence to take into account the sound of the animals themselves and the sound made during the care of the animals. 

 

The purpose of these preliminary criteria is to encourage professionals engaged in administering, designing, and constructing animal housing facilities to seriously consider the impact of noise in their facilities.