The National Research Council (NRC) was organized by the National Academy of Sciences, "a private, nonprofit, self-prepetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare" for the purpose of furthering knowledge and advising the federal government.
The NRC Committee on Animal Nutrition produced the current 5th revised edition of Nutrient Requirements of Horses in 1989 (referred to as "NRC"). Though there have been many advances in equine nutrition since then, this edition is still the basis for most equine nutrition reference.
The NRC outlines most of the known nutrient requirements for horses by weight, age, work level and reproductive status. It includes tables listing the minimum requirements, discussions of each of the nutrients listed, and maximum tolerance levels. The requirements stated in the NRC "...indicate the minimum amounts needed to sustain normal health, production, and performance of horses" based on research available at the time. As it may be some time before the new requirements are made available, the current edition is still a valuable resource. It can be ordered (softcover) online or viewed in it's entirety for free at National Adademy Press .
Kentucky Equine Research (KER) was established in 1989 and has hosted numerous nutrition conferences since then. The proceedings of these conferences have been compiled in three volumes, Advances in Equine Nutrition I, II & III, plus the Proceedings of the 2004 Equine Nutrition Conference that includes discussion of the "New Horse NRC. These volumes present much of the equine nutritional research that has occurred since the current NRC was published and provide a source of more recent information for determining what to recommend in the equine diet. Many of the Proceedings articles can be viewed online at Kentucky Equine Research in the KER library, or the volumes can be purchased there.