photo of cows feeding on hay in pasture

Prepared by:

  • Uttam Saha, Program Coordinator, Feed and Environmental Water Laboratory
  • Leticia Sonon, Program Coordinator, Soil, Plant, and Water Laboratory
  • Dennis Hancock, Assistant Professor, Extension Forage Specialist
  • Nicholas Hill, Professor, Crop and Soil Sciences
  • Lawton Stewart, Assistant Professor, Extension Beef Specialist
  • Gary Heusner, Professor, Extension Equine Specialist
  • David E. Kissel, Professor and Director, Agricultural and Environmental Services Laboratories

The largest operating cost in a livestock production enterprise is the feed bill. To keep this cost low, one must supply the right amount of feed to the animals. Overfeeding is wasteful. Underfeeding will decrease animal performance and profitability. Therefore, proper animal feeding and nutrition are crucial to the profitability of the livestock enterprise.

Laboratory analyses of the composition of feed or forage are used to assess their nutritive value (Figure 1). A typical feed analysis includes measurements of some important quality attributes or parameters (e.g., crude protein, fiber, digestibility, etc.) used to define nutritive value. Other parameters are analyzed under some special circumstances. For example, acid detergent insoluble crude protein (ADICP) is usually only measured if heat damage to the feed is suspected.

Flow chart that shows how samples are analyzed in a laboratory. Figure 1. A schematic that describes the partitioning of organic and mineral components in a feed and forage sample.

Many of the parameters included in laboratory reports are calculated or estimated from measured feed quality attributes. For example, digestible energy, total digestible nutrients and intake potential are all estimated from the concentration of the various fiber components and the relationship between them. The University of Georgia?s Feed and Environmental Water Laboratory (FEWL) is located in Athens and dedicated to providing objective analyses of feeds and forages. This is in line with UGA?s mission as a land-grant university to provide unbiased interpretations, recommendations and pertinent educational materials to enhance the profitability and sustainability of livestock production systems in the state.

The purpose of this publication is to serve as an educational reference and resource to those who are interested in animal feeding and nutrition. Our primary objective is to list the common terms used when discussing animal feeding so that one might be better informed when consulting with county Extension personnel, feed salesmen, animal nutritionists, veterinarians, feed laboratory managers and other industry professionals. This listing will also be helpful when reading articles on animal feeding and nutrition, feed analysis reports or tags associated with feeds sold in the market.

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Acid Detergent Fiber (ADF)

The fibrous component represents the least digestible fiber portion of forage or other roughage. This highly indigestible part of forage includes lignin, cellulose, silica and insoluble forms of nitrogen but not hemicellulose. Forages with higher ADF are lower in digestible energy than forages with lower ADF, which means that as the ADF level increases, digestible energy levels decrease. During laboratory analysis, ADF is the residue remaining after boiling a forage sample in acid detergent solution. ADF is often used to calculate digestibility, total digestible nutrients (TDN) and/or net energy for lactation (NEl).

Acid Detergent Insoluble Crude Protein (ADICP) or Acid Detergent Fiber-Crude Protein (ADFCP)

ADICP (or ADFCP) is the insoluble protein fraction remaining in the acid detergent fiber residue of a feed sample. ADICP escapes ruminal breakdown and represents the portion of the protein that is not degradable and is therefore unavailable to the animal. It also contains any heat-damaged protein that may result from heating during storage or processing. In this case, a portion of the protein reacts with carbohydrates (fiber) to form an indigestible complex, rendering it unavailable for digestion. This parameter is also reported as acid detergent insoluble protein (ADIP), acid detergent insoluble nitrogen (ADIN) or acid detergent fiber protein (ADFP). It is expressed as a percent of crude protein. It is an adequate estimate of heat-damaged protein in forage feeds but not in non-forage feeds (Nakamura et al., 1994).


Fungal or mold growth in or on foods and feed can result in the production of many different types of toxic biochemicals. As a group, these toxic substances are commonly called mycotoxins. The term aflatoxins refers to a particular group of mycotoxins produced by some species of the genus Aspergillus. There are four major aflatoxins named B1, B2, G1, G2 plus two additional metabolic products known as M1 and M2 that are of significance as direct contaminants of foods and feeds.

