Forage Quality

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Forage Quality

• Forage Crops 4310

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Many ways to assess forage quality

• Human eye
• Laboratory
• Animal acceptance and performance

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Palatability

• In general, animals select the best plant
• But, not always true

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Palatability is affected by

• Texture
• Aroma
• Succulence
• Leafiness
• Fertilization
• Dung pats
• Urine patches
• Sugar content
• Etc.

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How much weight should palatability carry?

• Probably not much!
• Fescue not particularly palatable, but is the
  backbone of our grazing economy

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Ruminant Digestion

• Cattle are able to use low-quality forages to
  produce a high-quality source of vitamins,
  minerals, energy protein in the form of meat
  milk
• This is because they are ruminants
• Microbes in their digestive system ferment
  cellulose which non-ruminants (humans, pigs) do
  not have

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Ruminant Digestion

• Main source of energy
• Humans - glucose
• Cattle - volatile fatty acids (VFA)
• The compartments of the ruminant digestive system
  are
• Rumen
• Reticulum
• Omasum
• Abomasum

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Ruminant Digestive Tract
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Horse digestive tract
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Comparative Capacity of the GI Tractof Different
Species
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FORAGE PREFERENCE BY HERBIVORES
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HOURS SPENT GRAZING / BROWSING PER DAY
C Cattle S Sheep G Goats H Horses
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Forage Composition

• Plants, as fed, in pasture are 70 90 water.
  Silage is typically 55 65 water. Hay is
  around 10 15 water. But we often express
  forage analysis on a dry matter basis
• All requirement tables (next chapter) are
  presented on dry matter basis
• Converting to dry matter basis allows more
  accurate comparison of feedstuffs

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Converting to dry matter basis

• Divide by dry matter (DM) percentage
• Example problem Hay is 9 crude protein (cp) on
  as fed basis and corn silage is 4 cp on same
  basis. Hay is 90 DM and silage is 35 DM.
  Which is really higher in cp (on dry matter
  basis)?

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Converting to dry matter basis

• Nutrient on DM Basis Nutrient on AF
  Basis x 100
• DM
• Hay CP on DM Basis (9 90) x 100
  10
• Silage CP on DM Basis (4 35) x 100 11.4

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Two basic forage constituents

• Cell contents (non-structural) protein, sugar
  and starch highly digestible
• Structural cellulose, hemi-cellulose and lignin
  vary in digestibility

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Protein

• Presented as Crude Protein N x 6.25
• Plant cell walls contain up to 40 of the
  protein, much of which is not available to the
  animal
• Other factors affecting protein availability
  crop species, stage of maturity at harvest

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Protein

• Basics
• The major component of muscle, hair, hooves,
  skin, internal organs and body chemicals
• Composed of smaller units, Amino Acids
• Beef rations balanced for protein rather than
  individual amino acids
• Rumen microbes digest most of protein and change
  it to microbial protein

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Protein

• (continued)
• Referred as Crude Protein (CP) - a reliable
  estimate of the protein content
• Another method of expressing protein
• Metabolizable Protein (MP) system
• Degradable Intake Protein (DIP)
• Undegradable Intake Protein (UIP)
• The MP system takes into account how protein is
  used by both the animal and the microbes in the
  rumen

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Energy

• Basics
• Nutrient that is provided in largest quantity and
  is fuel for the body usually most limiting in
  forages
• Total Digestible Nutrients (TDN) is most often
  used as an energy measure
• Additional terms to describe efficiency
• Digestible Energy (DE)
• Metabolizable Energy (ME)
• Net Energy (NE)

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More on Energy

• Non-structural carbohydrates in forages are
  readily digested
• Ruminants and horses have ability to digest
  cellulose and hemicellulose, but not lignin. As
  lignin increase, digestibility decreases.
• White clover, birdsfoot trefoil, small grains are
  low in lignin
• Alfalfa increases in lignin with age
• Bermudagrass lignifies fairly quickly

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Factors affecting plant quality

• Plant species
• Plant part
• Climate
• Stage of maturity
• Fertilization
• Diurnal Fluctuations
• Other (rain on hay, poor hay storage)

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Plant SpeciesWhich is more digestible

• Cool season grasses gt Warm season
• Cool season annuals gt Cool season perennial
• Legumes gt grasses
• Dallisgrass gt Bermudagrass

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Quality Comparisons plant parts

• Leaves gt Stems
• Young leaves gt Old leaves
• Healthy plants gt Diseased plants

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Climate

• Spring plants gt summer plants
• High Temperature increase lignification, so
  decreases quality
• Tannin also increases with hot weather in Sericea

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Stage of maturity

• In general, as plants mature, quality declines
  (see following slide)
• Exception White clover holds quality due to lack
  of true stems

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Plant growth rate at various stages of growth
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Tall fescue protein content as plants mature
seedhead production
May
June
July
Bates. 2000. Unpublished data. Plateau Experiment
Station.
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Diurnal fluctuations

• Soluble Carbohydrate levels vary high in late
  afternoon, low in early morning
• Hay cut in late afternoon will be higher in
  soluble carbs.
• Cattle do 60 of grazing in late afternoon
  early night

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Methods of measuring forage quality

• Visual
• Neutral Detergent Fiber and Acid Detergent Fiber
• In-vitro fermentation
• Near infrared reflectance spectroscopy (NIRS)

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Relative Feed Value

• A percentage figure that compares hay to Alfalfa
  harvested at full bloom at 100
• Variables include DDM from ADF and DMI from NDF
• Good predictor of animal performance because it
  considers both energy and intake

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Visual Evaluation

• Stage of Harvest
• Leafiness
• Color
• Odor
• Softness
• Penalties