FGV-00243D

Obtaining a feed analysis is an important first step in formulating balanced, economical livestock rations; but it is just that-a first step. The next step is to study the analysis and determine how the feed can best be used for your animals. To do this, you must be able to interpret the results reported on the analysis form.

Dry Matter

The first figures shown in Table I indicate the amount of dry matter in the feed samples. You can determine the moisture content by subtracting the dry matter figure in the "AS FED" column from the dry matter figure in the "MOISTURE FREE" column. Knowledge of the dry matter content of a feed is important, since it greatly influences the amount of feed that must be fed to meet an animal's nutrient requirements. This is especially important when dealing with high moisture feeds such as silage, which may contain as much as 80% moisture, or, high moisture barley, which may contain 25% moisture or more. A mature dairy cow that has a dry matter requirement of 25 pounds per day would have to be fed 70 pounds of silage that contains 65% water, however, if she were fed 10% moisture hay, only 28 pounds would be needed to supply her dry matter needs. Likewise, feeds that contain high amounts of water contain lower amounts of other nutrients per pound than do dry feeds. Normal levels for dry matter in the "AS FED" column would be 88% to 92% for grains and hays, and 30% to 40% for silages.

Crude Protein

Crude protein is reported as all the protein in a feed sample. Nutrients are not totally available to the animal due to the indigestibility of some materials in the feed. Compounds such as lignin cause cell walls to be rather indigestible, and since most of the protein is within the cell, its availability is limited. You might think that this digestibility problem would make the crude protein figure a poor indicator of the actual protein value of the feed. In reality, the vast majority of feeds are very predictable as to protein digestibility. Protein digestibility in grains is about 80%, and in forages it is about 50%. While these are fairly rough approximations, they are adequate for most rations. If you apply these digestibility estimates to the crude protein values in Table 1, the estimated digestible protein for the brome hay is 5.3% on a moisture free basis.

Book values for brome hay having the same crude protein show digestible protein to be 5.4%. The values in the book were determined by scientific research trials and are not simple approximations. In this example, using the 50% digestibility rule of thumb brings the hay sample very close to values determined by years of direct measurement. If you do the same exercise for barley, you find the results to be nearly as close as for the hay. If anything, the 80% figure for grains tends to overestimate the digestibility of barley somewhat for swine and poultry. As the test weight of mature barley decreases, so does its digestibility, especially for the animals previously mentioned. This is due to an increased proportion of fiber in the lightweight grain. Crude protein in barley varies considerably with test weight, plant maturity, fertilization practices and, to a lesser extent, variety. Alaskan barley and brome hay average about 11% crude protein on a dry matter basis. Alaskan hulless barley averages 12.5% crude protein. Compared to feeds such as soybean meal or fishmeal, neither barley nor brome hay is considered to be a good source of protein and should be fed mainly for their energy content.

Phosphorus

Phosphorus is considered to be a major mineral and is usually higher in grains than in forages. Grains usually run between .25% and .40% phosphorus on a dry matter basis. Grass hays have phosphorus contents in the range of .15% to .22% on a dry matter basis.

Calcium

Calcium is the third nutrient listed in the analysis report. It, too, is considered to be a major mineral, but in contrast to phosphorus, calcium is usually higher in forages than in grains. Dry hays usually contain between .30% and .40% calcium, while grains contain between .03% and .10% on a dry matter basis.

Potassium

A third major mineral listed on the report is potassium. Like calcium it is normally found in higher concentrations in dry forages than in grain. On a dry matter basis, levels ranging from 1.50% to 4.00% are normal in various hays, while grains contain between 0.30% and 0.80% on a dry basis. Alaskan feeds fall within these values and seldom do we see dietary deficiencies of this nutrient.

 Acid Detergent Fiber

As you might suspect, acid detergent fiber (ADF) is a measure of the fiber content of the feed. As fiber content increases, digestibility of the feed decreases. This is true for all animals, and especially for species with simple stomachs, such as swine and poultry. Ruminants such as sheep, cattle and goats are better able to digest fiber by virtue of microbial fermentation in the rumen. While it is true that the make-up of the fiber content of feeds varies and that some are much more indigestible than others, it is sufficient to simply judge the digestibility of the vast majority of feeds on their "ADF" value alone. On a dry matter basis, average ADF values for covered barley, hulless barley and grass hay in Alaska are 7.8%,1.9% and 38%, respectively.

In Vitro Dry Matter Disappearance

The next values on the analysis report are for in vitro dry matter disappearance (IVDMD). It is determined by measuring the dry matter disappearance of a feed sample after it has been subjected to digestion by microorganisms taken from an animal's rumen, and by pepsin, a proteolytic enzyme, in sequence much as it occurs in an animal. IVDMD is an estimate of feed digestibility and is used to calculate metabolizable energy. Think of it as a measure of "energy digestibility." As IVDMD increases, energy in the feed becomes more available. On a dry matter basis, covered barley, hulless barley and grass hays in Alaska have average IVDMD values of 76.1%, 89.2% and 56%, respectively.