Fungal (or mold) growth and aflatoxin contamination are the consequence of interactions among the fungi, the host (foods or feeds) and the environment. On a standing crop, aflatoxin contamination of peanuts and corn is favored by high temperatures, prolonged drought conditions and high insect activity, while postharvest production of aflatoxins on corn and peanuts is favored by higher water content, warm temperatures and high humidity. Forages are generally not analyzed for aflatoxins but in some situations (e.g., corn or sorghum silage that is at risk) this analysis may be warranted.

The presence of aflatoxins in feeds, forages and foods is an important anti-quality factor and is associated with various diseases in livestock, domestic animals and humans that are broadly termed aflatoxicosis. Aflatoxicosis is primarily a hepatic (liver) disease. Liver damage, decreased reproductive performance, reduced milk or egg production, embryonic death, teratogenicity (birth defects), tumors and suppressed immune system function are caused by aflatoxins even when low levels are consumed.

The FDA?s (Food and Drug Administration) action level for human food is 20 ppb total aflatoxins, with the exception of milk, which has an action level of 0.5 ppb for aflatoxin M1. The FDA action level for most feeds is also 20 ppb (Table 1).

Table 1. FDA action levels for aflatoxins§
Commodity Action level
(µg/kg or ppb)
All products, except milk, designated for humans 20
Milk 0.5
Corn for immature animals and dairy cattle 20
Corn for breeding beef cattle, swine and mature poultry 100
Corn for finishing swine 200
Corn for beef cattle 300
Cottonseed meal (as a feed ingredient) 300
All feedstuff other than corn 20
§According to compliance policy guides 7120.26, 7106.10 and 7126.33.

If the level of aflatoxins in forage is higher than the action level, it may be fed in combination with other feeds containing low levels of or no aflatoxins.

Amino Acids

A class of nitrogen-containing molecules containing an amine group, a carboxylic acid group and a side chain that varies between different amino acids. Amino acids are the building blocks from which protein is made in the body. There are 20 known standard amino acids forming various proteins. When taken up into the body in the diet, the 20 standard amino acids are either used to synthesize proteins and other biomolecules or broken down into urea and carbon dioxide. Of the 20 standard amino acids, eight are called essential amino acids and the other 12 are called non-essential amino acids. Animals (including humans) cannot synthesize the essential amino acids from other compounds at the level needed for normal growth, so they must be obtained from food (hence they are called essential amino acids).

Anti-quality Factors

Apart from nutrients, forages may contain various harmful compounds that can adversely affect animal performance and cause sickness or even death. These compounds are called anti-quality factors and include tannins, nitrates, alkaloids, cyanoglycosides, estrogens and mycotoxins. The occurrence and/or severity of these factors depend on the forage and weed species present, season, environmental conditions and sensitivity of the animal. High-quality forages should be free from harmful levels of anti-quality components.


The residue containing inorganic mineral elements of a feed sample, determined in a laboratory by burning the sample at a high temperature (removing the organic matter) and weighing the residue (i.e., ash).

As-fed Basis

Feed analyses reports often state results based on the feed?s natural state (i.e., including water) and/or on a dry matter basis. The term “As-fed Basis” is used to alert the reader that the analytical results of a feed sample are based on its natural state including water. That means it is affected by the sample?s moisture level before drying. This may also be referred to by the terms “As-is Basis” or “As-received Basis.” When comparing two or more analyses, it is generally best to utilize the data from the “Dry Matter Basis” rather than the “As-fed Basis” unless you are mixing a ration for feeding.

Balanced Ration

Complete feed formulated to provide a specific animal species and class with appropriate amounts of all nutrients required for maintenance and a given level of performance.


Botulism is a muscle-paralyzing disease caused by botulinum toxin, a potent neurotoxin produced mainly by the bacterium Clostridium botulinum and also by a few strains of C. baratii and C. butyricum. Clostridium botulinum is an anaerobic (can only grow under anaerobic conditions) bacterium that usually grows when the pH of the growing medium is greater than 4.6.

