Acid Detergent Fiber (ADF)

The highly indigestible portion of forage that includes lignin, cellulose, silica and insoluble forms of nitrogen, but not hemicellulose.  Forages with higher ADF are lower in digestible energy (in fact ADF is used to calculate the energy value of forages).  During laboratory analysis, ADF is the residue remaining after boiling a forage sample in acid detergent solution.

Acid Detergent Insoluble Crude Protein (ADICP)

ADICP is the insoluble protein fraction remaining in the acid detergent fiber residue of a feed sample.  It is the component of protein that is unavailable to the horse.  This parameter is also reported as acid detergent insoluble preotien (ADIP), acid detergent insoluble nitrogen (ADIN) or acid detergent fiber protein (ADFP).  It is typically expressed as a percent of crude protein, but sometimes on a dry matter basis or both.

Anti-Quality Factors

These are not normally measured in typical forage analysis.  Apart from nutrients, forages may contain various harmful compounds that can adversely affect animal performance and cause sickness or even death.  These compounds can include tannins, nitrates, alkaloids, cyanoglycosides, estrogens, yeast, molds and mycotoxins.  The occurrence and/or severity of these factors depends on the forage and weed species present, season, environmental conditions, geographical region and sensitivity of the animal.

Amino Acids

The building blocks from which proteins are made.  There are 20 standard amino acids required to form proteins (actually 21 – selenocysteine is considered the 21st amino acid as it is required by all mammals).  Amino acids are used to synthesize proteins and other biomolecules.  They can also be broken down and used to produce glucose through gluconeogenesis.  This results in the nitrogen being removed from the amino acid.  The body needs to detoxify this nitrogen, it does so in the liver by turning ammonia (free form of nitrogen) into urea, which is then excreted.

Ascorbic Acid (C)

The only functional role of vitamin C categorically established is its ability to prevent and/or cure scurvy.  In this role, however, it affects to some extent every body function.  For example, normal development of cartilage, bone, and dentine depends on an adequate supply of vitamin C.  In addition, the basement membrane lining the capillaries, the “intracellular cement” holding together the endothelial cells, and the scar tissue responsible for wound healing all require the presence of vitamin C for their formation and maintenance.  Ascorbic acid is an antioxidant, cofactor of hydroxylating enzymes involved in synthesis of collagen, carnitine, norepinephrine.  Horses can produce endogenous vitamin C, there is no evidence supplementation is needed.


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

As-fed Basis

Feed analyses typically report results on an as-fed basis and dry matter basis.  All feeds contain some level of water, which is typically designated as moisture.  This will vary based on the type of feed.  For example, ensiled forages and fresh pasture will contain high levels of water/moisture, 65 and 75 percent, respectively.  Whereas, dry hay and common feed ingredients are typically only 10 to 12 percent moisture.  The nutrient concentrations listed on all commercially available feeds are reported on an as-fed basis.  It is important if entering values for nutrient concentrations of feeds or forages that you are using appropriate values.

Biotin (B7)

Biotin functions in cells covalently bound to enzymes.  These enzymes replenish oxaloacetate for Krebs cycle, necessary for gluconeogenesis; commit acetate units to fatty acid synthesis; provide mechanism for metabolism of some amino acids and odd-numbered chain fatty acids; and allows catabolism of leucine and certain isoprenoid compounds.  Biotin is involved in CO2 transfer reactions; carboxylation reactions.

Calcium (Ca)

Calcium is the most abundant divalent cation of the body, averaging about 1.5% of the total body weight.  Bones and teeth contain about 99% of the calcium.  The other 1% of the body’s calcium is distributed in both intracellular (inside the cell) and extracellular (outside the cell) fluids.  Calcium is a structural component of bones and teeth, role in intracellular and hormonal secretion regulation, muscle contraction, blood clotting, and activation of some enzyme systems


Carbohydrates are biochemical compounds composed only of the elements carbon, hydrogen and oxygen.  They represent the single largest source of energy for horses.  They come in many different forms, which will impact the overall response of the horse to feeding.  Carbohydrates are polymers made of basic sugar units, such as glucose, 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 for the plant are available for more rapid metabolism to supply energy (e.g., sugars, starch and pectin) are referred to as non-structural.  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., cellulose, lignin etc).  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.  It is the most abundant carbohydrate on earth.  Cellulose is an unbranched chain of glucose molecules that are linked together by beta-1,4 bonds.  Mammals do not contain the enzymes necessary to digest cellulose (break the beta-1,4 bonds between glucose molecules), but bacteria do.  The microflora present in the hindgut of a horse are able to digest cellulose, allowing the horse to derive significant amounts of energy from cellulose, an example of the symbiosis between the horse and resident bacterial population.  Cellulose is not generally measured in lab analysis, but can be estimated as follows:

Cellulose = ADF – (ADL + Ash), where ADF is acid detergent fiber and ADL is acid detergent lignin

Chloride (Cl)

