National Toxicology Program

National Toxicology Program
http://ntp.niehs.nih.gov/go/9989

2-Year Study Protocol

The purpose of this study is to determine the toxicologic and/or carcinogenic effects of long-term exposure on rats and  mice.

  1. Treatment:

    After a 10- to 14-day quarantine period, animals are assigned at random to treatment groups. Rats and mice receive the test agent for 104 weeks via a defined route of exposure at 3 treatment concentrations plus controls. Animals have continuous ad libitum access to dosed-feed and dosed-water in those exposure studies. For inhalation, gavage and dermal studies, animals are treated five times per week, weekdays only. Male mice are housed individually and rats and female mice are group-housed, except for inhalation and dermal exposure studies in which all rats and mice are housed individually.


    Animals Sexes Species Test
    Groups
    Total
    Treatment 50 x 2 x 2 x 3 = 600
    Controls 50 x 2 x 2 x 1 = 200
    Sentinel Animals 15 x 2 x 2
    x - = 60

    ___
    Total
    860
  2. Observations:

    Individual animal body weights for test and control group animals are recorded on day one on test and at 4-week intervals thereafter except for dosed-feed and  dosed-water studies, which are recorded weekly for the first thirteen weeks and monthly thereafter. If life-threatening tumors develop, a significant number of deaths occur, or a significant effect on body weight is observed, the weighing frequency may be increased to every two weeks.

    Animals are observed twice daily at least six hours apart (before 10:00 am and after 2:00 pm including holidays and weekends) for moribundity and mortality. Animals found moribund or showing clinical signs of pain or distress are humanely euthanized. Formal examinations for clinical signs of toxicity are made and recorded at four-week intervals. For dosed-feed or dosed-water studies, food consumption/water consumption is measured and recorded weekly for the first thirteen weeks and monthly thereafter.

  3. Necropsy and Pathology:

    Necropsy: A complete necropsy is performed on all treated and control animals that either die or are sacrificed. All tissues required for complete histopathology are trimmed, embedded, sectioned and stained with hematoxylin and eosin for histopathologic evaluation. (necropsy list)

    Histopathology: All animals in all treatment groups that die (or are sacrificed in a moribund condition) and those that complete the 104-week exposure are subjected to a complete necropsy and slides of all tissues required for complete histopathologic evaluation are prepared and evaluated. (histopathology list)

The NTP is located at the National Institute of Environmental Health Sciences, part of the National Institutes of Health.