Botulism can result from the ingestion of the toxin or the growth of C. botulinum on anaerobic food/feed tissues. Seven types of botulinum toxin, designated A through G, have been identified. Types A, B, E and F cause illness in humans. Type C is the most common cause of botulism in animals. Type D is sometimes seen in cattle and dogs, and type B can occur in horses. Types A and E are found occasionally in mink and birds. Type G rarely causes disease, although a few cases have been seen in humans. All types of botulinum toxin produce the same disease; however, the toxin type is important if anti-toxin is used for treatment.

The toxins come from a variety of sources. Decaying vegetable matter (e.g., grass, hay, grain, spoiled silage) and carcasses can cause botulism in animals. Ruminants may inadvertently be fed hay or silage contaminated by carcasses of birds or mammals that may contain the toxin. Horses usually ingest the toxin in contaminated forage.

Botulinum toxins are large proteins that can be easily denatured. Toxins exposed to sunlight are inactivated within one to three hours. Botulinum can also be inactivated by 0.1% sodium hypochlorite, 0.1 M NaOH, heating to 80°C for 30 minutes or 100°C for 10 minutes. Chlorine and other disinfectants can destroy the toxins in water.

By-pass Protein

The portion of intake protein that has a slow rate of degradability in the rumen. It is fed so that it may escape digestion in the rumen, reach the lower gastrointestinal (GI) tract essentially intact and be digested directly in the small intestine as it would be in non-ruminants. This can provide a balance of amino acids unaltered by microbial digestion and synthesis. By-pass protein is also known as undegradable intake protein (UIP), rumen undegradable protein (RUP) or escape protein.


Carbohydrates are biochemical compounds composed only of the elements carbon, hydrogen and oxygen, and are the main source of energy for animals. Animals get the majority of their required energy from the carbohydrates in feeds. Carbohydrates are polymers made of basic sugar units, such as glucose (the most abundant), fructose, galactose, etc. The two major classes of carbohydrates in plants are known as non-structural and structural. Those that serve as storage and energy reserves and that are available for more rapid metabolism to supply energy (e.g., sugars, starch, and pectin) are referred to as non-structural carbohydrates. Those carbohydrate fractions that are not used for energy storage and provide fiber and anatomical features for rigidity and even water transport are known as structural carbohydrates (e.g., fibrous cellulose and hemi-cellulose). Non-structural carbohydrates are more available for energy metabolism than the structural carbohydrates.


Cellulose is a major structural carbohydrate that is present in plant cell walls. Cellulose is an unbranched chain of 7,000 to 15,000 glucose molecules that are linked together by ß-1,4 bonds. Cellulose is a major part of the structural fiber in forages and can be utilized by microorganisms in the rumen. When utilizing the chemistry associated with the Van Soest Detergent Fiber Fractions, cellulose is estimated as follows:

  • Cellulose = ADF ? (ADL + Ash)

Where ADF is acid detergent fiber and ADL is acid detergent lignin.


Concentrates refer to animal feeds that are rich in energy and/or protein but low in fiber, such as corn, soybean meal, oats, wheat, molasses, etc.

Crude Fat

Crude fat is an estimate of the total fat content of feeds taken from older collection of methods known as proximate methodology. The crude fat is estimated using ether extraction. Crude fat contains true fat (triglycerides) as well as alcohols, waxes, terpenes, steroids, pigments, ester, aldehydes and other lipids. See Ether Extract and Fat.

Crude Fiber (CF)

This older proximate method was used to divide carbohydrates into digestible and indigestible fractions. When CF content is higher, the energy content of the feed is lower because crude fiber is considered indigestible. Measuring crude fiber was one part of the original system of analyzing the “digestible” fraction in feedstuffs. This method uses sequential acid and alkali extraction. It was developed by Henneberg and Sttohmann during the 1860s at the Weende Experiment Station in Germany, and is often referred to as the Weende System of proximate analysis. The CF extract was once used as a standard analysis for fibrous parts or the indigestible portion of carbohydrates in feeds. However, some of these substances are partially digestible by microorganisms in the rumen. Crude fiber accounts for most of the cellulose but only a portion of the lignin and no ash, so it underestimates true fiber and is less than acid detergent fiber (ADF). Thus, CF is not a good indicator of digestibility in ruminant animals, and the use of this parameter in feeds for ruminants is declining.

