Revising Equine Nutrient Requirements

At the 2004 Kentucky Equine Nutrition Conference for Feed Manufacturers, held Oct. 18-19 in Lexington, Ky., there was a strong focus on the upcoming revision of the National Research Council's (NRC) publication Nutrient Requirements of Horses, used by many as the Bible of equine nutrition. Last published in 1989, this text is currently slated for re-publication in late 2005 or early 2006.

Several presentations discussed the revision process, led off by the University of Kentucky’s Laurie Lawrence, PhD, professor of animal science and the new chairman of the NRC's subcommittee on horse nutrition. She began by describing the origins and mission of the National Academy of Sciences (of which the NRC is a part), and its relationship to the Board on Agriculture and Natural Resources (BANR).

After listing the committee members and detailing their work to date on this project, Lawrence described the project's mission as follows: "To perform comprehensive analysis of recent research on feeding horses, horse nutrition, nutrient requirements, and physiological/environmental factors affecting requirements."

She added that the committee is inviting comments on the target audience of the NRC publication (i.e., horse owners vs. nutritionists), the book's format, length, and any other suggestions. The committee is also considering excerpting the book to create short pamphlets or booklets of specific information (such as body condition scoring or forage evaluation). "We're really interested in your input on this," she said to the nutritionists at the conference.

Comments from the public can be submitted by visiting; click the "Current Projects" link on the left side and enter "horses" in the search box, then click the link for “BANR-O-03-08-A, Nutrient Requirements of Horses.” One can also submit comments directly to the committee members, who are:

  • Laurie M. Lawrence, PhD
  • Nadia F. Cymbaluk, DVM, MS
  • David W. Freeman, MS, PhD
  • Raymond J. Geor, BVSc, MVSc, PhD, Dipl. ACVIM
  • Patricia M. Graham-Thiers, MS, PhD
  • Annette C. Longland, BSc, PhD
  • Brian D. Nielsen, MS, PhD
  • Paul D. Siciliano, MS, PhD
  • Donald R. Topliff, MS, PhD
  • Eduardo V. Valdes, BSc, MS, PhD
  • Robert J. Van Saun, MS, DVM, PhD

A third option is to send comments to American Feed Industry Association (AFIA) Nutrition Council specialty committee chairman Randy Robbins, PhD (Manager of Business Development at Hi-Pro Feeds) at

The Feed Industry Perspective
Robbins discussed feed industry views on the NRC revision of guidelines for feeding horses, stating that the AFIA is "a vehicle by which the equine NRC subcommittee can access information from industry sources.

"Why is the feed industry interested in completion of the new NRC book?" he asked the audience. "Because it sets standards used for laws and regulations, and its interpretations by various boards and courts form the foundation for government and legal actions (by agencies such as the FDA and EPA)." For example, he stated that in Texas, no vitamin C is allowed in feeds because the NRC publication lists no requirement for it.

These regulations, he said, can concern what is considered feed ingredients vs. drugs (and thus what is allowed in animal feeds), as well as environmental management of animal production facilities. While nutrition and environment management might seem unrelated, consider the impact that animal waste, a direct result of feed, has on soil and water quality. 

"Aside from nitrogen and phosphorus, the EPA is concerned about all microminerals and how they affect soil nutrient profiles and runoff," he added.

Robbins said the feed industry can and will help the NRC subcommittee by providing resources and information on ingredients used in their feeds, nutrient profiles of those ingredients, and manufacturing processes.

Applying the Science
Joe Pagan, PhD, owner of Kentucky Equine Research (KER), discussed practical applications of the nutrition information in the NRC publication, as well as explaining some of the research behind the 1989 publication.

"We have to give these guys (owners and producers) recommendations with or without exact science, because they're out there managing the animals," he said. "How should a feed manufacturer use the NRC requirements to formulate feed recommendations? The first step in ration evaluation is to describe the horse(s) being fed. The second is to define nutrient recommendations, as opposed to requirements.

"It is crucial to differentiate between recommendations and requirements when evaluating nutrient adequacy of a ration," he went on. "The 1989 NRC gives minimum amounts of nutrients needed to sustain health, performance, etc. A requirement is the minimum amount needed under ideal conditions. A recommendation is a modification of the requirement to account for specific conditions, such as variation in metabolism and production/performance capabilities of individuals, owner expectations, health of the horse, interrelationships among nutrients, variations in nutrient availability of the diet components, breed, discipline, region, environment, etc. This gets more into the art rather than the science."

Pagan quoted a 2001 study that found the NRC nutrient requirements for companion animals are "sufficient to prevent lesions or growth retardation in 50% of animals." In comparison, he said, the Association of American Feed Control Officials recommends 1.3-2 times the corresponding NRC values for dogs and cats, and human RDAs (recommended daily allowances) are two standard deviations above mean minimum requirements, thus encompassing the needs of 98% of the population.