Chloride is the most abundant anion in the extracellular fluid.  Approximately 88% of chloride is found in extracellular fluid, and just 12% is intracellular.  Its negative charge neutralize the positive charge of sodium ions with which it is usually associated.  In this respect, it is of great importance in the maintenance of electrolyte balance.  Chloride has important functions in addition to its role as a major electrolyte.  It is require for the formation of gastric hydrochloric acid, secreted along with protons from the parietal cells of the stomach.  Also, it acts as the exchange anion in the red blood cell.  Chloride functions as a major anion, maintains pH balance, enzyme activation, and is a component of gastric hydrochloric acid


Choline is an essential material for building and maintaining cell structure. It is a constituent of lecithins which are fatty substances (lipids) with one of the three fatty acid molecules replaced by choline which is joined to the glycerol part of the molecule through a phosphoric acid linkage.  The free choline pools from which the neurotransmitter acetylcholine is synthesized are maintained through several mechanisms, one of which is the enzymatic hydrolysis of lecithin and sphingomyelin.  Choline can be synthesized in liver providing there is a sufficient supply of methionine.  Choline plays an essential role in fat metabolism in the liver.  It functions by preventing abnormal accumulations of fat by converting excess fat into lecithin or by increasing the utilization of fatty acids in the liver.  Choline is involved in neurotransmission, fatty acid metabolism in liver, and cell structure

Chromium (Cr)

No Cr-dependent enzyme has been identified.  However, Cr is an essential trace element due to its function as a cofactor involved in activation of insulin.  The biological action of chromium is believed to be due to its complexing with nicotinic acid and amino acids to form the organic compound glucose tolerance factor (GTF).  GTF is thought to initiate the disulfide bridging between insulin and the insulin receptor.  The effectiveness of insulin is greater in the presence of chromium than in its absence.  Thus the primary function of GTF is to potentiate insulin action, thereby affecting cellular glucose uptake, and intracellular carbohydrate and lipid metabolism.

Cobalamin (B12)

Vitamin B12 is considered a generic term for a group of compounds called corrinoids because of their corrin nucleus.  The corrin is a marocyclic ring made of four reduced pyrrole rings linked together.  The corrin of vitamin B12 has an atom of cobalt in the center of it.  Cobalamin is involved in methylation of homocysteine to methionine; conversion of methylmalonyl CoA to succinyl CoA

Cobalt (Co)

Cobalt must be supplied in the diet of monogastric animal species and humans in its active form, vitamin B12.  When these species receive adequate dietary vitamin B12 there is no convincing evidence of a requirement for or benefit from dietary Co.  Cobalt is, however, a dietary essential for ruminants; ruminal, microogranisms incorporate Co into vitamin B12.  The only known function of Co is its participation in metabolism as a component of vitamin B12.


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.

Copper (Cu)

In most animal species, Cu is poorly absorbed; the extent of absorption is influenced by its chemical form and by a substantial number of interactions with other dietary factors.  Dietary phytates, high levels of Ca, S, Fe, Zn, Cd, or Mo reduce absorption.  Generally, not more than 5 to 10% of the Cu in the diet is absorbed by adult animals, while young animals may absorb 15 to 30%.  Copper is required for cellular respiration, bone formation, proper cardiac function, connective tissue development, myelination of the spinal cord, keratinization, and tissue pigmentation.  Copper serves as an essential catalytic co-factor of several physiologically important metalloenzymes. It is surpassed only by Zn in the number of enzymes which it activates.  At least three Cu enzymes appear to have a role in antioxidant defence.  These are the widely distributed intracellular and extracellular superoxide dismutases (SODs), extracellular ceruplasmin, and intracellular Cu thioneins.  Due to the redox activity of Cu, this metal ion readily participates in the generation of hydroxyl radical, which damages nucleic acids, proteins, and membranes.  Consequently, all cells must establish fine-tuned homeostatic mechanisms to allow cells to accumulate sufficient Cu for essential biochemical reactions, yet prevent the accumulation of Cu ions to toxic levels.

Crude Fiber (CF)

This older proximate method was used to divide carbohydrates into digestible and indigestible fractions.  When the CF content is higher, the energy content of the feed is lower because crude fiber is considered indigestible.  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 ADF.  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.  Therefore, it is still commonly used for analysis of feeds fed to horses.  Crude fiber is still used as the legal measurement of fiber in grains and finished feeds.


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 Energy (DE)

Is the most commonly reported energy value of feedstuffs for horses.  It 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 feces (fecal energy or FE) from the gross intake energy.  DE = GE – FE.  It is important to formulate diets for adequate, but not excessive amounts of DE for individual horses.

In horses, FE only partially accounts for the energy losses during absorption and digestion.  There are considerable energy losses via urine and gases in the process of the utilization of nutrients.  DE may overestimate low quality feeds relative to high quality feeds.  Therefore it is important to monitor condition of the horse and not rely solely on DE values as an assumption of appropriate energy intake.

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 the feed sample.  Note the difference between neutral detergent fiber digestibility (NDFD or NDFd) below.

Distillers Grains

These are the residual grains or byproducts remaining after the starch from grains has been fermented to alcohol.  If limiting starch intake is of interest, these can be excellent alternative feedstuffs, although care must be taken to not feed excessive protein.

