Chapter 4 Sampling and analysis.
The key to balancing rations for livestock is in knowing the nutrient content of what you have to work with. Finding out the nutrient content involves using proper sampling technique and laboratory analysis. Applying this information requires an ability to interpret the analysis results reported by the laboratory.
VARIATION IN FEEDSTUFF NUTRIENT CONTENT
The nutrients required by livestock are supplied in balanced rations by feed ingredients or feedstuffs. Feedstuffs vary in the nutrients they contain and in the availability of these nutrients to livestock. This variation is quite consistent with grains, protein supplements, and mineral and vitamin supplements. In fact, for these feedstuffs, it is usually acceptable to use analysis values in reference sources. However, for forages, the variation is not consistent. The analysis of this year's alfalfa crop may be dramatically different than that for last year's crop so that average values will not be useful in developing a balanced ration. Forages, such as alfalfa, form the foundation of diets for ruminants (beef, dairy, sheep, and goats), horses, and rabbits. However, for growing, working, and lactating animals, forages will not provide sufficient nutrients to meet requirements. Supplemental feedstuffs containing more concentrated sources of nutrients must be a part of these animals' diets. It is important to recognize that supplementation of any nutrient beyond the requirements will not benefit the animal being fed, and excessive supplementation may create toxicity problems. Therefore, supplements should be used to address specific deficiencies. Again, to know what deficiencies exist in animal diets, each lot of forage must be properly sampled and sent to a laboratory for analysis of nutrient content.
A knowledge of the nutrient content of a feedstuff helps determine the potential usefulness of that feedstuff in a ration. Analytical methods have been developed that make it possible to measure feedstuff nutrient content for a large number of nutrients. These values are of no practical use, however, if the sample received by the laboratory is not representative of the feedstuff as it is fed to livestock. Collecting a representative feedstuff sample is, therefore, the first step of the analytical process. Following recommended sampling procedures will help ensure that the laboratory results truly reflect the nutritive value of the feedstuff.
The following forage sampling procedures are adapted from the Dairy One Forage Laboratory mailer insert (2001). Images and supplemental information related to feed sampling are found in the file titled Images.ppt on the text's accompanying On-Line Companion. To view this file please go to http://www. agriculture.delmar.com and click on Resources. Click on On-Line Resources and select from the titles listed.
Hays of different types, cuttings, or lots should be sampled separately. Using a hay probe, bore 12 to 20 bales selected at random. Combine all core samples, and from this, submit a subsample for analysis.
Grab handfuls of silage from 12 to 20 locations in the unloaded silo pile, across the silo face, in the feed bunk, or from in front of 12 to 20 animals. All subsamples should be combined and thoroughly mixed in a clean plastic bucket to form a composite sample. Submit 1 lb. of the composite for analysis.
Randomly select 12 to 20 sites where the animals have been grazing and clip the forage at grazing height. All subsamples should be combined and thoroughly mixed in a clean plastic bucket to form a composite sample. Take a 1-lb. composite sample, pack tightly in a plastic bag, and freeze for 12 hours prior to submitting for analysis. Freezing will help prevent marked chemical changes due to respiration or fermentation.
Grains and Ingredients
Bin storage: Randomly collect 12 to 20 samples as the grain is discharged and combine in a clean plastic bucket.
Flat storage: Grab 12 to 20 samples from various sites and combine in a clean plastic bucket. Thoroughly blend and submit a 1-lb. sample for analysis.
Note: wherever possible, a grain probe should be used to take the sample.
Feed microscopy is a complement to routine chemical quality-control analyses. It involves an evaluation by a trained microscopist to provide a rapid evaluation of ingredient or finished feed quality. Feed microscopy produces a subjective opinion that can be a useful component of a feed mill's quality-assurance program. Feed microscopy can be used to identify weeds, insects, molds, and mold spores, and otherwise contaminated, adulterated, or damaged feedstuffs arriving at the mill's receiving area.
Feed microscopy may be used to evaluate feed particle size. Particle size information may, in turn, be used to improve manufacturing processes, or adjustments may be made to improve the health and performance of livestock consuming the feed. Feed microscopy can also be used to evaluate mixing efficiency and ingredient-segregation problems.
