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2006 Feed Composition

Nutrition research spanning more than a century has defined the nutrients required by animals. With such data, diets can be formulated to meet these requirements with the expectation that animals will not only remain healthy but productive and efficient.

An actual analysis of a feed to be used in a diet is much more accurate than the use of tabulated composition data. And, actual analysis should be obtained and used whenever possible. But, it's often difficult or impossible to utilize analysis in determining actual composition. Tabulated data, such as that on pages 59-66, are the next best source of information.

In using tabulated data, one can expect the organic constituents (e.g., crude protein, ether extract, crude fiber, acid detergent fiber and neutral detergent fiber) to vary as much as ±15%; the mineral constituents to vary as much as ±30%; and the energy values to vary up to ±10%. Thus, the values shown on the following pages can only serve as guides. That's why they're called “typical values.” They aren't averages of published information since judgment was used in arriving at some of the values in the hope these values will be realistic for use in formulating cattle and sheep diets.

New crop varieties usually result in nutrient composition changes. Genetically modified crops, for instance, will result in feeds with generally improved nutrient content and availability, and/or decreased anti-nutrient factors.

 

Chemical vs. biological attributes
Feeds can be chemically analyzed for many things that may or may not be related to an animal's response when fed the feed. Thus, in the accompanying table, certain chemical constituents are shown.

The response of animals when fed a feed can be termed the “biological response.” It's a function of its chemical composition and the ability of the animal to derive useful nutrient value from it.

The latter relates to the digestibility or availability of a nutrient in the feed for body absorption, and its ultimate efficiency of use depending on the animal's nutrient status and the productive or physiological function being performed by the animal. Thus, ground fence posts and shelled corn may have the same gross energy value but markedly different useful energy value (TDN or net energy) when consumed by the animal.

Therefore, “biological attributes” of a feed have much greater meaning in predicting animals' productive response but are more difficult to accurately determine because of the interaction between the feed's chemical composition with the animal's digestive and metabolic capabilities. Feeds' biological attributes are more laborious and costly to determine, and more variable than chemical constituents. They are generally more predictive, however, since they relate to the animal's response to the feed or diet.

 

Source of table information
Several sources of information were used in arriving at the typical values shown in the table. Where information wasn't available, but a reasonable estimate could be made from similar feeds or stage of maturity, this was done.

Where zeros appear, the amount is so small it can be considered insignificant in practical diet formulation. Blanks indicate the value is unknown.

 

Using the table information
Feed names:
The most obvious or commonly used feed names are used in the table. Feeds designated as “fresh” are feeds grazed or fed as fresh-cut materials.

 

Dry matter: Typical dry matter (DM) values are shown but moisture content of feeds can vary greatly. Thus, DM content can be the biggest reason for variation in feedstuff composition on an “as-fed basis.”

For this reason, chemical constituents and biological attributes of feeds shown in the table are on a DM basis. Since DM can vary greatly, and the feed's DM is one factor regulating total feed intake, diet formulation on a DM basis is more sound than using “as-fed basis.” If one wants to convert a value to an as-fed basis, multiply the decimal equivalent of the DM content times the compositional value shown in the table.

 

Energy: The table uses four measures of energy value in feeds. TDN (total digestible nutrients) is used because more such values for feeds exist, and it's the standard for expressing feeds' energy value for cattle and sheep.

There are several technical problems with TDN, however. For one, the digestibility of crude fiber (CF) may be higher than for nitrogen-free extract (NFE) in certain feeds. TDN also overestimates roughage value compared to concentrates in producing animals.

Some argue that since energy isn't measured in pounds or percent, TDN isn't a valid energy measure. But, this is more a scientific argument than a criticism of TDN's predictive value.

Digestible energy (DE) values aren't included in the table. There's a constant relationship between TDN and DE in cattle and sheep: calculate DE (Mcal/cwt.) by multiplying the %TDN content by 2. TDN and DE's abilities to predict animal performance are equal.

Interest in using net energy (NE) in feed evaluation was renewed with development of the California Net Energy System. This is due to the improved predictability of results depending on whether feed energy is being used for maintenance (NEm), growth (NEg) or lactation (NEl).

The major problem in using these NE values for growing cattle and sheep is predicting feed intake, and thus the proportion of feed that will be used for maintenance and growth. Some only use NEg values, but this suffers the equal but opposite criticism mentioned for TDN — NEg will overestimate the feeding value of concentrates relative to roughages.

The average of the two NE values can be used, but this would be true only for cattle and sheep eating twice their maintenance requirement. The most accurate way to use these NE values to formulate diets is to use the NEm value, plus a multiplier, times the NEg value, all divided by 1, plus the multiplier. The multiplier is the level of feed intake above maintenance relative to maintenance.

For example, if 700-lb. cattle are expected to eat 18 lbs. DM, 8 lbs. of which will be required for maintenance, the diet's NE value would be: NE = [NEm + (10/8)(NEg)]/[1 + (10/8)]

Such a calculation can be easily introduced into computer programs designed to formulate diets and predict performance.