Dry Matter (DM)

Dry matter represents everything contained in a feed sample except water (often referred to as moisture in lab analysis).  It is the total weight of feed minus the weight of water in the feed, expressed as a percentage.  As a consequence, the nutrient values on a dry matter basis will always be higher than when reported on an as-fed basis.

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.  As the percent of neutral detergent fiber (NDF) increases in the feed, animals consume less, DMI is less.  The relationship between DMI and NDF content of legumes and grasses has been used to estimate DMI using the following equations which are expressed as grams of forage intake per kilogram of body weight per day.  Simply multiply result by horse’s body weight to get total intake per day expressed in grams.  Divide by 1,000 to express in kilograms.

DMIgrass = 124.55 + 0.155 * %NDF2 – 2.5742 * %NDF

DMILegume = 18.377 – 0.0051 * %NDF2 + 0.3895 * %NDF

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 work, etc.), feed factors (e.g. palatability, balance of the diet, anti-quality factors, etc.) and the feeding environment (e.g. temperature, humidity, access to feed etc.).


Ensiled refers to plant materials preserved by anaerobic fermentation, typically at moisture levels between 55-65 percent.  Ensiled feeds are well accepted by horses, but concerns with botulism, from contamination with dead animals, has limited its wider implementation as a forage preservation method.

Ethanol Soluble Carbohydrates (ESC)

Ethanol soluble carbohydrates are those carbohydrates that can be solubilized and extracted in 80 percent ethanol.  ESC includes primarily monosaccharides and disaccharides (simple sugars).

Ether Extract (or Crude Fat)

(The rest of us call it fat) The portion of the feed that is extracted with ether or similar solvent.  It is a laboratory test to approximate the total or crude fat content of a feed.  This measure of fat also contains some waxes, pigments and other lipids (basically anything soluble in ether), so it is not a measure of true fat, hence the use of the name ether extract. An estimate of the total fat content of feeds estimated using ether extraction.  Crude fat contains true fat (triglycerides), alcohols, waxes, terpenes, steroids, pigments, ester, aldehydes and other lipids.


Chemically, fats are triglycerides of fatty acids.  Fat is rich in energy, containing 2.25-2.8 times the energy found in carbohydrates and protein and it is highly digestible.  It is used primarily to increase the energy density of rations.  Specific fatty acids are essential to normal health and maintenance.

Fatty Acids

Are comprised of a straight hydrocarbon chain terminating with a carboxylic acid group.  Fatty acids are components of more complex lipids (commonly called fat).  They are of vital importance as an energy nutrient, but also in the production of bioactive compounds.  Two fatty acids are considered essential, meaning they must be consumed through the diet, which is otherwise stated as – the animal does not have the ability to synthesize these fatty acids.  The essential fatty acids are linoleic (18:2 n-6) and α-linolenic acid (18:3 n-3), an omega-6 and omega-3 fatty acid, respectively.

The essentiality of the fatty acids linoleic acid and α-linolenic acid is due to the fact that some of the longer, more highly unsaturated fatty acids into which they can be converted are necessary 1) for the formation of cell membranes and 2) as precursors of compounds called eicosanoids.

There are a few different nomenclatures for fatty acids, but the most common designation is given as: x:y n-z where (x=number of carbon atoms):(y=number of double bonds) (n- z=the first carbon where double bond exists counted from the methyl, or omega end of the chain).  For example, α-linolenic acid would be expressed as 18:3 n-3, meaning it is 18 carbons long, with 3 double bonds, starting at the third carbon when counting from the omega end.

The length of the chains of fatty acids found in foods and body tissues ranges from 4 to about 24 carbon atoms.  They may be saturated (SFA), monosaturated (MUFA, containing one carbon-carbon double bond), or polyunsaturated (PUFA, having two or more carbon-carbon double bonds).

Nutritional interest in the n-3 (omega-3) fatty acids has escalated enormously because of their reported hypolipidemic and antithrombotic effects, which is of particular interest for horses with insulin resistance.  Furthermore, immune system function is impacted by fatty acid composition of the diet.  In very general terms, the omega-6 fatty acids are considered to be pro-inflammatory and the omega-3 anti-inflammatory based on their respective roles in prostaglandin synthesis.

Folic Acid (B9)

Folate and folacin are generic terms for compounds that have similar chemical structures and nutritional properties similar to those of folic acid.  Folic Acid and subsequently dihydrofolate are both reduced by dihyrofolate reductase, a cytosolic enzyme, to generate tetrahydrofolate (THF).  THF accepts one-carbon groups from various degradative reactions in amino acid metabolism.  These THF derivatives then serve as donors of one-carbon units in a variety of synthetic reactions.


Forage refers to plants or plant parts other than the separated grains fed to or grazed.  Forage may be fresh, dry or ensiled.  Examples of each would include: pasture, hay and haylage, respectively.

Gross Energy

Gross energy refers to the total energy in a feed before accounting for losses due to normal digestive, metabolic, and productive functions.  It is determined by measuring the amount of heat produced when a feed is completely oxidized in a bomb calorimeter.

It is not a very useful measure since the gross energy in most common feeds is about the same, but they do not result in similar animal performance.  For example, GE in oat grain = GE in oat straw.