ANALYSIS PROCEDURES AND VALUES
One of the oldest laboratory methods for predicting the value of a feedstuff for animals is a system of chemical analysis termed proximate analysis. By appropriate analytical procedures, the components of a feedstuff can be divided into six categories: crude protein, crude fiber, nitrogen-free extract, crude fat (ether extract), ash, and moisture. These classifications can give some information about the usefulness of a feedstuff.
Table 4-1 shows the feedstuff carbohydrate components as partitioned in proximate analysis. Notice that the hemicellulose and lignin fractions are split between crude fiber and nitrogen-free extract. Because hemicellulose is digestible and lignin is not, feedstuffs that potentially have significant amounts of hemicellulose and/or lignin are not well described by crude fiber and nitrogenfree extract. Such feedstuffs include forages such as pastures, hay crops, corn silage and sorhgum silage, as well as some common byproducts including distillers' grains, brewers' grains, and beet pulp.
The average protein molecule contains about 16 percent nitrogen. This value is used to estimate the protein content of feed samples. The Kjeldahl procedure of proximate analysis is used to measure the nitrogen content of a sample. The nitrogen value is multiplied by 6.25 to obtain the approximate protein content (Figure 4-1). Because protein is not the only feed component that contains nitrogen, this calculated value is called crude protein.
In livestock nutrition, crude protein is not an adequate description of feed protein value. In monogastric nutrition, the amino-acid content of protein must be known because ration balancing involves meeting amino-acid requirements using feed protein sources. In ruminant nutrition, feed protein needs to be described according to its susceptibility to microbial degradation in the rumen. Though crude protein content must be stated on the feed tags accompanying the sale of commercial feeds, it is also a legal requirement that feed tags specify the amount of this crude protein coming from nitrogen-containing compounds other than true protein. On the feed tag, this is given as percent equivalent crude protein from nonprotein nitrogen, as fed basis (Figure 4-2). In the companion application to this text, the equivalent crude protein from nonprotein nitrogen is calculated when blending feedstuffs for ruminants.
Figure 4-1 Calculating a feedstuff's crude protein content The average protein molecule is 16% nitrogen. Percent means parts per 100 parts, so this can be restated as 16 parts nitrogen/100 parts protein. The reciprocal is also true: 100 parts protein/16 parts nitrogen. If a feed sample tests at 3% nitrogen, its approximate protein content can be calculated as follows: 100 parts protein/16 parts nitrogen x 3 parts nitrogen/100 parts feed = 0.1875 parts protein/1 part feed In percentage form, this is 18.75%. The calculation can be simplified by multiplying the result of 100/16 by the feed's percentage of nitrogen: 100/16 x 6.25 In the previous example, 3% x 6.25 = 18.75% Figure 4-2 Calculating equivalent crude protein from nonprotein nitrogen If a 2000-lb. mix contained 30 lbs. of urea, which contains 45% nitrogen (N), the calculation of equivalent crude protein (CP) from nonprotein nitrogen, as fed basis, would be: 30 lb. urea/2000 lb. mix x 45 lb. N/100 lb. urea x 100 lb. CP/16 lb. N x 100 = 4.22%
In ruminant nutrition, feed protein is described as degradable, undegradable/ digestible, or undegradable/indigestible. Degradable protein is degraded in the rumen and used by the microbes. Undegradable/digestible protein is resistant to microbial activities, and arrives at the small intestine intact where it is digested and absorbed. Undegradable/indigestible protein bypasses the rumen and is indigestible in the small intestine, and emerges in the feces. The characterization of these protein fractions is described in Chapter 7.
The application of heat to a feedstuff can change the digestibility characteristics of its protein. During the fermentation process, for example, silages sometimes heat excessively, potentially changing the protein. This heat leads to a reaction between the carbohydrate and protein in the feed. Acid detergent fiber insoluble protein (ADFIP) on the forage analysis identifies unavailable protein, including that lost to heat damage.
Neutral detergent fiber insoluble protein (NDFIP) is used in protein and energy calculations in ruminant nutrition. NDFIP is an estimation of the portion of the crude protein that is true protein but slowly degraded or undegradable in the rumen. ADFIP, which is not only undegradable in the rumen but also indigestible in the small intestine, is a subset of NDFIP. NDFIP minus ADFIP identifies slowly degraded or undegradable, digestible true protein.
NDFIP is also used to calculate the digestible energy (DE) content of some feedstuffs through its use in the calculation of digestible neutral detergent fiber (NDF) and digestible nonfiber carbohydrate (NFC).
