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Commodities: Field Crops: Forages

Common Terms Used in Animal Feeding and Nutrition

Glossary: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


National Research Council (NRC): A scientific body in the U.S. under the National Academy of Sciences that has regularly published sets of tables of each nutrient required by an animal for body maintenance, growth, production, and rebreeding performance based on the latest available research.

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. It is based on the fact that each of the major chemical components of a sample has characteristic near infrared light absorption (and hence reflectance) patterns which is used to differentiate one component from the others. NIRS has been proved as a rapid and low-cost method to analyze forage and grain crops for their nutritive value. Generally speaking, relative to conventional “wet chemistry” procedures, this method is much faster in determining forage nutritional content and is less expensive. It is very precise but the accuracy of NIRS is dependent on appropriate calibration with the results of “wet chemistry”.

Net Energy (NE): the amount of feed energy actually available for animal maintenance, growth and production. Conceptually, total NE is the portion of metabolizable energy (ME) remaining after the energy expended in body heat (or “heat increment of feeding”) is deducted, i.e.:

  • NE = ME - heat increment of feeding

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.

It should be kept in mind that most published NE values for feeds are not measured values; rather they are estimated (or converted) from the DE system, so they are subject to the same set of limitations as in estimation of digestibility in the DE system. Nevertheless the NE system is quite useful for ration formulation and evaluation.

Net Energy for Gain or Growth (NEg): An estimate of the energy in a feed used for body weight gain once maintenance is achieved.

Net Energy for Lactation (NEl): An estimate of the energy in a feed used for maintenance plus milk production during lactation.

Net Energy for Maintenance (NEm): An estimate of the energy in a feed used to keep an animal in energy equilibrium, neither gaining weight nor losing weight.

Neutral Detergent Fiber (NDF): 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 enables 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 microorganisms in animals with either a rumen (e.g., cattle, goats, or sheep) or a hide-gut fermention (e.g., horses, rabbits, guinea pigs) as part of their digestive tract.

NDF concentration is negatively correlated with dry matter intake (i.e., as NDF in the forage increases, animals will consume less forage). As a result, NDF is often used in formulas to predict the dry matter intake.

Neutral Detergent Fiber Digestibility (NDFD): The 48-hour in vitro digestible fraction of NDF expressed as percentage of Neutral Detergent Fiber (NDF) content of a feed sample.

Neutral Detergent Solubles (NDS):  The NDS represents all forms of ingredients in a feed sample which are soluble in neutral detergent solution. That means it represents everything that is not NDF. Usually 98% of the NDS is assumed to be digestible.

Nitrate (NO3): Nitrate concentrations in forages and other feeds are generally low. When the rate of nitrate uptake (e.g., uptake per day) by the plant from the soil exceeds its rate of conversion to protein, nitrates will accumulate in plants. Nitrates can accumulate in the forage crop due to excessive nitrogen fertilization and excessive moisture stress or other factors that limit growth. Excessive concentrations of nitrate in the animal’s diet can induce nitrate toxicosis in the animal (e.g., reduced weight gain, failure to rebreed, weakness, staggering, and, in severe cases, death of the animal). A qualitative check called the “diphenylamine test” can be used to screen forages for potential harm from nitrate. These types of test kit are available in most County Extension offices. The concentration of nitrate that is considered toxic varies considerably from one class of animal to another. More specific guidelines on preventing or mitigating nitrate toxicity in forages can be found in Extension Circular C915 “Nitrate Toxicity”.

The amounts of nitrate in the animal’s water should also be considered. The University of Georgia recommends testing the nitrate content in the forage and water provided to your livestock, if elevated levels of nitrate are suspected.

Nitrogen Free Neutral Detergent Fiber (NDFn): Nitrogen free NDF (NDFn) is estimated as:

  • NDFn = NDF – NDFICP (Neutral Detergent Fiber Insoluble Crude Protein)
  • Also estimated as, NDFn = NDF × 0.93.

Non-fibrous Carbohydrate (NFC) or Neutral Detergent Soluble Carbohydrates (NDSC): NFC or NDSC represents all forms of digestible carbohydrates which are solubilized after boiling a feed sample in neutral detergent solution. These are indeed all forms of non-cell wall carbohydrates and include starch, sugar, pectin, and fermentation acids which are digestible and serve as energy sources for the animal. Because NFC includes some other digestible compounds in addition to starch and sugars included in NSC, NFC generally shows a higher value than non-structural carbohydrate (NSC) on the feed analysis report. NFC is calculated from the following equation:

  • NFC% = 100% – [CP% + (NDF% –NDFICP%) + EE% + Ash%]

where EE% is the ether extract% or Fat%.

Non-protein Nitrogen (NPN): nitrogen in a feed sample that is not in the form of protein but can be used by the microbial population in the rumen or gastro-intestinal tract to synthesize amino acids and proteins. Common forms of NPN are urea and ammonia.

Non-structural carbohydrate (NSC): simple carbohydrates, such as starches and sugars, stored inside the cell that can be rapidly and easily digested by the animal. Hence, NSC is considered to serve as a readily available energy source.

Nutrient: an element, compound, or group of compounds that are required and/or used for nourishment and performance of an animal. Common groups of animal nutrients are: carbohydrates (or energy), proteins, fats, minerals, vitamins, and water. It is an interesting side note that the fiber fractions do not directly qualify as measure of nutrients. They fail the direct test of nutritive entities. However, they are correlated with digestibility and energy so they do have indirect nutritive value.

Nutrient Requirements: 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 (but, does not include a safety margin in ration formulation).

Nutritive value (NV): Protein, mineral, and energy composition, availability of energy, and efficiency of energy utilization in a feed.