Like cellulose, hemicellulose is a carbohydrate that exists in almost all plant cell walls along with cellulose.  Whereas cellulose is composed only of glucose, hemicellulose is composed of many other sugars (e.g. glucose, xylose, mannose, galactose, arabinose, etc.) in branched polymer arrangement.  As hemicellulose content increases in animal feed, the voluntary feed intake typically decreases.

International Unit (IU)

A standard unit of potency of a biological agent (e.g. vitamin, hormone, antibiotic, etc.); also called a USP unit in the U.S.  Most vitamins are expressed in IU’s, vitamin A & D are often expressed as KIU, the K simply indicates 1,000 units of IU.

In Vitro

In vitro (Latin for “within the glass”) generally refers to the technique of performing a given biological procedure in a controlled environment outside of a living organism.

Iodine (I)

Iodine is unique among the required trace elements in that it is a constituent of the thyroid hormones thyroxine and triiodothryonine.  Iodine deficiency is accepted as the most common cause of preventable mental defects in the world today.  In humans and farm animals, iodine deficiency is one of the most prevalent deficiency diseases, and it occurs in almost every country in the world.  The only known role of iodine is in the synthesis of the thyroid hormones.  Thyroxine contains about 65% iodine.  Thyroid hormones have multiple functions as regulators of cell activity and growth.  They have an active role in thermoregulation, intermediary metabolism, reproduction, growth and development, circulation and muscle function; they control the oxidation rate of all cells.  An increase in thyroid hormone levels results in an increase in the basal metabolic rate.  Selenium deficiency will have a role in the control of thyroid hormone metabolism.  The deiodinating enzyme, which produces most of the circulating T3 is a selenoenzyme with most of the activity occurring the liver, kidney and thyroid.  Selenium also plays an indirect role in the control of thyroid hormone synthesis because it is required by another selenoenzyme, GSH-Px.  In the thyroid, GSH-Px is thought to be the main antioxidant system for neutralizing cytotoxic hydrogen peroxide and its oxidative by-products.  Hydrogen peroxide is produced by the thyroid as a cofactor in thyroid hormone synthesis.  High iodine intake when Se is deficient may initiate thyroid tissue damage as a result of low thyroidal GSH-Px activity during thyroid stimulation.

Iron (Fe)

Over 65% of body iron is found in hemoglobin, up to about 10% is found as myoglobin, about 1% to 3% is found as part of enzymes, and the remaining body iron is found in the blood or in storage.  Iron, a metal, exists in several oxidations states varying from Fe+6 to Fe-2, depending on its chemical environment.  The only states that are stable in the aqueous environment of the body (and in food) are the ferric (Fe+3) and the ferrous (Fe+2) forms.  Necessary component of hemoglobin and myoglobin for oxygen transport and cellular use; facilitates transfer of electrons in electron transport chain


Lignin is a complex carbohydrate compound, a major structural component of mature plants, contained in the fibrous portion of plant stems, leaves, cobs, and hulls.  It is indigestible and hence has a negative impact on cellulose digestibility.  As the lignin content in a feed increases, digestibility of its cellulose decreases, thereby lowering the amount of energy potentially available to the animal.


Lipids are substances found in plants and animal tissues that are insoluble in water, but soluble in benzene or ether.  Lipids include glycolipids, phosphoglycerides, fats, oils, waxes and steroids.


Lysine is an essential amino acid.  It is often thought to be the first limiting amino acid in a typical corn/soybean based diet.  It is the only amino acid that the National Research Council (NRC) has established a requirement for in the horse.  Synthetic forms of lysine are readily available and can be used to fortify diets if lysine content is inadequate.

Manganese (Mn)

At the molecular level, manganese, like other trace elements, can function both as an enzyme activator and as a constituent of metalloenzymes, but the relationship of these functions to the gross physiologic changes observed in manganese deficiency is not well correlated.  In the activation of enzyme-catalyzed reactions, the metal can act by binding to the substrate (such as ATP) or the enzyme directly, with induction of conformational changes.  Enzymes that can be activated by manganese in this manner are numerous and diverse in function.  They include hydrolases, kinases, decarboxylases, and transferases.  The activity of most of these enzymes is not, however, affected by a manganese deficiency, largely because the activation is not manganese specific.  Essential for normal brain function; role in enzyme systems, collagen formation, bone growth, urea formation, fatty acid and cholesterol synthesis, and protein digestion.

Maximum Tolerable Levels

The level or concentration at which a substance in the diet can be fed long term without inducing clinical toxicity, disease or metabolic malfunction.  Used most commonly for vitamins and minerals.  These levels should, in no way, be construed as an approachable level when formulating rations.

Macro Minerals

Macro minerals are the elements present in the animal body in relatively larger amounts than micro minerals.  Therefore, macro minerals are required in relatively large amounts, generally in gram (g) quantities, often expressed as a percent of the total diet.  Macro minerals interact with each other and must be supplied in proper quantities and ratios to maintain appropriate animal function.  The seven essential macro minerals are: calcium (Ca), phosphorus (P), sodium (Na), magnesium (Mg), potassium (K), sulfur (S), and chlorine (Cl).