Even though CF is not a very useful parameter for quantifying forage fiber where lignin content is substantial, the CF is a reasonable estimate of the fiber in grains because of their low lignin content. Thus, it is still commonly used for analysis of feeds for non-ruminants or monogastric animals (i.e., those that do not have a chambered stomach or rumen; for example, horses and pigs). Crude fiber is still used today as the legal measurement of fiber in grains and finished feeds. See Acid Detergent Fiber (ADF) and Neutral Detergent Fiber (NDF) for contrast.  

Crude Protein (CP)

Proteins are organic compounds composed of building blocks called amino acids. They are a major component of vital organs, tissue, muscle, hair, skin, milk and enzymes. Protein is required on a daily basis for maintenance, lactation, growth and reproduction.

The crude protein content of a feed sample represents the total nitrogen (N) in the diet, which includes not only true protein but also non-protein nitrogen (e.g., urea and ammonia in a feed; nitrate is not included in non-protein nitrogen). Because N is an integral part of any amino acid, non-protein nitrogen has the potential to be utilized for protein synthesis by rumen microorganisms. In laboratory analysis, total N present in a feed sample is first determined and then the total amount of protein is calculated by multiplying the total N by a factor. This factor is 6.25 for forages because leaf and stem tissue proteins generally contain 16 percent nitrogen, or one part nitrogen to 6.25 parts protein. For seeds, this factor is different (e.g., 5.70 for wheat and 5.90 for other cereal grains). Unless otherwise stated, protein values given in lab reports, feed tables and feed tags are crude protein. 

Because the protein content of forages, silages or grains used in animal feeding are sometimes inadequate to meet the needs of the animal class, protein supplements become essential. Consequently, analysis for total protein or crude protein in a feed sample is important.

Crude protein in feeds for ruminants can be further fractionated according to their rate of breakdown in the rumen, as discussed below for neutral detergent fiber insoluble crude protein (NDFICP) and discussed previously for acid detergent fiber insoluble crude protein (ADFICP).

No doubt, CP is an important indicator of the protein content of a forage crop, and even estimates of non-protein nitrogen are important in evaluating nutritive value. However, it is a false perception that protein is always the most limiting nutrient in the animal?s diet and CP is the ultimate measure of a forage quality. In fact, the energy value of forages is often the most limiting attribute for meeting an animal?s requirements in most forage-based feeding. An overemphasis on CP may cause one to fail to pay due attention to meeting energy requirements. Furthermore, CP is merely an estimate of nitrogen content (N, % × 6.25 = CP, %) and must be considered in context of plant maturity, species, fertilization rate and many other characteristics. For example, a high nitrate concentration in the forage will result in an artificially high CP level.

Degradable Intake Protein (DIP)

The DIP, also called Rumen Degradable Protein (RDP), represents the portion of intake crude protein (CP) that can be digested or degraded to ammonia and amino acids in the rumen by microbes. This fraction of CP consists of non-protein nitrogen (e.g., urea and ammonia in treated silage) plus the true proteins that are soluble and those having intermediate ruminal degradability. They are used to synthesize microbial protein in the rumen. The RDP or DIP is expressed as a percentage of CP, where DIP = NPN + Soluble True Protein + True Protein of Intermediate Degradability.

Detergent Fiber Analysis

Since crude fiber (CF) has been found to have an unsatisfactory relationship with animal performance, it has limited value in ruminant nutrition. Most feed analysis laboratories do not use the proximate analysis system (of which CF was a part) and have replaced it with the Van Soest detergent fiber analysis system. The technique of using detergents to separate digestible and indigestible parts of plant tissues was originally proposed by Van Soest in 1963. The concept behind the detergent fiber analysis is that plant cell substances can be divided into less digestible cell walls (made of hemicellulose, cellulose and lignin) and the highly digestible cell contents (containing starch and sugars). These two components are successfully separated by using two different detergent systems:

  • A neutral detergent solution of sodium-lauryl sulfate (C12H25NaO4S) in disodium ethylenediaminetetraacetate (C10H14N2Na2O8) and sodium borate (Na2B4O7) with pH =7 .0 (Van Soest, 1963a); and
  • An acid detergent solution of cetyl-trimethyl-ammonium-bromide (C19H42BrN) in 1N sulfuric acid (Van Soest, 1963b; Van Soest and Wine, 1967).

