Week 4

Roughages

Chemical Composition of Herbage

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• Chemical composition and nutritional value of forage
• Complex
• Influenced by number of factors
• Primarily plant species, environmental and soil conditions, and/or stage of maturity
• Nitrogen component
• Expressed as CP
• Measures protein and nonprotein nitrogen compounds
• Factors influencing CP
• Plant species, environmental and soil conditions, and stage of maturity
• Legumes higher than grasses
• Legumes
• Range: 15-30% (DM basis)
• Cool-season grasses
• Range: 10-20% (DM basis)
• In specific situations, may be lower or higher
• For grasses, CP content dependent on nitrogen fertilization
• True protein is 75-85% of nitrogen
• As matures, portion of nitrogen as true protein increases
• Nonprotein nitrogen compounds
• More than 200 identified in forages
• Factors influencing NPN content
• Soil and environmental conditions and plant species
• Legumes higher than grasses
• Nutritional value of nonprotein amino acids
• For nonruminants, app. half value for protein amino acids
• For ruminants, similar in nutritional value to amino acids in protein molecules
• Carbohydrate content
• Nonstructural carbohydrates
• Readily available carbohydrates
• Mono and disaccharides
• Relatively low
• In general, less than 8% (DM basis)
• Primarily glucose, fructose, and sucrose
• Polysaccharides
• Primarily starch and fructosans
• Stored energy for plant
• Legumes
• Sucrose and starch
• Warm-season grasses
• Starch
• Cool-season grasses
• Fructosans
• Cool-season grasses and temperate legumes harvested at similar maturities, similar TNC content
• Factors influencing TNC content
• Plant species, environmental conditions, and soil fertility
• Correction to text, nonstructural carbohydrate content highest at end of the day
• To increase NSC content at harvest, harvest at end of daylight hours
• Structural carbohydrates
• Polysaccharides
• Three classes
• Pectic substances
• Noncellulosic polymers
• Hemicellulose
• Digestible only by microbial enzymes
• Cellulose
• Digestible only by microbial enzymes
• Factors influencing structural carbohydrate content
• Species and environmental conditions
• As plants mature
• As legumes mature
• Increase in stem cellulose
• As grasses mature
• Increase in stem cellulose and hemicellulose
• Lipids
• In leaf tissue
• Content is 3-10%
• Decreases with maturity
• Primarily galactolipids and phospholipids
• Linolenic acid is 60-75% of fatty acids
• Upon disruption of surface, unsaturated lipids susceptible to oxidative processes
• Organic acids
• In general, not reported specifically
• In general, included with other components
• NFE portion of proximate analysis
• Cell contents or solubles of detergent fiber system
• Most nonvolatile
• Range: 2-8% (DM basis)
• Factors influencing organic acid content
• Plant species, maturity, and fertilization
• Palatability of feedstuff
• Minerals
• Table 7-7 on page 126 of text – Range and typical mineral concentration for grasses and alfalfa
• Does not include all macro and microminerals in forages
• General
• Grasses and legumes high in K
• Legumes higher contents of Ca, Mg, S, and Cu than grasses
• Grasses higher contents of Mn and Zn
• Grasses and legumes moderate to low in P
• Variable
• Factors influencing mineral content
• Plant species and soil and environmental conditions