Magnesium (Mg)

Magnesium as a cation in the body ranks fourth in overall abundance, but intracellularly it is second only to potassium.  Approximately 60% of magnesium is in bone and remaining 40% in extracellular fluids and soft tissues.  Magnesium is a component of bones; role in nerve impulse transmission, protein synthesis, enzyme activation (in glycolysis and many ATP-dependent reactions).

Megacalorie (Mcal)

The calorie was first defined as a unit of heat.  By technical definition a calorie is the approximate amount of energy needed to raise the temperature of one gram of water by one degree Celsius.  A kilocalorie (kcal) would be the energy required to raise one kilogram of water by one degree Celsius.  And so on, a Megacalorie is the amount of energy required to raise one metric tonne of water by one degree Celsius.

In horse nutrition it is the unit of energy used in the measure of energy contained in a feedstuff or to define an animal’s energy requirement.  In human nutrition, they refer to Calories, referred to as the large calorie or more appropriately kilocalorie.

Metabolizable Energy (ME)

Metabolizable energy equals the gross feed energy minus the energy lost in the feces, urine, and gaseous product of digestion.

o   ME = GE – FE (energy in feces) – (energy in urine) – (energy in gases)

This is not often used in horses, as there are limited studies to provide adequate data for the majority of feedstuffs to quantify ME accurately in the horse.


An essential sulfur containing amino acid involved in many vital enzymatic processes.

Micro Minerals

Micro minerals, or trace minerals, are present in animal body tissues in extremely low concentrations. They are nutrients required in small amounts, generally in milligram (mg) or microgram (ug) amounts per day, but play critically important roles in animal nutrition.  There are 10 essential trace minerals recognized in animal nutrition: iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), selenium (Se), cobalt (Co), iodine (I), chromium (Cr), molybdenum (Mo), and nickel (Ni).  Of these, it is rare to supplement Cr, Mo, or Ni, but the rest are normally included in horse feeds or mineral and vitamin premixes.

Milligram per Kilogram (mg/kg)

mg/kg is equivalent to parts per million (ppm).  It is the common unit of concentration representing how many mg of the target substance are present in one kilogram of the sample/feed.


In feed analysis, minerals refers to inorganic feed elements essential for life.


Animals having a single compartment or simple stomach system (e.g. pig, horse).  Contrast with rumen and ruminants.


Mycotoxins can be toxic to animals, and are produced on plants by fungi, particularly during weather stress during the growing or harvest seasons or during feed storage (e.g. vomitoxin, zearalenone, aflatoxin, and T-2).

National Research Council (NRC)

The NRC is a scientific body in North America under the National Academy of Sciences that regularly publishes sets of tables of each nutrient required by an animal for body maintenance, growth, production and rebreeding performance based on the latest available research.

Nutrient Requirements of Horses is currently in its 6th edition, published in 2007.

Near Infrared Reflectance Spectroscopy (NIRS) or Near Infrared Analysis (NIRA)

The NIRS method of analysis is a computerized instrumental method for rapidly and reproducibly measuring the chemical composition of samples with little or no sample preparation other than drying and grinding.  As opposed to conventional “wet chemistry” methods, NIRS measures the reflections of near infrared light instead of chemicals to determine protein, fiber, energy and other variables of interest.  Mineral analysis in mixed feed samples should always be done with ‘wet chemistry’ and not NIR.

Net Energy

Net energy refers to the amount of feed energy actually available for animal maintenances, growth and work.  Total NE is the portion of metabolizable energy (ME) remaining after the energy expended in body heat (or “heat increment of feeding”) is deducted.

NE is further partitioned into the net energy necessary for maintenance (no gain or loss of body weight), growth (or gain in body weight) and lactation (production of milk).  The NE requirements for maintenance, growth and lactation are denoted by NEm, NEg, and NEl, respectively.

Most published NE values are not measured values, they are estimated from the DE system, so they are subject to the same set of limitations as an estimation of digestibility in the DE system.

An estimate of energy in a feed used for body weight gain once maintenance is achieved.
An estimate of the energy in a feed used to maintenance plus milk production during lactation.
An estimate of the energy in a feed used to keep an animal in energy equilibrium, neither gaining, nor losing weight

Neutral Detergent Fiber (NDF)

NDF is the residue or insoluble fraction left after boiling a feed sample in neutral detergent solution.  The NDF contains plant cell wall components except for some pectins.  The NDF is considered a close estimate of the total fiber constituents of feedstuffs since it measures cellulose, hemicellulose, lignin, silica, tannins and cutins.  The hemicellulose, cellulose and lignin represent the fibrous bulk of the forage.  Because they give the plant rigidity and enable it to support itself as it grows, these three components are classified as structural carbohydrates.  Though lignin is indigestible, hemicellulose and cellulose can be (in varying degrees) digested by microogranisms in animals with either a rumen (e.g. cattle, goats or sheep) or hind-gut fermentation (e.g. horses, rabbits, guinea pigs) as part of their digestive tract.

