Should the AIN-93 Rodent Diet Formulas be Revised?

The early 20th century saw the replacement of wild-caught rats with purpose-bred rat strains, beginning with the Wistar rat developed by Helen Dean King in 1906 (1), to serve as homogenous, standardized animal models for human physiology.Although most nutrient requirements were not yet known, and nutrient standards were not completed until the 1960s, rodent diets were commonly grain-based and supplemented with a variety of products to produce adequate growth without signs of deficiency.But even in the 1940s, purified diets were reported in scientific journals (2).These diets, however, were nutritionally inadequate, especially with regards to their vitamin and mineral contents, were inaccurately and insufficiently reported, and were often imprecise in their formulation (3).These discrepancies contributed to poor reproducibility and erroneous conclusions not only in nutritional studies, but also in toxicological, oncological, and behavioral research.This situation prompted the formation of a committee of the AIN (predecessor to the ASN) to develop the first widely accepted open-source formula diet for both rats and mice, which provided the precise quantity of purified ingredients that met all nutrient requirements known at that time (4).To correct reported problems, the diet was soon modified to AIN-76A with the addition of more vitamin K and an antioxidant (5).The latter report included a discussion about alternatives to sucrose as the carbohydrate and included anecdotal reports suggesting that dietary fiber might be inadequate, but made no specific recommendations.The AIN-76A formula became the gold standard for feeding rats and mice, but within 13 years, discussion began on modification of the AIN-76A recipe to add trace minerals (6).Along with those deliberations, all nutrients were reassessed, which eventually resulted in publication of the AIN-93G (growth) and AIN-93M (adult maintenance) formulas (7-9).[While the work that resulted in the 1993 publications in The Journal of Nutrition was ongoing, the fourth edition of Nutrient Requirements of Laboratory Animals, published in 1995 by the NRC, was being prepared (10).There were informal discussions taking place between the members of that NRC subcommittee and the authors of the Journal of Nutrition publications that turned out to be beneficial to both parties.The committees that produced these reportsThe authors reported no funding received for this study.