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Week 4

Roughages

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Introduction to Roughages

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  • In U.S., over 50% of feedstuffs fed
  • Plant-based feedstuffs
  • Terminology
    • Forage and herbage
      • Plant materials available for consumption by animals
    • Roughages
      • Higher fibrous carbohydrate content compared to forages
    • Terms used interchangeably
  • National Research Council
    • Minimum CF at 18%
    • Maximum TDN at 70%
  • Functions
    • Provide nutrients
    • Maintain and optimize efficiency of GI tract
      • Maintain structure, activity, and microbial population
    • Use of earth’s resources
      • Roughages minimal value to humans
      • Consumed by selected species
      • Conversion of low-quality to high-quality products
      • End-products used by humans
  • States
    • Fresh
    • Dried
    • Ensiled
  • Types
    • Grazed
      • Pasture and range
    • Preserved
      • Hay and silage
    • Crop residues and by-products
      • Straw, stover, and hulls
  • Note: significant exceptions to following generalizations exist
  • Description
    • Bulkier feedstuffs; less mass per unit volume
    • Low digestible energy
    • Low digestibility of other nutrients
    • High in fibrous carbohydrates
      • Primarily present in cell wall
      • Associated with structural components
        • Structural carbohydrates
    • Potentially high in lignin
  • Nutritional analyses of fibrous carbohydrates
    • Crude fiber
      • Cellulose and portion of hemicellulose
    • ADF
      • Cellulose and lignin
    • NDF
      • Hemicellulose, cellulose, and lignin
    • Figure 8.1 -  Relationship between components of cell wall and analyses
    • Figure 8.1 - Relationship between components of cell wall and analyses

  • Additional components
    • Cell contents
    • Nonfibrous carbohydrates
      • Simple sugars
        • Fructose, glucose, and sucrose
      • Starch
      • Fructosans
    • Protein
      • True protein
      • NPN compounds
      • Varies
        • Legume content greater than grasses
    • Minerals
      • Varies by roughage and mineral content of soil
        • Legumes higher Ca and Mg contents
      • Compared to concentrates
        • Higher in Ca, K, and microminerals
        • Moderate to low in P
    • Vitamins
      • Compared to concentrates
        • Higher in fat-soluble vitamins
      • Good source of B-complex vitamins
    • Presence of antinutritional factors
      • Examples: alkaloids, cyanogenic glycosides, toxic amino acids, and/or mycotoxins
  • Nutritional value
    • Varies
      • Plant species
      • Proportion of cell contents to cell walls
      • Extent of lignification
    • Most may be effectively incorporated in at least one type of ration
      • Match nutrient requirements with nutrient content
      • Appropriate processing and supplementation
  • Feeding high-energy feedstuffs with roughages
    • Introduction
      • Rumen microbial enzymes require for roughage digestion
      • Rumen microbial population dependent on feedstuffs
      • Diet composition influences digestion of roughages
    • Feeding high-energy feedstuffs negative associative effect on utilization of roughages
      • Digestion of roughages
        • Cellulolytic species
        • Acetate
          • Weak acid
      • Digestion of high-energy feedstuffs
        • Propionate
          • Relatively strong acid
        • Lactate
          • Strong acid
        • Lower resultant pH
          • pH lower than 6.0 inhibits cellulolytic species
          • Decreases utilization of roughages
    • Strategies to increase utilization
      • Buffers
      • Increasing particle size of roughage
      • Reducing rate of fermentation of high-energy feedstuff
  • Feeding
    • Dependent on GI tract
      • Microbial enzymes required for digestion of fibrous carbohydrates
      • Dependent on site and extent of microbial fermentation in GI tract
    • Added to rations of herbivores
      • Ratio dependent on animal species and class and cost
    • Ruminants
      • High utilization efficiency
      • Source of fibrous carbohydrates
      • Generally, added to rations
    • Horses
      • Lower utilization efficiency
      • Cecum
        • Posterior to primary site of absorption
        • Coprophagy – consumption of feces
          • Improve utilization efficiency
      • Used in rations
    • Swine and poultry
      • Low utilization efficiency
      • Limits use in rations

 

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