In deciding on the energy system to use, there's no question of NE's theoretical superiority over TDN in predicting animal performance. But, the superiority is lost if only NEg is used in formulating diets. If NE is used, some combination of NEm and NEg is required. NEl values are also shown, but few of them have actually been determined. However, NEl values are similar to NEm values except for very high- and low-energy feeds.

 

Protein: Crude protein (CP) values are shown for each feed, which are Kjeldahl nitrogen times 100/16 or 6.25, since proteins contain 16% nitrogen on average. CP doesn't give any information on the actual protein and non-protein nitrogen (NPN) content of a feed.

Digestible protein (DP) has been included in many composition tables. But, because of the contribution of microbial and body protein to the protein in feces, DP is more misleading than CP. One can estimate DP from CP content of the diet fed to cattle or sheep by the following equation:

%DP = 0.9(%CP) -3, where %DP and %CP are the diet values on a DM basis.

Undegradable intake protein (UIP, rumen bypass or escape protein) values are shown. This value represents the percent of CP passing through the rumen without degradation by rumen microorganisms.

Degradable intake protein (DIP) is the percent of CP degraded in the rumen and is equal to 100 minus UIP. Like other biological attributes, these values aren't constant. UIP values on many feeds have not been determined and reasonable estimates are difficult to make.

How should these values be used to improve the predictability of animal response when fed various feeds? Generally, DIP can supply CP up to 7% of the diet. If the diet's required CP exceeds 7% of DM, all CP above this amount should be UIP.

In other words, if the final diet is to contain 13% CP, six of the 13 percentage units, or 46% of the CP, should be in the UIP form. Once the relationships between UIP and DIP have been better quantified, CP requirements can be lowered, especially at higher CP levels. In diets high in rumen fermentable carbohydrate, DIP requirements may determine total CP needed in the diet.

 

CF, ADF and NDF
After more than 125 years, crude fiber (CF) is declining in use as a measure of poorly digestible carbohydrates in feeds. CF's major problem is that variable amounts of lignin, which isn't digestible, are removed in the CF procedure.

In the old scheme, the remaining carbohydrates (nitrogen-free extract, or NFE) were thought to be more digestible than CF despite many feeds having a higher CF digestibility than NFE. One reason CF remained in the analytical scheme was its apparent requirement for TDN calculation.

Improved analytical procedures for fiber have been developed, namely acid detergent fiber (ADF) and neutral detergent fiber (NDF). ADF is related to digestibility, while NDF is also somewhat related to voluntary intake and the availability of net energy. Both these measures relate more directly to predicted animal performance and thus are more valuable than CF. Lignification of NDF, however, alters the availability of surface area to fiber-digesting rumen microorganisms. Lignin, therefore, may be added to future tables.

Recently, effective NDF (eNDF) has been used to better describe the dietary fiber function in high-concentrate, feedlot-type diets. While eNDF is defined as the percent of NDF retained on a screen similar in size to particles that will pass from the rumen, this value is further modified based on feed density and degree of hydration.

Rumen pH is correlated with dietary eNDF when diets contain less than 26% eNDF. Thus, when formulating high-concentrate diets, including eNDF helps prevent acidosis in the rumen. In feedlot diets, the recommended eNDF levels range from 5-20% depending on bunk management, inclusion of ionophores, NDF digestion and/or microbial protein synthesis in the rumen. Therefore, estimated eNDF values are shown for many feeds. But, these values must be modified, depending on degree of feed processing (e.g., chopping, grinding, pelleting) and hydration (fresh forage, silages, high-moisture grains), if these feed forms aren't specified in the table.

Ether extract: Ether extract (EE) shows the crude fat content of the feed.

Minerals: Values are shown for only certain minerals. Calcium (Ca) and phosphorus (P) are important to consider in most feeding situations. Potassium (K) is more important as the concentrate level increases and when NPN is substituted for intact protein in the diet.

Sulfur (S) also becomes more important as the NPN level increases in the diet; high S levels in diets, compounded by high S levels in drinking water, can be detrimental, however. Zinc (Zn) is shown because it's less variable and more generally near a deficient level in cattle and sheep diets. Chlorine (Cl) is of increasing interest for its role in dietary acid-base relationships.

Iodine and selenium are required nutrients often deficient in many diets, yet their level in feed is related more to growing conditions than the feed itself. Trace-mineralized salt and trace mineral premixes are generally used to supplement trace minerals; their use is encouraged where deficiencies exist.

Vitamins: Vitamins are not included in the table. The only vitamin of general practical importance in cattle and sheep feeding is the vitamin A value (vitamin A and carotene) in feeds. It depends largely on maturity and conditions at harvest, and the length and conditions of storage. Thus, it's unwise to rely entirely on harvested feeds as a source of vitamin A value.

Where roughages are fed that contain good green color, or are being fed as immature fresh forages (e.g., pasture), there will probably be sufficient vitamin A value to meet animal requirements. Other needed vitamins should be supplied as supplements.

Future table revisions
A feed composition table is of value only if it's relatively complete, contains feeds commonly fed, and data constantly are updated. I welcome suggestions and compositional data to keep this table useful to the cattle and sheep feeding industry.

When sending compositional data, adequately describe the feed, indicate the DM or moisture content and if analytical values are on an as-fed or DM basis. If more than one sample was analyzed, the number analyzed should be indicated.

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