Common Terms Used in Animal Feeding and Nutrition
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 a feed in treated silage) plus the true proteins which 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 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 (contains starch and sugars). These two components are successfully separated by using the 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%) 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 then 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.
Digestible Dry Matter (DDM) or Dry Matter Digestibility (DMD): 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)]
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 horse feed. However, given that FE only partially accounts for the energy losses 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): 48-hour in vitro digestible fraction of Neutral Detergent Fiber (NDF) expressed as percentage of dry matter content of a feed sample. Contrast with Neutral Detergent Fiber Digestiblity (NDFD).
Distillers Grains: Distillers grains are residual grains or byproducts remaining after the starch from grains has been the 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 US. 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: indicate 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): 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 DMILegume is expressed as % of BW, and NDF (Neutral Detergent Fiber) and NDFD (48-hour in vitro NDF digestibility) are expressed as % of DM 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 effected by the condition of the animal (e.g., age, body weight, pregnancy status, and 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.).