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ANALYTICAL AND BIOLOGICAL DATA 3 ANALYTICAL AND BIOLOGICAL DATA SOURCE OF DATA Most of the data was compiled by the International Feedstuffs Institute at Utah State University, Logan, Utah. However, data from many individuals in both industry and public institutions have been incorporated. To assist in making the tables more useful, source data values were generated for missing data for some attributes by using regression equations as outlined below. In some cases, such as for stage of maturity of forages, data were estimated from similar feeds. When reasonable values could not be estimated or were insignificant in formulating animal diets, the spaces were left blank. Data in this report may differ from those in various other NRC reports because of the reasons given above, but the values in the tables represent the best judgment of the Committee on Animal Nutrition's Subcommittee on Feed Composition. VARIATION IN DATA Feedstuffs are not of constant composition, and individual feed samples may vary widely from the values set forth in these tables. The variation is caused by such factors as variety, climate, soil, and length of storage. Actual analysis should be obtained and used wherever possible. Often, however, it is either impossible to determine actual composition or there is insufficient time to obtain such analysis, making tabulated data the next best source of information. When tabulated data are used, it should be understood that feeds do vary in their composition and, therefore, the values should be used as guides. Organic constituents (e.g., crude protein, cell wall constituents, ether extract, amino acids) can vary as much as Â±15 percent, the inorganic constituents as much as Â±30 percent, and the energy values as much as Â±10 percent. See Table 9 for weight-unit conversion factors. DRY MATTER Typical dry matter values are shown; however, the moisture content of feeds varies greatly and the dry matter content may be the main reason for variation in the composition of feedstuffs on an âas-fedâ basis. Because dry matter can vary greatly and because one of the factors regulating total feed intake is the dry matter content of feeds, diet formulation on a dry matter basis is preferred over using the as-fed basis. Dry matter values of nutrient attributes may be converted to an as-fed basis by simply multiplying the dry matter by the nutrient values and dividing by 100. ENERGY VALUE OF FEEDS Energy values of feeds are frequently influenced by interactions with other feeds, by level of feed intake, and by other management factors. The values listed in this publication are, therefore, a guide in ânormalâ feeding and management situations and should not be considered to be an inflexible constant. Because of the effect of level of intake on digestibility of feeds, the total digestible nutrients (TDN), digestible energy (DE), and metabolizable energy (ME) values of feeds for ruminants have been listed as appropriate for animals in production. Energy values for ruminants, horses, and swine include TDN, DE, and ME. For ruminants, net energy values are given for maintenance (NEm), gain (NEg), and lactation (NEl). For poultry, energy values include nitrogen-corrected metabolizable energy (MEn), true metabolizable energy (TME), and net energy for production (NEp). A discussion of these net energy values may be found in individual NRC nutrient requirement reports. Details of methods of calculating individual energy values are as follows (all calculations are done on the dry matter basis): Energy Values of Feeds for Ruminants Total Digestible Nutrients Total digestible nutrients for ruminants was calculated from: a. average TDN for cattle and sheep b. or from digestion coefficients for cattle and sheep as: digestible protein (%) Ã1.0 digestible crude fiber (%) Ã1.0 digestible nitrogen-free extract (%) Ã1.0 digestible ether extract (%) Ã2.25 TDN (%) TOTAL Digestible Energy Digestible energy for cattle and/or sheep was calculated by using the formulas of Crampton et al. (1957) and Swift (1957): DE (Mcal/kg DM)=TDN for cattle and sheepÃ0.04409. Metabolizable Energy Metabolizable energy was calculated from DE. These values were used to calculate NEm and NEg from the following formula: (Mcal/kg )=0.82Ã (Mcal/kg )
ANALYTICAL AND BIOLOGICAL DATA 4 ME DM DE DM For the ME shown in the table, the following formula was used (Moe and Tyrrell, 1976; NRC, 1981): ME (Mcal/kg DM)= 0.45+1.01 DE (Mcal/kg DM) Net Energy Net energy for finishing cattle was calculated by equations developed by Garrett (1977): NEm (Mcal/kg DM) =1.115 0.8971 ME+0.6507 ME2 0.1028 ME3+0.005725 ME4 NEg (Mcal/kg DM) =3.178 ME 0.8646 ME2 +0.1275 ME3 0.00678 ME4 3.325 Net energy values for NEl were calculated by using the formula of Moe and Tyrrell (1976): NE1 (Mcal/kg DM)= 0.12+0.0245 TDN (% of DM). Energy Values of Feeds for Horses and Swine Total Digestible Nutrients Total digestible nutrients for horses and swine were calculated from: a. average TDN b. or from digestion coefficients as: digestible protein (%) Ã1.0 digestible crude fiber (%) Ã1.0 digestible nitrogen-free extract (%) Ã1.0 digestible ether extract (%) Ã2.25 TDN (%) TOTAL c. DE for horses (Fonnesbeck et al., 1967; Fonnesbeck, 1968): TDN%=20.35ÃDE (Mcal/kg)+8.90 (This formula was used only for class 1 feeds.) d. TDN for horses and swine was not calculated from ME e. or from regression equations (Harris et al., 1972). Digestible Energy Digestible energy for horses and swine was calculated from: a. the average digestible energy in kcal/kg or Mcal/kg b. DE (kcal/kg