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Bruce L. Welch Chapter 14 Nutritive Principles in Restoration and Management Most range management or revegetation programs are aimed at providing forage to support the needs of range animals. Among these needs are supplying the nutrients required to drive the physiological processes of the animal body. One major principle in this report is that there is no “perfect forage species” that will supply all the nutrients needed by any range animal for all seasons. The best approach to range management or revegeta- tion is to supply a diversity of palatable shrubs, forbs, and grasses. Major topics to be discussed are (1) nutrient require- ments of range animals, (2) judging the nutritive value of range plants, (3) factors affecting the nutritive value of range plants, and (4) seasonal nutritive value of range plants. USDA Forest Service Gen. Tech. Rep. RMRS-GTR-136. 2004 175 Chapter 14 Nutritive Principles in Restoration and Management Nutrient Requirements of Range Table 1—Daily dry matter consumption by selected range animals. Data expressed as pounds of dry matter Animals _______________________ consumed on a daily basis and as a percentage of live weight (Halls 1970; National Academy of Sci- It is a fundamental principle that effective range ences 1975, 1976, 1977, 1978, 1982, 1984). management or revegetation programs rest on know- ing the nutritive requirement of the target animal. Dry matter The nutrient needs of range animals can be divided Animal Activity Weight Per day Live weight into five classes: dry matter intake, energy-producing - - - - - Lbs - - - - - - Percent compounds, protein, minerals, and vitamins. Sheep Maintenance 110 2.2 2.0 (ewes) 132 2.4 1.8 Dry Matter 154 2.6 1.7 176 2.9 1.6 Intake of dry matter by range animals varies accord- Last 6 weeks 110 3.7 3.3 ing to the weight and activity of the animal. Greatest of gestation 132 4.2 3.2 consumption of dry matter, with weight held constant, 154 4.6 3.0 occurs with lactation, followed by growth, as a percent 176 4.8 2.8 of live range animals. This is of considerable impor- Lactation 110 5.3 4.8 tance to the range manager when it comes to calculat- 132 5.7 4.3 ing carrying capacity. Dry matter intake of selected 154 6.2 4.0 range animals is tabulated in table 1. 176 6.6 3.7 Growth 66 2.9 4.3 Energy-Producing Compounds 88 3.1 3.5 110 3.3 3.0 From a quantitative point, energy-producing com- 132 3.3 2.5 pounds make up the single largest class of nutrients Cattle Maintenance 881 13.4 1.5 needed by range animals. A lack of sufficient energy is 1,102 15.9 1.4 probably the most common manifestation of nutri- 1,323 18.3 1.4 tional deficiency in range animals (Dietz 1972). Range animals can derive energy from a variety of com- Gestation 881 16.5 1.9 1,102 19.0 1.7 pounds including sugars, fats, pectins, starch, and 1,323 21.4 1.6 protein. In ruminants and other range animals that can support fermentation digestion, energy can be Lactation 881 23.8 2.7 1,102 26.0 2.4 derived indirectly from cellulose and hemicellulose. 1,323 28.4 2.1 To understand the energy requirements of range animals, the range manager or revegetation specialist Growth 661 19.4 2.9 needs first to understand the various terms that are 881 24.3 2.8 1,323 26.5 2.0 used to express the energy requirement. Energy requirements of range animals are expressed Horses Maintenance 16.4 in several forms such as total digestible nutrients, Gestation 16.4 Lactation 21.5 digestible energy, metabolizable energy, and net en- Growth 13.2 ergy. Total digestible nutrients, a noncaloric measure- ment, is the sum of all the digestible organic matter Deer Maintenance 2.2 Gestation 2.5 (crude protein, crude fiber, nitrogen-free extract, and Lactation 3.0 crude fat) in a forage. Because fat supplies 2.25 times more energy than protein or carbohydrates, the fat Elk Maintenance 9.6 content is multiplied by this 2.25 energy factor to (mature) calculate this principal measurement (table 2). The total digestible nutrients requirement of an animal is expressed as kg per animal per day or as percent of the from the body from the digestible energy of the range diet. For range managers or revegetation specialists forage. Net energy then is calculated by subtracting the latter expression is the most useful. the calories used to produce body heat from metaboliz- Digestible energy, a caloric measurement, is calcu- able energy. Net energy thus represents the amount of lated by subtracting the caloric content in the feces energy an animal has for maintenance and production. from the caloric content of the range forage. The caloric The relationship of these three caloric energy mea- content of a range forage is often called gross energy. surements was demonstrated (fig. 1). Range animal In turn, metabolizable energy is calculated by sub- requirements for any one of these measurements is tracting the caloric content in the urine and gases lost expressed as megacalories per animal per day or as 176 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-136. 