The past, present, and future of National Aeronautics and Space Administration spaceflight diet in support of microgravity rodent experiments.

Rodents have been the most frequently flown animal model used to study physiological responses to the space environment. In support of future of space exploration, the National Aeronautics and Space Administration (NASA) envisions an animal research program focused on rodents. Therefore, the development of a rodent diet that is suitable for the spaceflight environment including long duration spaceflight is a high priority. Recognizing the importance of nutrition in affecting spaceflight physiological responses and ensuring reliable biomedical and biological science return, NASA developed the nutrient-upgraded rodent food bar (NuRFB) as a standard diet for rodent spaceflight. Depending on future animal habitat hardware and planned spaceflight experiments, modification of the NuRFB or development of a new diet formulation may be needed, particularly for long term spaceflights. Research in this area consists primarily of internal technical reports that are not readily accessible. Therefore, the aims of this contribution are to provide a brief history of the development of rodent spaceflight diets, to review the present diet used in rodent spaceflight studies, and to discuss some of the challenges and potential solutions for diets to be used in future long-term rodent spaceflight studies.

Oxidative and nutrient stability of a standard rodent spaceflight diet during long-term storage.

The National Aeronautics and Space Administration's standard spaceflight diet for rodents is the nutrient-upgraded rodent food bar (NuRFB). The shelf life of the NuRFB needs to be determined in order to avoid malnutrition of rodents and confounding of research results resulting from nutritional deficiency. The authors compared the oxidative and nutrient stability of NuRFBs stored at either ambient temperature (26 °C) or at refrigeration temperature (4 °C) for use in long-term rodent feeding experiments. After 0, 3, 6, 9 and 12 months (mo) of storage, lipid oxidation, fatty acid composition and amounts of specific vitamins and amino acids in NuRFBs were analyzed. No oxidative rancidity developed in NuRFBs stored at 4 °C for up to 12 mo, but NuRFBs stored at 26 °C for 6 mo developed oxidative rancidity and had reduced amounts of γ-linolenic acid (18:3n-6). Despite loss of vitamin E, vitamin A and thiamin after storage at 26 °C for 12 mo, vitamin levels in NuRFBs remained at or above the levels recommended for optimal rodent health. The amino acid profile of NuRFBs was unaffected by storage at 4 °C or 26 °C for 12 mo. The results suggest that NuRFBs stored at 4 °C for up to 12 mo and NuRFBs stored at 26 °C for up to 6 mo provide suitable nutrition for rodents in long-term experiments.

Evaluation of the nutrient-upgraded rodent food bar for rodent spaceflight experiments.

OBJECTIVE: Selection of an appropriate diet for rodent spaceflight experiments is critical and may have significant effects on mission results. The National Aeronautics and Space Administration (NASA) rodent food bar (RFB) was reformulated and designated as the nutrient-upgraded RFB (NuRFB). The objectives of this study were to determine whether the NuRFB nutrient formulation meets the 1995 National Research Council (NRC) nutrient recommendations and whether the NuRFB can be used for short-term (45-d) and long-term (90-d) spaceflight experiments. METHODS: Nutrient and moisture analyses of the NuRFB were performed. Young (age 13-14 wk) male Sprague-Dawley rats (n=16/group) were individually caged and fed a diet treatment consisting of 1) NuRFB, 2) RFB, or 3) modified AIN-93G containing 4% instead of the 7% fat for 45- or 90-d. At the end of the study, organs were weighted, and serum clinical chemistry indicators of organ function and hematologic measurements were determined. RESULTS: Chemical analysis of the diet ingredients showed that the NuRFB met the 1995 NRC nutrient recommendations for rats. Subsequent animal feeding studies showed that NuRFB was comparable to RFB and modified AIN-93G for supporting rat growth and body weight maintenance. In addition, the safety of the NuRFB for use as a spaceflight diet was indicated by the absence of changes in organ weight or function. CONCLUSION: Based on the study results, the NuRFB performed similarly to the RFB and met the criteria necessary for short-term and long-term rodent spaceflight experiments.