It should be noted that ADFIP and NDFIP were designed to evaluate forages and are not considered useful indicators of heat exposure with animal byproducts and nonforage plant protein sources (Satter, Dhiman, & Hsu, 1994).
For forages, the Van Soest system is used to partition forage carbohydrate components in a more useful way than is possible with the proximate analysis method. Table 4-2 shows the components of the Van Soest system.
Structural carbohydrates, measured as NDF, constitute the cell wall of a plant. The cell walls of plants can be compared to reinforced concrete in which the reinforcing steel bars are represented by the cellulose fibrils, and the concrete is represented by the matrix material that includes hemicellulose and an indigestible polymer called lignin. NDF includes the fiber fractions cellulose, hemicellulose, lignin, and NDFIP. Acid detergent fiber (ADF) is the NDF less the most digestible fiber component, hemicellulose. To the extent that a feedstuff's ADF content is high, it will be of low digestibility. Figures 4-3a and 4-3b show the procedures used to measure NDF and ADF content of feedstuffs.
[FIGURE 4-3a OMITTED]
[FIGURE 4-3b OMITTED]
Because NDF is a mixture of substances that vary in digestibility, it is important to identify NDF digestibility when formulating rations, especially those for ruminants. In this text's dairy application, the NDF digestibility (NDFdig) is calculated as follows (NRC, 2001):
NDFdig - (0.75 x [[NDF% - NDFIP%] - Lignin%] x (1 - [[Lignin % / (NDF% - NDFIP%)].sup.0.667]]) / NDF%
Nonstructural carbohydrate (NSC) and NFC refer to the cell contents. NSC is a measured value and includes sugars and starch. NFC is a calculated value and includes starch, sugar, organic acids, and pectin. NFC percent can be calculated as follows:
100 - [% crude protein + (% NDF - % NDFIP) + % crude fat + % ash]
Table 4-3 summarizes how the various feed carbohydrates are partitioned on a feed analysis. Table 4-4 gives selected feedstuffs and the analysis of their carbohydrate content.
In ruminant nutrition, a system paralleling that of the protein degradability systems is being used for carbohydrate. The carbohydrate in a given feedstuff is described, based on its degradability and digestibility characteristics. The various analysis values for these carbohydrate fractions are described in Chapter 6.
Lipids are high-energy components of feedstuffs that contain a higher proportion of hydrogen to oxygen than do carbohydrates. The increased number of hydrogen bonds means more energy is stored in lipids than in carbohydrates. A pound of lipid will contain at least 2.25 times as much energy as a pound of carbohydrate. Lipids that exist as a liquid at room temperature are often referred to as oils and those that are solid at room temperature are referred to as fats. In feed analysis, lipid content is determined using a solvent extraction method. The solvent used is typically diethyl ether, so feedstuff lipid content is sometimes referred to as ether extract. In addition to lipids, compounds such as waxes and resins are also soluble in ether, so to the extent that feedstuffs contain these compounds, ether extract is not an accurate estimation of lipid content. For some applications, the ether extract percentage value is reduced by one to better approximate the true lipid content.
Ash is an approximation of the total mineral (inorganic) portion of the feed sample. It is obtained by oxidizing the sample in a furnace at 500[degrees] to 600[degrees]C. Ash is useful in determining the feedstuff content of organic components that cannot be measured directly, such as NFC. Recall that NFC is a calculated value and that the formula includes the feedstuff's ash content. Ash content of diets is of special concern for cats and fish. In cat nutrition, high-ash diets have been suggested as possible contributors to feline lower urinary tract disease. Fish meal is a primary component of fish diets, and a high ash content in this feedstuff may indicate that the product contains an unacceptably high bone content.
Total Digestible Nutrients
Total digestible nutrients (TDN) is a measurement of the digestible organic constituents of the feedstuff (Figure 4-4). Because any of the organic constituents could be used by the animal as a source of energy, TDN has historically been used to describe an animal's energy requirement and to assess a feedstuff's energy value for a given species of livestock. TDN is no longer used for these purposes, but it still may be used as an intermediate calculation to arrive at more useful values.