Niacin (B3)

The term niacin is considered a generic term for nicotinic acid and nicotinamide (also called niacinamide).  Approximately 200 enzymes, primarily dehydrogenases, require nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP).  Most of these enzymes function reversibly.  Although NAD and NADP are very similar and undergo reversible reduction in the same way, their functions are quite different in the cell.  The major role of NADH, formed from NAD, is to transfer electrons from metabolic intermediates through the electron transport chain, thereby producing adenosine triphosphate (ATP).  NAPH, in contrast, acts as a reducing agent in many biosynthetic pathways such as fatty acid synthesis.

Non-Fibrous Carbohydrate (NFC)

NFC% = 100% – (CP% + (NDF% – NDFIP%) + EE% + Ash%)

Represents all the carbohydrates that are not part of the structure of the plant otherwise known as non-cell-wall carbohydrates.  NFC is not measured directly, but calculated (above) by subtraction of the other components in the plant.  There are a couple issues with NFC 1) laboratory methods for measuring NDF differ, some now use sodium sulfite method to extract NDF, which also removes the NDFIP fraction, so there is no need to subtract the NDFIP from NDF and 2) analytical errors are compounded into the NFC.

Non-Structural Carbohydrates (NSC)

Enzymatic determination of the sugars, starches and organic acids contained in feed.  Similar to non-fiber carbohydrate, but key difference is that NSC is measured, where NFC is calculated.  NFC includes pectin, which the NSC does not.  This can result in large difference in the two values for feeds high in pectin.  See also NFC

Non-Protein Nitrogen (NPN)

NPN refers to nitrogen in a feed sample that is not in the form of protein.  Common forms of NPN are urea and ammonia.  It is important to never feed urea or ammonia to horses.  It is used in ruminant diets as it can be used to synthesize amino acids by the microbial population of the rumen, but is toxic to horses.

Nutrient Requirements

Nutrient requirement refers to the minimum amounts of nutrients (energy, protein, fat , minerals and vitamins) necessary to meet an animal’s real needs for maintenance, growth, reproduction, lactation or work.  This does not include a safety margin in ration formulation.  Given the multiple sources of error when formulating a ration from feed analysis to what the horse actually consumes, it is important to always formulate with some level of margin of safety.  It can also be stated that minimum nutrient requirements are set based on the avoidance of any overt clinical symptoms of deficiency and may not necessarily provide an optimum feeding level.

Pantothenic Acid (B5)

One of the primary functions of pantothenic acid relates to its role as a component of CoA.  The synthesis of CoA requires pantothenic acid, cysteine, and ATP.  As a component of CoA, pantothenic acid becomes essential for production energy from carbohydrate, fat and protein.

Parts per Million (ppm)

Unit of measure commonly used to state micro mineral concentrations in feed.  Same as milligrams/kilogram (mg/kg).


Pectin is an intercellular (occurs between cells) polysaccharide (carbohydrate) that functions as a cellular glue.  The main source of difference between the measurement of NSC and calculation of NFC.

Phosphorus (P)

Among the inorganic elements, phosphorus is second only to calcium in abundance in the body.  Approximately 85% of the body’s phosphorus is in the skeleton, with the remainder associated with organic substances of soft tissue.  Phosphorus is a structural component of bone, teeth, cell membranes, phospholipids, nucleic acids, nucleotide coenzymes, ATP-ADP phosphate energy transferring system in cells, participates in regulation of pH and osmotic pressure of intracellular fluids.

Potassium (K)

98% of the body’s potassium is intracellular, making it the major intracellular fluid cation.  Potassium influences the contractility of smooth, skeletal and cardiac muscle, and profoundly affects the excitability of nerve tissue.  It is also important in maintaining electrolyte and pH balance.


Depending on geographical location premix can have different meanings.  In general, a premix only contains the mineral and vitamin portion of the diet and is added to the rest of the diet to provide a completely balanced feed with all the necessary minerals and vitamins.  In contrast many supplements available for horses, may not contain a complete or appropriate balance of minerals and vitamins.  The term premix generally indicates it contains the complete profile of minerals and vitamins required.

A macro premix contains all the macro minerals, along with all the micro minerals and vitamins.  Whereas, a micro premix (very low inclusion rate in the total diet) would only contain the micro minerals and vitamins.  Sometimes called a vitamin trace mineral pak (VTM).

Protein or Crude Protein (CP)

Often referred to as crude protein because it is a measure of total nitrogen, not the actual protein content of a feed.  The total nitrogen content of a feed is multiplied by 6.25 based on the assumption that true protein contains 16% nitrogen.  Proteins are made up of amino acids.

Pyridoxine (B6)

Pyridoxine may be converted into pyridoxine phosphate (PNP) within the intestinal cells, likewise pyridoxal is typically converted pyridoxal phosphate (PLP).  PN & PNP may be converted to PLP in the liver.  PLP is the main form of the vitamin found in the blood.  Other forms of the vitamin, especially PL also may be present in the blood.  The coenzyme form of vitamin B6 is associated with a vast number of enzymes, the majority of which are involved in amino acid metabolism.