Total Digestible Nutrients

In the early 1900s a team of researchers in Vermont and Wisconsin coined the phrase "total digestible nutrients" (TDN). They defined it as the sum of the energy values for the digestible protein, fats and carbohydrates found in a feed sample. While the resulting number is probably adequate for formulating diets for animals raised on most farms, it somewhat overstates the true energy value of the feeds being tested. This is because it fails to take into consideration energy lost through urine and gases as well as other factors. While you can usually be accurate enough using TDN values to formulate most livestock rations, the figures shown on the
analysis form for IVDMD and metabolizable energy are more realistic estimates of the energy found in a feed. On a dry matter basis, TDN values for forages fall in the range of 45% to 55%, while for grains they run between 75% and 85%.

Metabolizable Energy

Metabolizable energy (ME) is the amount of energy in the feed after you deduct the amount that leaves the animal in the urine, feces and gasses. This is a very critical value for grains and forages, since they contribute the major portion of the energy in a ration. In Alaska ME is used as a measure of energy because it is quickly and inexpensively estimated by laboratory analysis and is adequate for general ration formulation. On a dry matter basis, covered barley, hulless barley and grass hays in Alaska have average ME values of 1.20, 1.41 and .90 Mcal/lb, respectively.

Net Energy-Lactation

Net energy for lactation (NEL) is an expression of the feed's energy value relative to the production of milk. This needs to be considered when formulating diets for lactating dairy cows or dairy goats. Simply stated, the energy required to produce one pound of milk is less than that needed to produce one pound of fat, but more than needed to supply the equivalent energy needs for body maintenance. Diets for lactating dairy animals are rather complex and you should consult a professional nutritionist for help. When balancing diets for these animals, use either IVDMD, TDN or ME to calculate the amount of feed needed to meet the maintenance requirement of the animal. Then use the NEL value to calculate the extra amount needed for the production of milk.

Interpretation of a feed analysis lets us evaluate a feed for the contribution it can make to livestock rations. You should include feeds in a ration according to their most prevalent nutrient. For example, feeds high in protein, such as crabmeal, should not be put into the ration to supply energy. Carbohydrate feeds, such as barley, provide higher levels of energy at less cost. Likewise, barley should not be used as a protein supplement, since its cost per unit of protein is much higher than other feeds like fishmeal or soybean meal.

A simple way to determine which feeds to use in a ration is to compare the cost of the nutrients on a per unit basis. For example, if barley that contains 10% crude protein costs $130/ton, the cost of a ton of crude protein from that barley would be $1,300. On the other hand, if fishmeal that contains 60% crude protein costs $350/ton, the cost of a ton of crude protein from that fishmeal would be $583. In this example, it would be considerably cheaper to buy fishmeal as a protein source. Follow this same logic when choosing between feeds with similar nutrient contents like fishmeal and soybean meal. To determine the per pound cost of a nutrient for any given feed, use the following formula.

cost of feed per ton nutrient content of the feed expressed as a decimal	= cost per ton of nutrient
BARLEY EXAMPLE: $130.00 ÷ .10 (% crude protein) = $1,300.00/ton of crude protein. To convert the answer to a cost per pound, simply divide by 2,000. To convert it to a hundred weight basis, divide by 20.

Once a feed analysis is done and cost figures are applied to various nutrients, you can begin to formulate and balance a ration. Ration balancing is not difficult, but it does require some knowledge of nutrient relationships, limitations of various feeds, nutrient requirements of various classes of animals and the like. Producers are encouraged to take advantage of the free computer ration balancing service offered by the Cooperative Extension Service at the University of Alaska; contact your local extension office.

The feed analysis service provided by the University of Alaska's Palmer Laboratory is $20.00 per sample and the results can be obtained within a few weeks. There are many other equally good laboratories outside of Alaska where feed analyses may be done. It would be rare if all these labs used the same format and terminology to report the results of analyses. If you have an analysis report that you cannot interpret, ask your local agricultural extension agent for help.

Reference

Husby, F.M. and Krieg, K.L., 1987. Alaska's Feeds for Alaska's Livestock. Circular 63, Agricultural and Forestry Experiment Station, School of Agriculture and Land Resources Management, University of Alaska Fairbanks.

Tom Jahns
Land Resources District Agent
phone (907) 262-5824
email: fftrj@uaf.edu

111/5-86/KK/200 Reprinted February 1999

The University of Alaska Fairbanks Cooperative Extension Service programs are available to all, without regard to race, color, age, sex, creed, national origin, or disability and in accordance with all applicable federal laws. Provided in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Anthony T. Nakazawa, Interim Director, Cooperative Extension Service, University of Alaska Fairbanks.

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