In a sequential analysis, the feed sample is initially boiled in the neutral detergent solution to separate the neutral detergent soluble fraction (cell contents) from the neutral detergent insoluble fraction (cell walls). The cell contents are highly digestible (about 98 percent) and include various sugars, starches, pectins and other soluble carbohydrates, proteins, non-protein nitrogenous compounds, lipids, water-soluble minerals and vitamins. The remaining dry matter is estimated and the proportion gives the neutral detergent fiber (NDF).

In sequential analysis, the NDF is then further fractionated by boiling in the acid detergent solution. Hemicellulose is solubilized during this procedure while lignin and cellulose remain insoluble. The residue remaining after boiling NDF in acid detergent solution is called acid detergent fiber (ADF). Cellulose is then separated (i.e., solubilized) by adding sulfuric acid. Only lignin and acid insoluble ash remain after this step. The residue is then combusted in a furnace, and the difference of the weights before and after ashing yields the amount of lignin that was present in the sample.


  • NDF = Hemicellulose + Cellulose + Lignin + Ash
  • ADF = Cellulose + Lignin + Ash

Hemicellulose, cellulose and lignin are indigestible in non-ruminants, while hemicellulose and cellulose are partially digestible in ruminants. NDF is a good indicator of the "bulk" fiber and has been used to predict feed intake. In contrast, ADF is a good indicator of digestibility (negatively correlated) and thus energy intake.

The detergent fiber analysis system is the most widely accepted method for forage analysis. However, many agencies still base part of their regulations on terms in the proximate. As a result, both methods are used in most laboratories, including the University of Georgia?s Feed and Environmental Water Laboratory.


Digestibility refers to the extent to which a feedstuff is absorbed in the animal body as it passes through an animal?s digestive tract. It varies greatly with the type of feedstuff and type of animal concerned.

Digestible Dry Matter (DDM) or Dry Matter Digestibility (DMD)

DDM (or DMD) is the portion of the dry matter in a feed that is digested by animals at a specified level of feed intake. There is no direct laboratory method for measuring DDM/DMD. It is often estimated by measuring in vitro or in situ digestibility. Both of these analyses are rather expensive and laborious. So, in vitro digestibility is frequently estimated by near infrared reflectance (NIR) analysis and/or estimated from the acid detergent fiber. The DDM can be calculated as follows:

  • %DDM = 88.9 – [0.779 × %ADF (on a dry matter basis)].

Digestible Energy (DE)

Digestible energy provides an indication of the actual amount of energy from a feed that can be available for use by the animal. It is estimated by subtracting energy lost in the feces (fecal energy or FE) from the gross intake energy (GE), (i.e., DE = GE ? FE). Digestible energy is commonly used to evaluate poultry and horse feed. For poultry feed, DE is considered as an appropriate measure of feed quality, because FE is almost the sole form of energy loss during digestion. However, in horses, given that FE only partially accounts for the energy losses (considerable losses also occur via urine and gases) in the process of the utilization of nutrients, DE may over estimate low quality feeds relative to high quality feeds.

Digestible Neutral Detergent Fiber (dNDF)

The 48-hour in vitro digestible fraction of Neutral Detergent Fiber (NDF) is expressed as a percentage of the dry matter content of a feed sample. Contrast with Neutral Detergent Fiber Digestiblity (NDFD) below.

Distillers Grains

Distillers grains are residual grains or byproducts remaining after the starch from grains has been fermented to alcohol. Traditionally, alcohol was produced mainly for beverages by the liquor industry. However, in the last 25 years its use as an alternative fuel has increased significantly. This increased demand has led to the development of ethanol production plants in various places in the U.S. With increasing ethanol production, the opportunity currently exists for using a substantial quantity of distillers grains as feed in livestock industry.

