Some considerations for the development of diets for mature rodents used in long-term investigations

Nutritional requirements for mature rodents used in long-term investigations are virtually unknown. The limited knowledge of the dietary needs of mature rodents is due in part to overreliance on weanling animals fed an experimental diet for relatively short periods. Generalizations made from observations of weanling rodents are not appropriate for all ages. Dietary recommendations for rodents have been established, for the most part, by using the nutritional benchmark of maximal growth rate in animals fed ad libitum. Although this method provides valuable insight into the understanding of nutritional deficiency, it is less effective in determining nutrient requirements for mature animals used for the long term. The implication that maximal growth resulting from ad libitum feeding may not indicate the best dietary regimen in the long term is consistent with the observation that energy-restricted rodents live significantly longer and have lower incidence of disease that do their ad libitum-fed counterparts. These and other findings discussed in the review suggest that nutrient requirements established for young rodents may need re-evaluation to determine their applicability to the dietary recommendations for older animals used in long-term investigations.