Relative Feed Value (RFV)

Relative feed value is a forage quality term that is used to rank forages, according to their overall nutritive value.  This ranking is relative to the typical nutritive value of full bloom alfalfa hay (mature).  Full bloom alfalfa hay, containing 41 percent ADF and 53 percent NDF on a dry basis, has a RFV of 100.  Though RFV has no units, it compares the potential of two or more like forages on the basis of energy intake.  Thus, it serves as an index of forage quality for comparing forage lots.  Such a single suitable parameter is useful for practical forage pricing and marketing.


One of the limitations of the RFV system is that it assumes constant relationships between NDF and intake, and between ADF and digestibility.  However, two forages can have identical NDF levels but very different digestibilities and, therefore, intakes.  This often results in RFV of high-quality forages being underestimated because their intake is underestimated.

Relative Forage Quality (RFQ)

RFQ is a forage quality term that is similar to RFV in that it is used to rank forages according to their relative nutritive value.  RFQ shares many of the properties of RVF (e.g. its basis of comparison is 100, the typical nutritive value of full bloom alfalfa hay; it has no units; it compares the potential of two or more like forages on the basis of energy intake; it serves as a useful index of forage quality for comparing forage lots; and it is very useful for practical pricing and marketing of forage lots).  Unlike RFV, RFQ takes into account digestible fiber (derived from ruminants)

RFQ is based on intake and true TDN instead of DDM.  This makes RFQ a better predictor of forage quality than RFV.  This is because RFQ accounts for NDF digestibility (NDFd) and the contribution of other nutrient fractions when calculating TDN, rather than calculating DDM based merely on ADF.

The equations used to calculate DMI and TDN for legumes and legume/grass mixtures are specific to those forages and are different from those used to calculate DMI and TDN for warm and cool season grasses.  Proper identification of forage type will therefore be essential before RFQ calculation

Riboflavin (B2)

Most of the riboflavin in tissues is first converted to one of its coenzyme forms.  Synthesis of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) appear to be under hormonal regulation.  Hormones shown to be particularly important in this regulation are ACTH, aldosterone, and the thyroid hormones, all of which accelerate the conversion of riboflavin into its coenzyme forms apparently by increasing the activity of flavokinase.  FMN and FAD function as cofactors for a wide variety of oxidative enzyme systems and remain bound to the enzymes during the oxidation-reduction reactions.  Flavins can act as oxidizing agents because of their ability to accept a pair of hydrogen atoms


Roughage refers to bulky and coarse feed high in fiber (greater than 18 percent crude fiber) but lower in energy than most concentrates.  For example, forage, hay, silage, and haylage are sometimes called roughage.


The rumen is the foregut (or forestomach) of ruminant animals such as cattle, sheep and goats.  The rumen is large, hollow muscular organ that is the site of most of the fiber digestion that occurs in ruminant animals.  This digestion is largely performed by microogranisms (bacteria, protozoa and fungi) that inhabit the rumen.  Similar to the digestion process in the hindgut of a horse.

Selenium (Se)

Perhaps more than any other essential trace element, selenium varies greatly in its soil concentration throughout the regions of the world.  This, in turn, relates directly to its concentration in food plants.  This heterogeneous distribution has had scientific benefit in that it has provided a clear correlation between those selenium-poor regions of the world and the incidence of disease associated with selenium deficiency.  Selenium compounds are generally absorbed very efficiently in monogastrics.  Selenocysteine and selenomethionine (organic selenium compounds) are almost 100% absorbed.  In comparison, selenite (common form used in most horse feeds) has a lower apparent absorption ranging from 30% to about 60%.  Selenium performs its functions mainly through selenoproteins.  Approximately 30 to 35 selenoproteins can be detected in mammalian tissues.  The biochemical reactions catalyzed by mammalian selenoproteins fall into three broad categories: 1) antioxidant defense systems, 2) thyroid hormone metabolism and 3) redox control of cell reactions.  Selenium protect cells against destruction by hydrogen peroxide and free radicals.


The 21st amino acid.  It is structurally similar to cysteine, but selenium replaces the sulfur in the amino acid.  The higher reduction potential of selenium versus sulfur makes selenoproteins much more effective antioxidants.  The production of many selenoproteins (potent antioxidants) is dependent on the amount of selenium available, therefore it is imperative to maintain adequate selenium status to maintain immune function and antioxidant status.


Silage refers to the feed preserved by an anaerobic fermentation process (e.g. corn silage and haylage) in which lactic acid and volatile fatty acids (produced by fermentation) lower the pH of the silage.  The low pH preserves the silage.  See Ensiled.

Sodium (Na)

Approximately 30% of the sodium in the body is located on the surface of bone crystals.  From that site, it can be released into the bloodstream should low serum sodium levels develop (hyponatremia).  Sodium functions as an electrolyte; role in water, pH, and electrolyte regulation, nerve transmission, muscle contraction.

Structural Carbohydrates

Structural carbohydrates are the complex carbohydrates that form the plant cell wall and include cellulose, hemicellulose, lignin and pectin.  They are typically measured in the laboratory as neutral detergent fiber (NDF).

Sulfur (S)

Component of sulfur containing amino acids, thiamin, biotin and lipoic acid


A supplement feed or feed mixture is used to improve the nutritional value of the ration complementing the nutrients in the base feed.  A supplement is rich in one or more of protein, energy, vitamins or minerals.  In combination with the base feeds, produces a more complete feed, with the goal of meeting the animal’s nutrient requirements.