DM)=Gross Energy (kcal/kg)ÃGross Energy digestion coefficient c. TDN for horses (Fonnesbeck et al., 1967; Fonnesbeck, 1968): DE (Mcal/kg DM)=0.0365ÃTDN%+0.172 d. TDN for swine (Crampton et al., 1957; Swift, 1957) DE (kcal/kg DM)=TDN%Ã44.09 Metabolizable Energy Metabolizable energy for horses, swine, and poultry was calculated from: a. the average metabolizable energy in kcal/kg or Mcal/kg b. the average true metabolizable energy (TME) in kcal/kg for poultry (Sibbald, 1977) c. the average nitrogen corrected metabolizable energy (MEn) for poultry (National Research Council, 1966) d. ME for horses (Mcal/kg DM)=0.82ÃDE (Mcal/kg DM) e. ME for swine (Asplund and Harris, 1969) ME (kcal/kg DM)=0.96 (0.00202Ãcrude protein %) ÃDE (kcal/kg DM) PROTEIN Crude Protein The crude protein value shown in these tables is the nitrogen value times 100/16 or 6.25, because protein on the average contains 16 percent nitrogen. To determine the apparent protein content of a given feed more accurately, conversion factors for that feed can be used; however, these factors have been determined for only a few feeds (Jones, 1941). Crude protein values do not distinguish between true protein and nonprotein nitrogen content of feeds. Digestible Protein Digestible protein was not included in Table 1 but it can be calculated for each kind of animal as follows: a. or b. By equations developed for six animal species and four feed classes by Knight and Harris (1966).
ANALYTICAL AND BIOLOGICAL DATA 5 Because of the large contribution of body protein to the apparent protein in feces (metabolic fecal protein), the digestible protein value for a given feed can be misleading (Preston, 1972). The digestible protein content for the total diet can be more accurately calculated from the crude protein content of the diet using the equations of Knight and Harris (1966). PLANT CELL WALL CONSTITUENTS INCLUDING CRUDE FIBER Total insoluble dietary fiber is represented by cellulose, hemicellulose, and lignin. Plant cell walls also contain pectins, which are largely removed with neutral detergent, and protein and mineral components. Some protein fractions are very insoluble and are the slowest digesting nitrogen fraction of forages (Pichard and Van Soest, 1977). Plant cell wall analysis quantitatively includes the truly indigestible lignified portion of the feed and is, therefore, the theoretical replacement for crude fiber. But while cell wall content is the best predictor for digestibility in nonruminants (Henry, 1976), it is more clearly related to intake in ruminants than to digestibility (Table 10). Acid detergent fiber and lignin are better indicators of digestibility for ruminant diets. Forages were once defined as feeds containing more than 18 percent crude fiber. But it is recommended that the use of crude fiber as a means of classification be abandoned in favor of using the percentage of cell wall constituents. Hence, forages are defined as leaf and stem portions of plants with more than 35 percent cell wall constituents in the dry matter. In addition, forages can be further characterized by the percentages of their cell wall components (Table 11), which is the recommended basis for a new hay grading system (Rohweder et al., 1978). This system recognizes that forages vary in composition according to conditions of growth: Those forages growing in warmer and wetter climates tend to be higher in lignin content. Warm-season grasses are also higher in cell wall content and often lower in protein at comparable stages of growth than are cool-season or northern grasses. Northern alfalfa tends to have lower lignin and protein and higher cell wall content than southern alfalfa. Most forages grown in cool conditions tend to be more digestible. In temperate regions, digestibility of pasture in the spring and summer is lowest at the hottest period. Autumn and forage maturity are often associated with an increase in nutritive value (Van Soest et al., 1978). An attempt has been made to recognize the environmental and regional variables affecting forage composition (Table 1). Comparative data are given for alfalfa, Bahiagrass, Bermudagrass, fescue, pangolagrass, and sorghum. Cellulose The most often considered carbohydrate of the fiber fraction is cellulose, which is a 1, 4- -glucan. It is the most insoluble fraction of the cell wall and is seldom obtained pure even in chemical isolation. Most celluloses contain cuticular fractions and about 15 percent arabinoxylan, properly a hemicellulae. Most values for cellulose have been determined by the Crampton method (Crampton and Maynard, 1938) or the permanganate procedure of Van Soest and Wine (1968), which are assumed to be interchangeable. Hemicellulose The noncellulose portion of cell wall carbohydrate is a complex substance containing a variety of linkages and sugars. One main fraction in grasses and legumes is an arabinoxylan with some glucuronic acid. Hemicellulose is not a uniform fraction and is combined with lignin in the encrusting matrix of the recovered part of the cell wall. The percentage of hemicellulose is much greater in grasses than in legumes. Values in the tables have been estimated separately for cell wall and acid detergent fiber contents. Lignin The main organic noncarbohydrate portion of cell wall is crude lignin, composed of true lignin, cutin, Maillard polymers, and amino-protein complexes. True lignin is a phenylpropanoid polymer that provides the crosslinked three- dimensional structure that gives the plant cell wall its rigidity and resistance. It is the primary factor that reduces the digestibility of