For horses, KER has developed recommendations for several nutrients that are multiples of the NRC requirements. Pagan presented these as follows:


Class of Horse








1.1 x NRC values

1.1 x NRC values

1.0 x NRC values

0.75-0.9 x NRC values

1.0 x NRC values

























Pagan also noted that "The 1989 NRC does not provide recommendations about the level of fiber required in the horse's ration other than to offer the rule of thumb that horses should be fed at least 1% of their body weight per day of good-quality roughage or be given access to pasture for sufficient time to consume at least 1% of body weight as dry matter per day. The 1989 NRC discusses different sources of energy for the horse, but does not provide recommendations for either safe or optimal levels of each source in the horse's ration. This is an area of prime importance for all classes of horses and should be a major focus of research in the future."

Regarding ration balancing, Pagan opined that doing this based on concentrations of the total diet (as is done in the NRC) rather than amounts is "totally incomprehensible for the end user, and makes assumptions about the forage to grain ratio and overall energy density of the feed. Additionally, what’s confusing is that when people think of nutrient concentrations, they’re generally thinking only of the concentrations in the grain they buy, rather than that of the whole ration including forage." He added that the NRC's chloride and forage recommendations were good common sense guidelines, but aren't based on controlled studies.

He likened nutrient balancing to driving a car: "If you keep it on the road (in the optimal nutrient area), you're fine. If you get off the pavement (into the high or low marginal nutrient areas), you can usually get back on the road. But if you get in the ditch (where a nutrient is deficient or toxic), then you have a wreck!"

And how does one know what the marginal, deficient, or toxic levels of nutrients are? It depends on the nutrient; all of the nutrients in a horses' diet will never match recommended levels exactly, and the horse's tolerance for nutrient levels outside that target varies with the nutrient. This is where a nutritionist can help you identify any problem areas in your horse's diet.

"Determining nutrient requirements is hard work," he commented. "That's why we don't have a lot of these answers." He went on to describe ways of evaluating energy consumption and utilization/availability of other nutrients, along with several studies and their results.

"In conclusion, NRC requirements for horses are of little practical value for evaluating rations unless they are expressed as recommended daily allowances with acceptable ranges of nutrient intake," Pagan stated. "The next revision of the NRC will hopefully include more of this type of information."

Making Nutrient Composition Tables Relevant
"The best rations are based on feed analyses," said Paul Sirois, BS, MS, of Dairy One Forage Lab in Ithaca, N.Y. "Nutrient composition tables (which give average nutrient compositions of various feedstuffs and are often cited as the basis for equine rations) should be used only as a secondary source in the absence of analytical data. To provide the best information, tables should incorporate data from a variety of contemporary sources."

Sirois recommended that the NRC subcommittee find as many data sources as possible for the nutrient composition tables in the new publication, stating that this would "improve robustness (of the data), give a better idea of nutrient variability, and increase confidence in published values. Noting that there are now 189 feed testing labs that are part of the Association of American Feed Control Officials (AAFCO), he observed, "There are more nutrient composition data available now than ever before. The committee should contact as many labs as possible."

Why is this important? Sirois argued that the 1989 publication included information on far too few samples of each feed, resulting in some published values not really reflecting the norm for that nutrient. "For alfalfa, the NRC used 63 samples. Dairy One has 51,389 sample results they could use. For timothy, they only used 15 samples. We have 15,097. The 1989 NRC did right by publishing the n (number of samples) and standard deviations for the feeds. But the number of observations is way too low. There are only one to four observations for many plants. That's terrible! To validate the tables, one must account for nutrient variation."

He took exception to many of the published mineral values for the same reason, citing the example of copper content in grass hays, which he said is two to three times the normal levels for grasses.

Another problem with the NRC, he said, is that it was too specific in its forage classification, which was based on species and stage of maturity. He stated that most pastures and hays are a mix of species, and stage of maturity is rarely reported or reported incorrectly. For example, the NRC classifies later-maturity forages as full bloom, mature, or late bloom; Sirois noted that many use these terms interchangeably, but the NRC considers them all to be different. Thus, Dairy One has moved to a system of classifying forages as simply legume, mix (mostly legume), mix (mostly grass), and grass.

"It's pretty easy to pick the right one," he commented.

In closing, Sirois made the following comments:

  • "With more sources of data, it (a nutrient table) is more robust and more representative, which equals more confidence in the data.
  • "There is greater variation in feedstuffs than is currently documented (in the NRC publication).
  • "Don't let purity (i.e., splitting a forage into seven stages of maturity) stand in the way of practicality (i.e., how can you ensure that forages are always classified at the correct stage with this many choices?).
  • "The livestock industry would be best served by the development of an easily expandable, comprehensive, web-based library of feed values (currently each species' industry has its own libraries)."

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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