Cost Comparison of Rodent Soiled Bedding Sentinel and Exhaust Air Dust Health-Monitoring Programs

  • Executive Summary – JAALAS Article September 2020

    Animal research facilities have traditionally used soiled bedding sentinel (SBS) health-monitoring programs to detect and exclude adventitious pathogens that could affect research results; however, exhaust air dust (EAD) health-monitoring has been evaluated by several groups and proven to provide increased sensitivity for the detection of pathogens and to be more efficient in detecting pathogens when used as a complete replacement for traditional SBS programs.

    This improved detection of multiple pathogens through Sentinel EAD monitoring was the primary factor in The University of Chicago’s decision to switch to an EAD program. Having Allentown’s IVC racks already in place, the University implemented Allentown’s Sentinel™ EAD® solution which uses a specific holder that captures EAD on a collection medium that ultimately undergoes PCR analysis.

    After implementing EAD, the University conducted a study—the first of its kind—to examine the detailed cost differences between SBS and EAD health-monitoring programs.

    Cost Savings Advantage with Sentinel EAD

    The study compared the annual costs of SBS and Sentinel EAD health-monitoring programs at the University. The annual cost of the Sentinel EAD program was found to be $160,800 less expensive than the SBS program, a 26% cost savings (Table 1).

    Table 1. Comparison of the total annual costs of SBS and EAD health-monitoring programs.
    Annual Cost (US $)
    Type of Cost Soiled Bedding Sentinels Sentinel EAD
    Sentinel Mice Ordering 15,084 Not applicable
    Sentinel Mice Shipping 3,876 Not applicable
    Sentinel Mice Maintenance 137,642 Not applicable
    Veterinary Technician Time 7,190 1,683
    Diagnostic Testing 449,629 450,938
    Total Annual Cost 613,421 452,621

    Overall, the study showed a considerable cost savings with the Sentinel EAD program which eliminated the need to purchase and maintain animals. EAD also decreased the amount of time spent by animal care staff on heath-monitoring activities. Furthermore, the EAD program replaced the use of live sentinel animals therefore reducing the associated annual usage.

    Decreased Animal Care Staff Labor with Sentinel EAD/Increased Per Diem

    On top of providing cost savings, the Sentinel EAD program substantially reduced the amount of animal care staff time required when compared to the SBS program. This savings amounted to 150 hours per year, or almost 3 hours each per week, for the veterinary technician.

    Animal care staff also saved time not having to move soiled bedding during cage change which was not calculated in this study but was an expected benefit. Additionally, 419 more cage slots became available for investigator use and increased per diem for these cages.

    These considerable savings in cost, time, and space accomplished with Sentinel EAD would be highly beneficial to any laboratory animal program.

    Cost Analysis

    The costs of SBS were calculated by totaling the sentinel animal ordering and shipping costs, the maintenance cost of the animals, percentage of the veterinary technician’s yearly wage spent on the program, and diagnostic testing costs. The costs of EAD were calculated by totaling the percentage of the veterinary technician’s yearly wage spent on the program and diagnostic testing costs.

    The significant cost savings resulted from the animal ordering and maintenance expenses, which are not necessary in the Sentinel EAD program. These cost savings depend on many factors, including the daily census and type of racks used in a facility.

    The surveillance testing costs depend on the pathogens analyzed and the frequency of testing. The testing frequency for this study was the same for both programs which permitted a direct comparison. When institutions switch to EAD monitoring, they can continue with the same pathogen screening list and testing frequency but should define and regularly evaluate this panel to ensure that they are testing for relevant pathogens and are not incurring expenses on unnecessary testing.

    Indirect costs such as overhead rates were excluded from this study since they are usually applied to direct labor hours, affecting the costs of both health-monitoring methods to the same degree and, therefore, provide no further differentiation. Also, overhead and other indirect costs, such as depreciation and amortization, may vary more widely between institutions than the direct costs tallied and, consequently, may be less meaningful when comparing the overall cost of SBS vs. EAD.

    Reduced Use of Animals (3R principles achieved) with Sentinel EAD

    Previous reports have speculated or approximated the reduction in animals used after switching to EAD monitoring. This University of Chicago study (Figure 1) is the first to determine the actual annual reduction in the number of animals used when an SBS program is replaced by a Sentinel EAD program.

    The EAD program significantly decreased the yearly use of live sentinel animals from 1,676 mice to zero. This element is consistent with the 3R (Replacement, Reduction, and Refinement) principles of animal research because using Sentinel EAD monitoring replaced the use of live animals.

    This reduced animal usage benefit complements the greater sensitivity of pathogen detection and efficacy in detecting pathogens as well as the cost and time savings realized when switching from traditional sentinel monitoring methods to Sentinel EAD.

    Study Conditions

    • Total housing capacity of the 3 vivaria = 21,000 cages
    • 231 single-sided IVC racks and 94 double-sided racks, all 70 cages / face (Jag 75 Micro-VENT Environmental System IVC Racks, Allentown Caging)
    • Sentinel animals: Female Swiss Webster Mice, aged 3-4 weeks (Taconic Biosciences)
    • 1 sentinel cage animal on each rack side (i.e. for 70 cages), with 2 sentinel animals per cage
    • One sentinel removed each calendar quarter for terminal diagnostic use, and replaced, resulting in a total sentinel use of 4 mice / sentinel cage / year, with a total of 1,676 sentinels ordered / year
    • Quarterly collection / replacement of exposed EAD medium
    • Teklad 7097 corncob bedding, 1⁄4 inch thick, autoclaved
    • Reverse-osmosis- treated water, automatic watering (Avidity Science)
    • Diet Teklad 2918 (Envigo), irradiated
    • Enrichment: cotton squares (Ancare) or specialty paper (Enviro-dri), autoclaved
    • Cage change every 14 days in a BSC-II A2 (NuAire)
    • Light cycle 12/12 hours, temperature 68-76°F and humidity 30-70%

    Figure 1. The University of Chicago’s study conditions for the cost comparison of SBS and EAD health-monitoring programs.

    To read the complete JAALAS article, click here.


    Luchins, K. R., Bowers, C. J., Mailhiot, D., Theriault, B. R., & Langan, G. P. (2020). Cost Comparison of Rodent Soiled Bedding Sentinel and Exhaust Air Dust Health-Monitoring Programs. JAALAS: Journal of the American Association for Laboratory Animal Science, vol. 59, no. 5, pp. 1-4.

    Sentinel EAD – Patent Pending, Allentown, LLC and Charles River Laboratories. Sentinel is a trademark of Allentown, LLC. EAD is a registered trademark of Charles River Laboratories, Inc.

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