Dry Matter (DM)

Dry matter represents everything contained in a feed sample except water; this includes protein, fiber, fat, minerals, etc. In practice, it is the total weight of feed minus the weight of water in the feed, expressed as a percentage. It is determined by drying the feed sample in an oven until the sample reaches a stable weight. This is normally a simple analysis. However, estimates of the DM of fermented materials such as silage are complicated by the presence of volatile fatty acids. These acids are removed in the drying process but they are part of the dry matter and are digestible. This introduces a variable amount of error. Analysis of the fodder without ensiling provides a more accurate estimate of fiber fractions and digestibility contained in the silage.

Dry Matter Basis

Dry matter basis indicates the nutrient levels in a feed sample based on its dry matter content (i.e., excluding its water content). This is also referred to as “Dry Basis,” “Dry Results” or “Moisture-free Basis.” As there is considerable variation in the water content of forages, excluding the water or expressing the nutrient levels on a dry matter basis eliminates the dilution effect of the water, thereby providing the essential common basis for direct comparison of the nutrient contents across different forages.

Dry Matter Intake (DMI)

Dry matter intake is the amount of (or prediction of the amount of) dry matter consumed by the animal and is a central concept to any discussion of animal nutrition. Typically, intake increases as the digestibility of the forage increases. However, anti-quality components such as tannins and alkaloids in feeds and forages may decrease intake. Scientists have consistently observed that as the percent of neutral detergent fiber (NDF) increases in the feed, animals consume less (i.e., DMI is less). This relationship, along with estimates of NDF digestibility, is used to estimate DMI for grasses and legumes using the following equations:

  • DMIGrass = -2.318 + 0.442 × CP ? 0.0100 × CP2 ? 0.0638 × TDN + 0.000922 × TDN2 + 0.180 × ADF ? 0.00196 × ADF2 ? 0.00529 × CP × ADF

Where: DMIGrass is expressed as % of BW, and CP (Crude Protein), ADF (Acid Detergent Fiber), and TDN (Total Digestible Nutrient) are expressed as % of DM (Moore and Kunkle, 1999).

  • DMILegume = (120 ÷ NDF) + ([{NDFD – 45} x 0.374] ÷ 1350) x 100

Where DMILegume is expressed as % of BW, NDF (Neutral Detergent Fiber) as % of DM, and NDFD (48-hour in vitro NDF digestibility) as % of NDF [Mertens (1987) with NDFD adjustment proposed by Oba and Allen (1999)].

Though these calculations have been proven to provide reasonable estimates of DMI, the estimates are not perfect. Dry matter intake is affected by the condition of the animal (e.g., age, body weight, pregnancy status, level of milk production, etc.), feed factors (e.g., palatability, balance of the diet, anti-quality factors in the feed, etc.) and the feeding environment (e.g., temperature, humidity, etc.).


Ensiled refers to the plant materials preserved by anaerobic fermentation and typically stored in a bag, bunker, wrapped bale or upright silo.

Ethanol Soluble Carbohydrates (ESC)

ESCs are the carbohydrates that can be solubilized and extracted in 80 percent ethanol. ESC includes primarily monosaccharides and disaccharides.

Ether Extract

Ether extract is a portion of dry matter extracted with ether. It is a laboratory test to approximate the total fat (or crude fat) content of a feed and includes some waxes, pigments and other lipids to a minor degree in addition to true fats.


Chemically, fats are “triglycerides of fatty acids” that are a high-density source of energy for animals. Fat is rich in energy; it contain

Status and Revision History
Published on Jun 18, 2010
Published with Full Review on Jun 17, 2013
Published with Full Review on Mar 28, 2017

Uttam K. Saha Program Coordinator, Agricultural & Environmental Services Lab (AESL) Gary Lee Heusner Extension Animal Scientist, Animal & Dairy Science Nicholas S. Hill Professor, Crop & Soil Sciences David E. Kissel Ph.D Professor Emeritus, Agricultural & Environmental Services Lab (AESL) Leticia S Sonon Ph.D Director, Agricultural & Environmental Services Lab (AESL) Dennis Hancock Professor and Extension Agronomist for Forage Crops (Pasture, Hay, and Silage), Crop & Soil Sciences Lawton Stewart Associate Professor and Extension Coordinator, Animal & Dairy Science
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