Thiamin (B1)

At the cellular level, thiamin plays essential roles in: 1) energy transformation; 2) synthesis of pentoses and NADPH (a coenzyme form of niacin, nicotinamide adenine dinucleotide phosphate in a reduced form); and 3) membrane and nerve conduction.  Thiamin diphosphate (TDP) functions as a coenzyme necessary for the oxidative decarboxylation of both pyruvate and alpha-ketoglutarate.  These reactions are instrumental in generating ATP.  Inhibition of these decarboxylation reactions prevents synthesis of ATP and acetyl CoA needed for the synthesis of, for example, fatty acids, cholesterol and other important compounds and results in the accumulation of pyruvate, lactate, and α-ketoglutarate in the blood.

Total Digestible Nutrients (TDN)

TDN is a measure of the energy value in feedstuff.  The term TDN has its origins in an older system of measuring available energy in feeds and very hard to measure directly.  Today, reported TDN values are calculated, not measured values.  Formulas for calculating TDN originally were based on ADF and frequently varied by region and the nutritionist doing the calculation.

Though TDN is a widely used measure of energy, it is not without its weaknesses.  The most significant issue with TDN is that it does not account for additional energy losses, particularly heat increment and, to some extent, gaseous losses.  Consequently, TDN is known to over-estimate the energy value of roughages compared to grains.


Toxicity refers to the extent to which a substance can exert a poisonous effect on animals.


Vitamins are organic compounds that typically function as parts of enzyme systems essential for many metabolic functions.

Vitamin A

The term vitamin A is used to refer to retinol and retinal. Retinoic acid is a metabolite of retinal.  The term provitmain A refers to beta-carotene and other carotenoids that can be converted into retinol.  Vitamin A is recognized as being essential for vision, and for systemic functions including cellular differentiation, growth, reproduction, bone development, and the immune system.

Vitamin D

Calcitriol, 1,25-(OH)2D3, is considered the active form of vitamin D and functions like a steroid hormone.  Initially the target tissues of the vitamin were believed to be limited to the intestine, bone and kidney.  The presence of specific receptors for the hormone in many other tissues, however, supports that calcitriol acts in a wide variety of tissues, including the heart, brain, and stomach.  Calcitriol plays a role in the parathyroid hormone (PTH)-directed homeostasis of blood calcium concentrations, which impacts several tissues including the intestine, bone and kidney.  Hypocalcemia stimulates secretion of PTH from the parathyroid gland.  The PTH, in turn stimulates 1-hydroxylase in the kidney such that 25-OH D3 is converted to calcitriol.  Calcitriol then acts alone or with PTH on its target tissues, causing serum calcium and phosphorus concentrations to rise.

Vitamin E

Vitamin E includes eight compounds synthesized by plants.  These compounds fall into two classes: the tocols, which have saturated side chains, and the tocotrienols (also called trienols), which have unsaturated side chains.  All compounds are designated as alpha, beta, gamma, or delta, and possess characteristic biological activity.  Another compound, all-rac α-tocopheryl acetate, with vitamin E activity is used in fortification of feed.  The principal function of vitamin E is the maintenance of membrane integrity in body cells.  The mechanism by which vitamin E functions to protect the membranes from destruction is through its ability to prevent the oxidation (peroxidation) of unsaturated fatty acids contained in the phospholipids of the cellular membranes

Vitamin K

Several compounds possess vitamin K activity; these compounds all have a 2-methyl 1,4-naphthoquinone ring.  The naturally occurring forms of vitamin K are phylloquinone (K1), isolated from plants, and menaquinones (K2) synthesized by bacteria.  Menadione (K3) is not found naturally but is a common synthetic form of vitamin K that must be alkylated for activity.  Vitamin K is necessary for the posttranslational carboxylation of specific glutamic acid residues to form γ-carboxyglutamate on 4 of 13 factors required for the normal coagulation of blood.  The 4 vitamin K-dependent factors include factors II (pro-thrombin), VII, IX, and X.

Water-Soluble Carbohydrates (WSC)

WSCs are the carbohydrates that can be solubilized and extracted in water.  WSC’s include monosaccharides, disaccharides and some short chain polysaccharides, mainly fructans, which are a major storage carbohydrate in some cool season grasses (e.g. timothy).

“Wet Chemistry” Analysis

Wet chemistry is a term that collectively refers to a number scientific techniques involving direct analyses with solvents, acidic or basic solutions, other chemicals and other traditional laboratory methods used to analyze feed samples.

Zinc (Zn)

Zinc can exist in several different valence states, but it is almost universally found as the divalent ion (Zn+2).  Zinc is found in all organs and tissues (primarily intracellularly) and in body fluids.  Most of the zinc is found in bone, liver, kidney, muscle and skin.  The primary role of Zn in the body appears to be related to its association with enzymes and proteins both as part of the molecule and as an activator.  There are over one thousand known proteins associated with Zn.  Role in energy metabolism, protein synthesis, collagen and keratin formation, carbon dioxide elimination, sexual maturation, taste and smell functions.