What is a Vitamin Requirement – How is it Defined?

One hundred years ago this was an easy question to answer:  enough of a given vitamin to prevent or cure a deficiency disease, such as night blindness, rickets, scurvy, or beri-beri.  Or, in a quote attributed to Vitamin C researcher Albert Szent-Gyorgyi: “a vitamin is a substance that makes you ill if you don’t eat it.”

Today, published guidelines such as Nutrient Requirements of Dairy Cattle, 8th Revised Edition, NASEM, 2021, are established by an expert panel, and several new terms for vitamin requirements were introduced.  Borrowing from (human) nutrient standards and Dietary Reference Intake definitions, the dairy expert panel adapted several terms and concepts new to the livestock industry:

Estimated Average Requirement (EAR): the average daily nutrient intake estimated to meet the requirements of half of the healthy individuals in a given life stage and gender group—in other words, the middle of the bell curve.  Example: a 650 kg cow producing 40 kg milk requires 150 g of calcium per day as an estimated average requirement—this is enough to support the lactation and maintain body reserves in half of the population of cows weighing 650 kg (1430 lb).

Recommended Dietary Allowance (RDA): RDA is defined as the daily nutrient intake sufficient to meet the requirements of 97-98% of healthy individuals, or EAR plus 2 standard deviations (usually EAR times 1.2).  There are no recommended dietary allowances for vitamins in the NASEM 2021 dairy document, due to lack of adequate population and statistical data.

Adequate Intake (AI): the average daily nutrient intake that a panel of experts has determined which should meet or exceed the requirements of a specific group, based on limited data or when the RDA can’t be estimated.  Most vitamin recommendations are expressed as AI’s due to lack of adequate statistical data to determine an average requirement. As an example, 2000 IU of vitamin E in research outperformed 1000 IU in a mastitis study, which outperformed unsupplemented controls—resulting in an AI for transition cows = 2000 IU/hd/d: the lowest intake of vitamin E which would support a given production requirement.1

Response:  another important category for vitamins, a “response” is defined as a production response which occurs when X amount of nutrient is fed, even though there may be no deficiency involved (as an example, a recent meta-analysis shows 1.7 kg of milk response when 20 mg biotin was fed to lactating dairy cows). 

The DSM Optimum Vitamin Nutrition (OVN®) concept picks up where AI’s and Responses leave off.  For example, many nutritionists use multipliers (based on expected processing losses or herd variability concerns) when determining supplemental vitamin levels against an Adequate Intake.  These multipliers often exceed 1.2 times the estimated AI, and can range from 1.5-2 X the minimum requirement in an industry segment.  But what happens during heat stress (this creates an oxidative environment often accompanied by intake depression), mycotoxin challenges, or pasture feeding, where intakes can be variable or nonexistent, or when the need for antioxidants is increased?  OVN guidelines take into account performance challenges or special applications, such as egg hatchability, meat quality or immune support. Over time, the animal industry and academic perspective on vitamin requirements has changed from “avoid deficiencies” to “support current industry practices and objectives.”  The DSM recommendation in all species segments is to “Check and Adjust. For more sustainable farming.”  Watch for new OVN 2022 guidelines for aquaculture, ruminants, swine and poultry.


  1. Weiss et al, 1997. Effect of Vitamin E supplementation in diets with a low concentration of Selenium on mammary gland health of dairy cows.  J Dairy Sci, 80:1728-1737

Published on

15 August 2022



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