2004 Chapter 14 Nutritive Principles in Restoration and Management Table 2—How the amount of digestible nutrients are calculated for a attempted to express the energy requirements of range hypothetical range forage. animals in terms of in vitro digestibility (table 4). Total nutrients Digestion Digestible Maintenance was set at 50 percent in vitro digestibil- Nutrient in 100 kg coefficients nutrients ity with all other activities adjusted accordingly (Ammann and others 1973). kg - - - - - - Percent - - - - - - Crude protein 9.0 50.0 4.5 Crude fiber 30.0 40.0 12.0 Protein Nitrogen-free extract 50.0 50.0 25.0 Crude fat 11.0 50.0 (2.25) 12.4 Protein in animal bodies makes up a large chemi- Total digestible nutrients 53.9 cally related, but physiologically diverse, group of compounds. Protein is the major organic compound of the organs and soft tissues of the animal body. All proteins are made from a common set of building megacalories per kg of dry matter. The latter expres- blocks known as amino acids. It is the sequence of sion is the most useful for range managers or revegeta- these amino acids along the protein molecule that tion specialists. gives a particular protein its character which, in turn, Energy needs of range animals vary according to determines its function. Proteins are the chief compo- weight and activity (lactating, fattening, growing, nent in nearly all body parts including skeletal muscle gestation). Larger animals require more kilograms of for external movement; smooth and cardiac muscle for total digestible nutrients per day for a given activity internal movement; tendons and ligaments for tying than smaller animals, yet when total digestible nutri- together body parts; organs and glands such as the ents is expressed as a percent of the diet the percent- stomach, eyes, pituitary, and skin with its covering of age is the same. This is due to differences in dry matter hair; and other structures including hemoglobin, cyto- intake. Thus a large animal extracts more kilograms chromes, and membranes. Enzymes are also an im- per day of total digestible nutrients than a smaller portant group of proteinaceous compounds that pro- animal eating the same forages. Similarly, a lactating vide the framework in which the chemical reactions of female requires more energy than a nonlactating fe- the body take place. male of similar weight. On a constant weight basis, Because of the involvement of protein in so many lactation requires the greatest amount of energy bodily functions, the animal body needs a liberal and followed by fattening, growing, gestation, and mainte- continuous supply of protein. Like energy, the protein nance. Table 3 lists the energy requirements of se- requirement of range animals varies according to the lected range animals. Unfortunately, the total digest- weight and activity of the animal. From a qualitative ible nutrients content or amount of metabolizable point, the protein requirement varies according to the energy is unknown for many range forages. More type of digestive system operating in the range ani- information is expressed as in vitro digestibility. I have mal. For ruminants and other range animals that can support fermentation digestion, including horses, rabbits, burros, and sage-grouse, the quality of the protein—that is the actual amino acid makeup—is not important, only the quantity. The microorganisms Gross Energy responsible for the fermentation also manufacture Energy loss needed amino acids from plant protein and organic in feces nitrogen compounds. Protein requirement of range animals is expressed Digestible Energy either in terms of digestible protein, or as crude (some- Energy loss Energy lost times called total) protein. The requirement values in in gases in urine the diet are expressed as grams per day or as a Metabolizable Energy percentage. For range managers or revegetation spe- cialists, the term crude protein as a percent in the diet Energy lost as is the most useful. As with energy, the greater the body heat weight of the animal, the higher the protein require- Net Energy ment, assuming similar body activity. Because larger range animals consume more dry matter, their higher Energy for Energy for protein requirement can be met by consuming diets production maintenance with the same percentage of protein as smaller ani- mals. The difference is in the amount of dry matter Figure 1—Relationship of gross, digestible, eaten. Protein requirement varies also according to metabolizable, and net energy.

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