Figure 4-4 Total digestible nutrients Total digestible nutrients = Digestible crude protein + Digestible crude fiber + Digestible nitrogen-free extract + Digestible ether extract or crude fat x 2.25
In the TDN formula, the digestible crude fat is multiplied by 2.25 because TDN is an assessment of a feedstuff's energy value, and a pound of fat provides 2.25 times as much energy as a pound of any of the other organic constituents of TDN.
The values used in the TDN formula are determined by multiplying a feedstuff's proximate analysis values for crude protein, crude fiber, nitrogen-free extract, and crude fat by their respective digestion coefficients. The digestion coefficients for a particular feedstuff are found by performing a digestion trial.
In a digestion trial, the percentage of each nutrient in the feedstuff is determined through proximate analysis. A weighed amount of the feedstuff is then fed to the animal during the test period. The feces are collected, weighed, and analyzed using proximate analysis. The amount of each nutrient digested is assumed to be the difference between the amount consumed and the amount excreted. The proportion of each nutrient digested is the digestion coefficient for that nutrient for that feedstuff.
The dairy NRC (2001) does not use digestion trial data to determine feedstuff TDN. Instead, TDN is calculated from feedstuff composition values obtained through in vitro techniques. The formulas used vary with the feedstuff type and are shown in the companion CD-ROM for dairy at F9.
Other Feed Analysis Issues and Values
As discussed previously, TDN was formerly used to assess a feedstuff's energy value and to describe an animal's energy requirement. For this purpose, TDN has been replaced by a system that describes the fractions of a feedstuff's energy content available to the animal and those fractions that are not available to the animal. This system and its application to animal nutrition are described in Chapter 5.
Near Infrared Reflectance Spectroscopy
Near Infrared Reflectance Spectroscopy (NIR) is a sophisticated analytical method that many feedstuff analysis laboratories have available. For many feedstuff types, NIR produces rapid results with a minimum amount of labor and will be less expensive than the traditional wet chemistry analysis.
NIR involves measuring reflected light in the near infrared region from a ground sample. The equipment uses equations that have been established for the specific type of feedstuff to be tested. An accurate description of the feedstuff sample is, therefore, critical. Because minerals do not absorb light in the near infrared region, errors in a feedstuff's mineral content will be greater in an NIR analysis than those for organic feedstuff components.
Sampling Total Mixed Rations
Total mixed rations (TMR) are rations that are mixed on the farm and include all ingredients fed. Laboratories are sometimes asked to analyze TMR samples for nutrient content to meet one or more of the following objectives:
1. To determine if the mix is meeting nutrient specifications.
2. To determine if the mixer is working properly.
3. To determine if the mixer is being used properly.
Figure 4-5 Calculating relative feed value All values are given on a dry matter basis. % DDM = 88.9 x (ADF % x 0.779) % DMI = 120/% NDF RFV = (% DDM x % DMI)/1.29
Many variables influence the results of TMR analysis, and money is better spent meeting the above goals through other means. To determine if the mix is meeting nutrient specifications, the feeder should reanalyze and confirm the nutrient composition of the individual ingredients and compare ration nutrient levels with predicted requirements. To determine if the mixer is working properly, the best testing method is as follows:
1. Add a tracer product to the mixer.
2. Take several samples of the mix.
3. Count the amount of tracer present in all samples.
4. Apply statistics to evaluate the effectiveness of the mixer.
To determine if the mixer is being used properly, employee training and supervision is the best solution.
Relative Feed Value
Another value that is often reported on a forage analysis is the relative feed value (RFV). This is calculated from the percentage digestible dry matter (DDM) and the dry matter intake (DMI) as a percentage of body weight for mature dairy cows ( Figure 4-5). RFV is designed as a tool to assist in marketing forage products; it is not used in ration formulation.
Relative Forage Quality
Relative forage quality (RFQ) is intended to replace RFV. Unlike RFV, RFQ accounts for differences in NDF digestibility. The more digestible the NDF in a forage, the more the forage behaves like a grain. This means that more of this highly digestible forage can replace grain without sacrificing production, but it also means that the forage is less helpful in reducing the risk of acidosis (Chapter 20).
RFQ values will be similar to RFV values if NDF digestibility is "average." However, where NDF digestibility varies considerably, as is the case with grasses, RFQ will give a better estimate of the feedstuff's value.
