Feed Analysis Values - Explanation of Terms

Murray Snowdon, P.Ag.

Dry Matter is determined in the lab by oven drying the sample and determining the amount of moisture. "Dry" feeds usually contain between 10 and 15 % moisture, i.e., dry matter levels between 85 and 90 %.

Silages can range between 20 and 70 % dry matter, making analysis for dry matter level crucial from a ration formulation standpoint. Dry matter level can also have serious implications for fermentation characteristics particularly when values fall outside of the 30 to 50 percent range. The dry matter content of many byproduct feeds is also variable and should be verified by lab analysis.

Crude Protein is determined in the lab using the LECO method which combusts the sample at very high temperature and measures the nitrogen in the resulting gas. Crude protein values are called "crude" because they are calculated from the nitrogen level assuming that nitrogen makes up a constant proportion of protein.

Since protein is expensive, subject to large variation and crucial to animal performance, routine lab analysis for this nutrient is important. Since much of the nitrogen in fermented or heavily fertilized feeds is in a nonprotein form, crude protein will not always accurately reflect a feed's true protein content.

Soluble Protein is measured in the lab by determining the amount of protein that is solubilized in a buffer solution. This measurement is an attempt to predict what portion of the protein will be readily soluble in the rumen. A certain amount of this type of protein is required to support microbial growth in the rumen, while too much can elevate blood levels of urea, reduce animal performance and impair reproduction.

Bound Protein is determined by analysing the protein content of the ADF residue under the assumption that this nitrogen is in a bound form and is not available for digestion. Silages that may have heated are the most likely candidates for this analysis. The most common form of expression is bound protein as a percentage of total protein. Since all forages contain some bound protein, there is no cause for concern until a level of about 10 % has been reached.

UIP (undegraded intake protein) or "bypass" protein is not determined in our lab, but can be estimated by looking at crude protein, soluble protein and bound protein. The undegraded fraction is often referred to as "bypass." UIP for an individual feed will change depending upon the physical form of the feed and feeding conditions, being in large part dependant on the time that the feed stays in the rumen.

ADF (acid detergent fibre) is determined by boiling the sample in an acid bath and then weighing the residue. ADF represents the cellulose and lignin content of a feedstuff. ADF can be used to predict the energy value of a feed, forage maturity and ability of a diet to maintain normal rumen function. ADF is the fibre component that replaced the previously used "crude fibre". A high level of ADF is considered a negative quality parameter, usually indicating an over-mature crop.

NDF (neutral detergent fibre) is determined by boiling the sample in a neutral solution and measuring the residue. NDF includes cellulose, lignin and hemicellulose and thus represents all fibre components. It is gaining popularity as a useful ration balancing parameter. Animal intake is often predicted based on NDF content of the diet. Forage NDF cannot be accurately predicted from ADF even within crop species.

Actual measurement of the energy levels in feeds is limited to a very few research situations. Labs doing routine feed analysis, such as the NB Lab usually predict energy using equations based on the feed. s fibre (ADF) level. Following are explanations of the energy terms supplied by the NB Lab, and an explanation of them.

(a) TDN (Total Digestible Nutrients). This antiquated energy term has remained popular in part because it provides numbers between 1 and 100 that are easy to relate to. TDN is roughly equivalent to digestible energy, but is expressed as a percentage, rather than in calories. Because of the nature of the calculation, feeds containing high levels of fat can have TDN levels greater than 100.

(b) NE (Net Energy for lactation). This energy value is the most commonly used energy term in North America for lactating cow diets.

(c) NEm and NEg. These two terms describe the energy value of a feed and recognize the difference between energy use for maintenance and growth. These values are commonly used in formulating diets for growing beef or growing dairy cattle.

Fat is determined by ether extraction. This measurement usually pertains to fats and oils, but because ether also extracts compounds such as wax the term ether extract is sometimes used to describe this fraction. When other methods which measure only fat and oil are utilized, the term lipid may be used.

Fats are very concentrated sources of energy and can play an important role in the diets of highly productive animals. Fat analysis is not a routine one for most feeds, but can be important when dealing with oilseeds or high fat byproducts such as french fries.

Macro-Minerals - calcium, phosphorus, magnesium and potassium levels are determined using an ICP (Inductively Coupled Plasma Emission) unit which heats the atoms of the sample and measures the light emitted as they cool to determine the level of the various minerals.

Dietary requirements of these minerals are measured as a percent of diet, as opposed to the trace minerals (copper, zinc etc.) which are measured in parts per million or milligrams per kilogram of diet. Forages in particular, have wide ranging levels of all of these nutrients. Even on one farm, forage mineral variability is high, due to different species and harvest dates and wide ranges in field fertility. If lab analysis values are not available, or if inventory control of forages is poor, one is forced to balance diets for the lowest mineral level anticipated.

In the case of a nutrient such as calcium, overfeeding is not expensive. However, with an expensive nutrient such as phosphorus, routine lab analysis that allows smaller safety margins can result in significant feed cost savings. Minimizing nutrient wastage in animal diets is also important from an environmental standpoint.

With the exception of corn silage, forage-based diets do not usually call for potassium supplementation. Potassium analysis is often conducted when dry dairy cow diets are being formulated for a specific balance of anions/cations. Since potassium levels are so variable, the use of "textbook" values is not recommended if potassium nutrition is of concern.

Micro-Minerals - Copper(Cu), Iron (Fe), manganese (Mn) and zinc (Zn) are the trace minerals measured in the New Brunswick Lab using the same ICP method described for macro-minerals.

In many cases, rations are formulated assuming that no trace minerals are present in the natural feedstuffs, i.e. the animal. s entire trace mineral requirement is added to the diet and any naturally occurring trace mineral is considered as the safety margin. Trace mineral levels are useful in establishing typical farm or Provincial values and may warrant attention in problem solving situations. Because of their wide variation, numbers must be used cautiously.

ANALYSES OF POSSIBLE INTEREST BUT NOT AVAILABLE THROUGH NBDARD LAB

Almost any element, compound or organism can be analyzed for if the need arises. Many labs exist in North America that can be used when research or problem-solving efforts lead to the need for analyses numbers not provided in the NB Lab. Some of the analyses most likely of interest to livestock producers are listed below. An estimate of cost is included as an aid in deciding whether to proceed with a particular analysis. Some items have a large range in cost reflecting different lab methods, detection limits, lab specialty or analyses packaging.