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Food & Fluid Restriction

Restriction of an animal's food or fluid intake is used for various research purposes. However, it has been shown that some methods of food and/or fluid restriction are physiologically and/or psychologically stressful and, if restriction is allowed to exceed acceptable levels, can be physically harmful to an animal. Regardless of the purpose, the amount of food/fluid restriction used should be the minimum level that will achieve the objective.

If food/fluid restriction other than an accepted pre-anesthetic fasting procedure is to be used in an experimental protocol, the method of restriction and scientific justification for its use should be clearly explained in the protocol form submitted for IACUC approval. Restriction must be based on a measurable parameter such as percentage of ad libitum intake, percentage of body weight compared to a (paired; ad libitum intake) control animal, or length of time access to food/fluid is allowed per 24 hours.

Nutritional research often requires the alteration of nutrient content in an animal diet rather than a restricted intake of food. The principal investigator is responsible for assuring the proper formulation and nutritional adequacy of diets used in these studies. Rations developed for nutrition studies frequently vary in form and palatability. Arrangements should be made to insure that animals consume an adequate amount of the ration.

In order to make a knowledgeable determination of an appropriate level of food/fluid restriction it is necessary to know what normal quantities of food or fluid are required for maintenance of the species in question. Life stage (growth, pregnancy, lactation, geriatric) and state of health must also be taken into consideration in determining maintenance requirements. Unless scientifically justified, the animal should be slowly adapted to the level of restriction. All food/fluid-restricted animals must be monitored for signs of distress.

Signs of distress may include:

  • Rapid weight loss
  • Poor body condition
  • Muscle wasting
  • Prominent bones
  • Sunken eyes
  • Poor hair coat
  • Lethargy or other behavioral changes
  • Dehydration which can include the following signs:
  • Decreased urine production
  • Constipation
  • Dry mucous membranes
  • Sunken eyes
  • Crusting around eyes and nose
  • Loss of skin elasticity

Investigators must monitor food and /or water consumption daily and maintain records of individual body weights throughout the restrictive period. Required frequency of body weight monitoring will vary with species with once a week as a minimum. Small animals with high metabolisms such as rats and mice or animals with metabolic disturbances will require monitoring on a more frequent basis. See the Penn State IACUC Guidelines on Food or Fluid Restriction for further information.