Food and Water Restriction in Mice and Rats

Policy

When mice and rats are taken out of a housing room’s rack to be transported and held in animal facility procedure room or in a researcher lab outside of the facility, the cages of mice and rats should be provided with a water source (e.g. Hydropac®, water bottle or Hydrogel®) especially if they will be removed from an automated water system for greater than 4 hours for mice and 6 hours for rats.

When short-term food restriction is used to provide an empty stomach for gavage, typical gastric emptying times in mice and rats should be considered and fasting longer than 4 hours for mice and 6 hours for rats would require strong scientific justification.

Dietary or water restriction must be scientifically justified and approved by the IACUC. Explanation of the suitability of the proposed regimen for the species and experiment is required. If food or water restriction is to be used for behavioral research, it must be of minimum severity to achieve the desired behavioral outcome (Nat’l Research Council 2011). Positive reinforcement methods, such as the use of desirable food or fluid ‘treats’ to motivate behavior, should be considered thoroughly before proposing a food or fluid restriction paradigm. Less severe dietary or fluid restriction may be needed after a period of initial training, and adjustments in degree of restriction should be made accordingly. Whenever an animal obtains any portion of its diet through food or water reward, the sum of the food and water earned through reward and that of ad libitum must be sufficient to maintain the animal in a healthy state without a significant loss of weight. In accordance with 2013 NIH Guidelines for Diet Control in Behavioral Research Studies, Veterinary Services must be informed if an animal shows signs of clinical dehydration, including but not limited to increased skin turgor or sunken eyes. Unless otherwise approved by the IACUC, intake must be increased immediately if an animal loses 20% of its pre-study body weight while food- or water-restricted until the weight is regained. A plan for this must be outlined in the animal use protocol. Investigators working with young animals should specifically address the need for dietary requirements for normal growth. Normal growth curves have been published for many laboratory rodent strains, and should be referenced when developing a food or water restriction plan for growing animals.

When food or water is not provided ad libitum, either the animal should be permitted to earn food and fluids to satiety during the period of behavioral training, or its intake should be appropriately supplemented on a daily basis. Food and fluid should be made available simultaneously during behavioral training and/or supplementation to minimize dehydration-related anorexia (Toth and Gardiner, 2000). In cases where supplements are required, the amount of food and fluids to be provided daily should be equivalent to the amount typically consumed by the animal with ad libitum access or a mildly restricted amount (for example, 80% of consumption) if necessary for the experiment, and specifically approved by the IACUC. Pre-restriction data must be obtained in order to determine the appropriate restriction amount or reference ranges must be provided to the IACUC. Transitions from ad libitum access to food or water restriction should be gradual, over the course of one or more days to minimize animal stress unless otherwise explained in the IACUC protocol. When access to food or water is time-limited, it should be made available at consistent times during the animals’ light/dark cycle to allow behavioral accommodation to the study schedule.

When used as a behavioral motivator, the type and concentration, if applicable, of the food and fluid reward must be specified in the IACUC protocol. Food and fluid reward items should pose minimal risk of introduction of pathogens to specific pathogen free animals. Irradiated or autoclaved food items manufactured to be used as rodent behavioral rewards are preferable to food items from other sources, and the use of non-irradiated or autoclaved items would need to be strongly justified in the IACUC protocol. Food items that are nutritionally balanced for rodents should be selected if the majority of the animals’ daily food intake occurs during motivated behavioral testing.

Each animal under food or fluid restriction must be observed and weighed at least daily by trained and experienced investigative staff. Daily weight and intake records must be maintained and be available for review by Veterinary Services and the IACUC. All food or water restriction protocols should clearly state how the animals’ health is monitored and include criteria for intervention, such as weight loss, decreases in body condition, and/or clinical signs of dehydration.