Expressing Nutrient Concentration
Laboratories that perform feedstuff analyses report nutrient concentrations on two bases: as fed and dry matter. The "as fed" or "as sampled" basis is used by feed manufacturers because it is also the basis on which the feed is bought and sold. The as fed or as sampled basis is also the basis on which feed nutrient content must be reported in accordance with laws pertaining to the feed industry. However, nutritionists prefer to use nutrient analyses on a dry matter basis because a feedstuff's water content is largely irrelevant once the feedstuff is eaten. In discussing silage quality, nutrient content is expressed on the dry matter basis to ensure that accurate comparisons of nutrient content are made in feedstuffs of varying water content.
Nutrient concentration expressed on a dry matter basis will be a larger value than nutrient concentration expressed on an as fed or as sampled basis (Figure 4-6 and Figure 4-7a). The companion application to this text uses dry matter as the standard basis in expressing nutrient concentration.
Figure 4-6 Dry matter and as fed basis conversions To convert from dry matter to as fed basis: Nutrient content, as fed basis = Nutrient content, dry matter basis x decimal of % dry matter To convert from as fed to dry matter basis: Nutrient content, dry matter basis = Nutrient content, as fed basis/ decimal of % dry matter
[FIGURE 4-7a OMITTED]
[FIGURE 4-7b OMITTED]
Percentage is one way of expressing nutrient concentration in feedstuffs. Percentage represents parts of nutrient per 100 parts of feedstuff. The "part" may be any measured amount: pounds, grams, milligrams, kilograms, and so on. Examples of feed nutrients for which concentration is usually expressed as a percentage include dry matter, protein, amino acids, carbohydrate components, and macrominerals.
Energy, micromineral, and vitamin concentration in feedstuffs are not expressed as percentages. Energy concentration is expressed in kilocalories (Kcal) or megacalories (Mcal) of digestible energy (DE), metabolizable energy (ME), or net energy (NE) per pound of feedstuff. These energy values are described in Chapter 5. Micromineral concentration is expressed in milligrams per kilogram, which is the same as parts per million (ppm). Vitamin concentration in feedstuffs is expressed in milligrams or International Units of vitamin per kilogram or per pound of feedstuff.
Expressing Feedstuff Amounts
This text uses the pound as the standard unit in expressing feedstuff amounts. The kilogram (kg) is the standard in the scientific literature. There are 2.2046 pounds in 1 kg. Be aware that the 2.2046 value is used differently when converting from pounds to kilograms than when converting from kcal/lb. to kcal/kg. See Figure 4-7a, 4-7b, and 4-7c for conversion explanations.
[FIGURE 4-7c OMITTED]
FEED LAWS AND LABELING
The Official Publication of the Association of American Feed Control Officials (2003) contains a model bill for state legislators to consider when making laws pertaining to the labeling requirements of feeds sold in their state. A primary purpose of the model bill is to promote consistency among the state laws pertaining to feed tags and thereby facilitate feed sales across state lines. The feed tag, then, is a mercantile instrument. As such, it will seldom supply sufficient information for meaningful ration formulation.
Chapter 4 emphasizes the importance of laboratory analysis for forages. Proper sampling involves taking 12 to 20 samples, combining these, mixing them, and then obtaining a subsample for analysis. Feed microscopy is described as a subjective means of assessing feed quality. Analysis procedures available from feed analysis laboratories are described. Energy is perhaps the most important nutrient, but because livestock can acquire energy from any organic component of feed, assessing feed energy value is problematic. The NE system involves assessing feed energy content by systematically removing sources of wasted energy until the NE--what remains--represents the energy actually available to the animal. The feed labels as required by law are described as being of limited value in providing useful information toward the development of livestock rations.
1. Describe the proper technique for acquiring a sample of a supply of feedstuff to submit for analysis.
2. What are the components of neutral detergent fiber?
3. What are the components of nonfiber carbohydrate?
4. If a given weight is expressed in units of both pounds and kilograms, which unit has the lowest numerical value?
5. If a given nutrient concentration is expressed both on an as fed and dry matter basis, which concentration value is the highest numerical value?
6. Compare the utility of the Van Soest and proximate analysis methods for expressing the carbohydrate content of forages.
7. The Kjeldahl procedure measures the nitrogen content of a feed sample. The nitrogen content is then multiplied by 6.25 to arrive at the crude protein content. What assumption is made when using the 6.25 value?
