Nutrient intake and growth characteristics of male Sprague-Dawley rats fed AIN-93M purified diet or NIH-31 natural-ingredient diet in a chronic two-year study.

BACKGROUND AND AIMS Daily nutrient intake and growth of male Sprague-Dawley (SD) rats fed compositionally different diets were monitored over 114 weeks to determine whether rats fed ad libitum (AL) or diet restricted (DR) followed normal growth parameters. A second objective was to evaluate the usefulness of the American Institutes of Nutrition's AIN-93M (maintenance formulation) diet for aging and DR studies. METHODS Rats were fed NIH-31 cereal-based diet AL, or a vitamin-fortified modification of the NIH-31 diet at 10, 25, or 40% DR. Other SD rats were fed AIN-93M diet AL or 31% DR; daily nutrient intake and growth response were reported. RESULTS At all intervals up to 36 weeks of age, rats fed AL the NIH-31 diet consumed significantly (p<0.001) more than rats fed AL the AIN-93M diet, and required more diet per unit of gain than AIN-93M AL rats. However, body weight (BW) gain in rats AL-fed the AIN-93M diet demonstrated that energy components were more efficiently metabolized than in those fed the NIH-31 diet. Whereas diet restriction decreased BW, the rate of maturation, i.e., the rate of reaching a mature BW, increased as intake level decreased. Growth response showed all growth curves were normal, but intake level effects on mature BW and maturation rate differed significantly (p<0.001). Curves for rats AL- and DR-fed the AIN-93M diets were similar to those of rats AL- and DR-fed NIH-31 diet formulations, suggesting that diets adequately met growth requirements and supported normal growth parameters of male SD rats when fed AL or DR. CONCLUSIONS A modification in the AIN-93M energy components to reduce total calories and an evaluation of other nutrient profiles could improve its usefulness as a maintenance and aging diet.