forages, although there are other contributors, such as silica in rice straw and hulls. The cuticular fraction is also resistant to digestion; it occurs in the skin surface of plants and in barks and seed hulls. It is a polymerized lipid of different constituents than lignin. The Maillard polymer is formed upon heating and drying as the result of heat damage. It has the properties of lignin and is formed from a one-to-one condensation of amino acid from protein and a sugar unit from hemicellulose. It is indigestible and accounts for the lower protein digestibility of heated feeds. This aspect of quality is not shown in the tables. Heating in silages, hays, and pelleted feeds is highly variable and it is recommended that the availability of feed nitrogen be assayed by means of acid detergent fiber insoluble nitrogen (Goering et al., 1972). PROXIMATE ANALYSIS AND CRUDE FIBER The old system of feed analysis was the proximate system in which the dry matter is divided into ether extract (lipid) protein, ash, crude fiber, and nitrogen-free extract (NFE), the NFE content being determined by subtraction of the others. The principal problem of this system is the distribution of the organic nonlipid, nonprotein fraction between crude fiber and NFE, which fails to provide a meaningful separation of the carbohydrates according to their nutritive value. Crude fiber analysis fails to recover any one of the cell wall components. About 50â90 percent of the lignin, 85 percent of the hemicellulose, and 20â50 percent of the cellulose are dissolved in the determination of crude fiber content. These then are included in the calculated NFE, which is supposed to represent the available and easily digestible carbohydrates of the feed. In about 30 percent of the analyses, NFE is determined to be less digestible than the crude fiber, primarily because most of the very indigestible lignin is included in the NFE. Because of
ANALYTICAL AND BIOLOGICAL DATA 6 this inaccuracy nitrogen-free extract is not reported in the tables and its use as a determinant of nutritive value is discouraged. Calculation of NFE from acid detergent fiber (lignocellulose) or cell wall content is also discouraged, because this also perpetuates inaccuracies in regard to the NFE calculated by difference. ETHER EXTRACT The lipid portion of plants, which is included in the ether extract fraction, varies depending upon the plant part. True fat and oil (triglycerides) occur only in storage organs such as seeds; the leaves and stems are virtually free of triglycerides. The fatty acid fractions of leaves and stems are contained in galactolipids of lower energy content than triglycerides. Leaves and stems also contain waxes, chlorophyll, essential oils (esters and terpenes), pigments, saponins, flavonoids, isoflavonoids, and alkaloids, most of which have no nutritive value or inhibit the utilization of feed. Utilizable fatty acids constitute no more than 50 percent of forage lipids, but are the main component of seeds and grain by-products. LINOLEIC ACID Values for linoleic acid, an essential fatty acid, are shown in Table 5, where the information was available. The major sources of linoleic acid in feedstuffs are the vegetable oils. Corn oil and cottonseed oil are approximately 50 percent linoleic acid; safflower oil is 75 percent linoleic acid. Yellow corn is the major source of linoleic acid in many feed formulas. MINERALS Values for the important mineral elements are shown in Table 2. Several other minerals known or thought to be required are not listed because of paucity of compositional data. The values shown are the total percentage or weight of the mineral present. The availability (digestibility) of minerals in feedstuffs varies considerably and can be an important factor in the value of a feed as a source of a particular mineral for animals. The composition of mineral supplements is shown in Table 6. VITAMINS Values for some important vitamins are shown in Table 3. Xanthophyll, which is useful in poultry diets to provide yellow coloration in egg yolks and yellow skin coloration, is listed in this table although it is not a vitamin. Carotene (provitamin A) values are provided but vitamin A values are not, because species convert carotene to vitamin A at different rates (see Table 12). Vitamin A standards are as follows: The international standard for vitamin A activity as related to vitamin A and beta-carotene are as follows: 1 IU vitamin A =1 USP unit =vitamin A activity of 0.300 microgram crystalline vitamin A alcohol =vitamin A activity of 0.344 microgram vitamin A acetate =vitamin A activity of 0.550 microgram vitamin A palmitate 1 IU vitamin A =0.6 microgram beta-carotene 1 mg beta-carotene =1,667 IU vitamin A. International standards for vitamin A are based on the utilization of vitamin A and beta-carotene by the rat. Because the various species of animals do not convert carotene to vitamin A in the same ratio as rats, it is suggested that conversion rates in Table 12 be used. A detailed discussion of the variations in vitamin activity and nomenclature is beyond the scope of this publication. Compounds with different levels of vitamin D, E, and K activity are known to occur in nature. The complexity of vitamin nomenclature precludes incorporating variations in a single vitamin table. For instance, folacin and folic acid are frequently used interchangeably, but folacin is the correct term for describing the activity of this vitamin in feedstuffs. Likewise, vitamin B6 refers to a complete class of three compounds; whereas, pyridoxine refers specifically to the primary alcohol form.