8. What fraction of the feedstuff is included in the ash fraction?
9. In addition to the concentration of crude protein, what additional protein information is used in ruminant nutrition? What additional protein information is used in monogastric nutrition?
10. How is NIR used to analyze feedstuff nutrient content? Discuss the strengths and weaknesses of NIR as a method of feedstuff analysis.
Association of American Feed Control Officials. (2003). Official Publication. West Lafayette, IN.
Dairy One Forage Laboratory. (2001). Mailer insert. Dairy One Forage Laboratory. Ithaca, NY.
Miller, T. K., & Hoover, W. H. (1998). Nutrient analyses of feedstuffs including carbohydrates. Animal Sci. Report #1, West Virginia University.
National Research Council. (2001). Nutrient requirements of dairy cattle (7th revised edition.). Washington, DC: National Academy Press.
Northeast DHIA, Dairy Herd Improvement Association. (1995). Forage analysis statistics. Ithaca, NY.
Satter, L. D., Dhiman, T. R., & Hsu, J. T. (1994, October 18-20). Use of heat processed soybeans in dairy rations. In Proceedings Cornell Nutrition Conference for Feed Manufacturers (pp. 19-28). Rochester, NY.
Table 4-1 Feed carbohydrates as identified in the proximate analysis procedure Relative Nitrogen-Free Component Digestibility (1) Crude Fiber Extract Sugar 1 [check] Starch 1 [check] Hemicellulose 2 [check] [check] Cellulose 3 [check] Lignin 4 [check] [check] (1) Using a scale from 1 (highly digestible) to 4 (indigestible). Table 4-2 Forage carbohydrates as identified in the Van Soest procedure Relative ADF Component Digestibility (1) ADF NDF lignin Sugar 1 Starch 1 Hemicellulose 2 [check] Cellulose 3 [check] [check] Lignin 4 [check] [check] [check] ADF: Acid detergent fiber; NDF: Neutral detergent fiber. (1) Using a scale from 1 (highly digestible) to 4 (indigestible). Table 4-3 Carbohydrate fractions in feedstuff analysis NSC NFC ADF NDF Starch [check] [check] Sugars [check] [check] Organic acids [check] [check] Pectin [check] Hemicellulose [check] Cellulose [check] [check] Lignin [check] [check] Table 4-4 Carbohydrate fractions in various feedstuffs % of Dry Matter Feedstuff NSC NFC ADF NDF Legume hay 27.4 27.7 32.5 41.2 Grass hay 15.4 16.0 38.7 64.8 Legume silage 24.1 19.7 35.8 45.0 Grass silage 19.1 14.0 38.7 59.4 Corn silage 37.4 38.5 25.9 46.0 Citrus pulp 59.4 59.3 25.2 22.3 Almond hulls 46.6 48.1 28.2 35.3 Corn grain ground 68.7 67.5 3.4 13.1 Hominy feed 63.0 64.6 5.6 18.8 Barley grain 60.5 59.9 7.3 21.2 Oat grain 47.5 48.7 13.4 29.5 Wheat grain 64.8 64.5 4.8 15.8 Wheat middlings 33.5 33.0 11.8 38.2 Whole cottonseed 2.0 2.6 40.3 51.0 Bakery waste 57.3 58.7 5.3 13.6 Distillers dried grains 21.4 17.4 19.1 38.7 SBM 49% 29.3 27.7 5.8 10.5 Soybeans, heated 17.2 21.8 10.7 17.6 Soybean hulls 15.9 16.0 45.3 60.6 Peanut meal 19.2 18.3 13.9 25.6 Canola meal 23.2 23.8 19.2 28.6 Blood meal 0 0 0 0 Feather meal 0 2.4 0 0 Fish meal 0 8.1 0 0 NSC: Nonstructural carbohydrate; NFC: Nonfiber carbohydrate. ADF: Acid detergent fiber. NDF: Neutral detergent fiber. NDF and NSC values taken from Northeast DHIA, 1995. NFC values calculated from values from same source. Corn grain ground values (NSC, NFC, NDF) taken from Miller and Hoover, 1998. ADF value taken from Dairy NRC, 2001.
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|Author:||Tisch, David A.|
|Publication:||Animal Feeds, Feeding and Nutrition, and Ration Evaluation|
|Date:||Jan 1, 2006|
|Previous Article:||Chapter 3 Feedstuffs.|
|Next Article:||Chapter 5 Dietary energy.|