Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2001
Publication Date: 1/1/2002
Citation: Duffy,P.H., Lewis,S.M., Mayhugh,M.A., Thorn,B.T., McCracken,A., Reeves,P.G., Blakely,S.A., Casciano,D.A., Feuers,R.J. 2002. Effect of the AIN-93M purified diet and dietary restriction on survival in the Sprague-Dawley rat: Implications for chronic studies. Journal of Nutrition. 132:101-107.
Interpretive Summary: In studies that use rats and mice as models to test the nutrient quality of food, and the toxic effects and/or the safety of food chemicals and drugs, it is very important that the animals receive diets that are nutritionally balanced as well as allow the animal to live out their normal lifespan while consuming the diet. In 1993, the American Institute of Nutrition sponsored the development of the AIN-93G and AIN-93M diets to be used in such studies. These diets were developed at the USDA ARS Grand Forks Human Nutrition Research Center, Grand Forks, ND, and contain semi-purified ingredients so they could be produced with less variability than natural ingredient diets, but still maintain adequate growth, maintenance, and reproductive efficiency. Over the ensuing years, they have been tested to determine if they live up to expectations. Recently, the FDA, National Center for Toxicological Research, Jefferson, AR, finished a two year long study to determine if the AIN-93M diet was as good as the standard natural ingredient diet, NIH-31, when fed to the laboratory rat model. The results showed that the survival rate for Sprague-Dawley strain of male rats given free access to the AIN-93M diet was similar to that for similar rats fed the NIH-31 diet (43.3% and 51.7%, respectively). The study indicates that the AIN-93M diet is suitable for long-term feeding studies that use this rat model. More studies will be conducted to improve the AIN-93G and M diets even further.
Technical Abstract: Survival, growth, and dietary intake (DI) variables were monitored in a chronic 114-wk study in which male Sprague-Dawley (SD) rats (National Center for Toxicological Research Colony) were fed the American Institutes of Nutrition's AIN-93M purified diet ad libitum (AL), or an amount reduced by 31% of total AL intake. The main objectives were to ascertain the suitability of the AIN-93M diet for use in chronic bioassays and to determine if dietary restriction (DR) increases longevity of rats fed this diet containing casein as compared to the use of mixed protein sources in the NIH-31 cereal-based diet. Body, liver, brain, brain/body, spleen, thymus, and kidney weights, body length, and body density were decreased by DR, whereas, testis weight and skull length were not altered by DR. Significant age effects were found for body, brain, brain/body, liver, and testis weights and body density. Survival rates for the AL and 31% DR groups were 43.3% and 57.5%, respectively. Survival curves were not significantly different. The survival rate for AL rats fed the AIN-93M diet was similar to that for AL rats fed the NIH-31 diet (43.3% and 51.7%, respectively). However, the survival rate for 31% DR rats fed the AIN-93M diet was significantly lower than 25% DR rats fed the NIH-31 diet (57.5% and 87.5%, respectively); both groups had similar body weights. Nutritional components in the NIH-31 diet, which are missing and/or reduced in the AIN- 93M diet, may interact with DR mechanisms to increase 114-wk survival. Study results indicate that the AIN-93M diet is suitable for chronic rodent studies.