Unit 2: Evaluating Feedstuffs for Farm Livestock

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Unit 2 Evaluating Feedstuffs for Farm Livestock
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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Unit 2 Objectives
• Understanding of methods used to determine
  nutrient composition of feeds
• Knowledge of sample collection methods
• Identify and communicate how feed samples are
  reported
• Comprehension of how feedstuff digestibility is
  determined
• Understand various energy measurements and how
  they are used
• Physical and economical evaluation of feeds

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Analytical Methods for Nutrient Composition
• Three general types of methods can be used to
  determine effect of feedstuffs
• Chemical procedures
• Titration, colorimetry, etc.
• Biological procedures
• Feedstuff tested by a live animal (rat, chick)
• More accurate
• Much more tedious and expensive

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Microbiological procedures
• Tested w/ isolated bacteria
• Obtaining Samples for Analysis
• Key to reliable feed nutrient evaluation is a
  representative sample
• Identification
• Thoroughly identify the feed tested
• What might we include in our identification?
• Sampling
• Grains/Mixed Feeds
• Sacked feeds 2 samples/sack, 5-7 sacks, handful
  each

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Bulk Feeds 12 to 15 samples, widely separate
  locations for sampling (while delivered or fed,
  if possible)
• Mix samples in a clean pail, make sure feed
  doesnt separate, send a 1 or 2lb. sample to the
  lab
• Hay
• Use a core sampler
• Take a 12 15 core sample that will include
  stem and leaves
• 12 15 samples are needed to be accurate
  (1/bale)
• Try to get to middle of the stack if possible
• Grab Samples can be used, but accuracy is
  variable

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Haylage or Silage
• Upright silos collect during feedout, several
  small samples, mix together for one composite
• Pit/Bunker silos 4-5 grab samples from a fresh
  face, do not collect spoiled material, do not
  collect within 12-18 from edge
• Freeze if you are collecting over multiple days
• Refrigerate if you cant mail immediately (what
  happens if you dont do this?)
• Harvest Sampling
• Not recommended for any feed lt30 DM
• Same methods as discussed prior
• 12-15 samples, mix for one composite
• Mark different fields as feed is stored (plastic
  marker, oats, etc.)

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• General
• Not beneficial unless you are going to use in
  designing a feeding program
• Three benefits to using sampling for proper
  balance of feedstuffs 1) minimize protein
  supplementation and reduce cost, 2) can properly
  balance if a nutrient is being underfed, 3) can
  confirm that a factor other than feed is limiting
  production
• Proximate Analysis
• Most generally used chemical analysis to describe
  nutrient composition of feeds

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Dry Matter (DM)
• How do we determine DM content of a feedstuff?
• Can we do this ourselves?
• What is the benefit of knowing the DM content?
• Ash (minerals)
• Burned sample that removes all other nutrients
• Only inorganic residue remains
• May not be 100 accurate
• Crude Protein (CP)
• Digest to N through chemical process (Kjeldahl
  process)
• How do we determine CP content from N
  concentration?
• Does not distinguish between forms of N

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Ether Extract (Fat)
• Use ether to extract fat contents for 4 hrs
• Loss of wt fat content
• Includes some fats that are of no use to
  animals, so may not be 100 accurate
• CHO
• Crude Fiber (CF) remove water fat then
  through chemical rxn. to remove protein, sugar,
  and starch leaves cellulose, lignin, and
  minerals (how are the minerals removed?)
• Nitrogen-Free Extract (NFE) sugars and starches
  (maybe some hemicellulose lignin) not
  determined by an analysis 100 - water, ash,
  protein, fiber, fat

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• The Van Soest Method
• Focuses on forage fiber
• Divides fiber into digestible and indigestible
  fractions
• Extraction w/ detergents
• Predicts intake NDF index of gut fill
• Predicts digestibility ADF indicates forage
  digestibility
• Heat damaged forages can help determine the
  amount of protein unavailable in feedstuff. What
  level of unavailable begins to cause problems?

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Near Infrared Reflectance Spectroscopy
• Ability to sample quickly w/ little preparation
  (grinding) only uses one sample
• Can be completed in lt3 min.
• Analyze multiple components in one operation
• Measurements done by absorption/reflection of
  light
• Not accurate for minerals
• Expensive equipment, must be calibrated correctly
• Wet-chemistry analysis is more accurate
• Inexpensive

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Determination of Vitamins
• No routine analysis available to determine vit
  content
• Assays can be ordered to determine specific
  vitamins, if needed
• Determination of Energy
• Bomb Calorimeter
• Sample is burned in an oxygen atmosphere
• Liberated heat raises the temp of water
  surrounding the devise
• This temp increase is the basis for determining
  the energy concentration
• 1 cal heat required to raise 1g water 1º C

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Nutrient Expression
• DM basis
• Most accurate/common way to express nutrient
  levels
• Levels the playing field to compare feeds
• As-Fed basis
• Amount of nutrients contained in a feed as the
  animal would consume it
• Air-Dry basis
• Assumed to be 90 DM

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Lets practice some conversions
• Thumb rules
• Nutrient concentration should increase when
  converting to DM basis
• Wt. will decrease on DM basis
• Feeding Trials
• Can give information as to acceptance and
  performance of a feed
• Doesnt tell why a feed performed the way it did

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Digestion or Metabolism Trial
• Weakness of chemical analysis is that is doesnt
  take into account digestibility very accurately
• Steps of a digestion trial
• Proximate feed analysis to know what you start w/
• Feed a measured amount of feed, or feed at
  constant rate
• Collect fecal matter
• Proximate analysis on feces
• Difference is the apparent digestibility of the
  feed

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Can use markers or indicators to identify feeds
• Testing can be done in metabolism stalls where
  the animal is somewhat confined
• Attached to collection instruments for feces
  and/or urine
• Usually done in 2 phases
• Preliminary phase
• Frees digestive tract of any other types of feeds
• Animal gets accustomed to the process and feed
• 3-5d in pigs, 8-10d in ruminants

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Collection phase
• When feed and fecal collections are measured
• What are some of the chances for error in this
  system?
• Measures of Feedstuff Energy
• Total Digestible Nutrients (TDN)
• General, calculated amount
• Does not account for important losses of
  digestion
• Can be expressed as lbs., , or kg

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Can be extremely variable/inaccurate (usually
  overestimate)
• 1lb. TDN from 1.2 lbs. corn 1.2 Mcal NE
• 1lb. TDN from 2.1 lbs. hay 1.0 Mcal NE
• 1lb. TDN from 2.4 lbs. poor hay .8 Mcal NE
• Nutrient Partitioning in Digestion Metabolism
• Energy Units
• Calorie amount of heat needed to raise 1g water
  1ºC
• Kilocalorie 1000 calories
• Megacalorie 1000 kcal, or 1,000,000 calories
  (a.k.a. therm)

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Gross Energy (GE)
• Total potential energy of a feedstuff consumed
• Determined in a bomb calorimeter
• Fecal Energy (FE)
• Undigested residue that passes through the GI
• Can be collected and tested same method as above
• Digestible Energy (DE)
• DE GE FE
• Takes account of some losses during digestion
• Gasseous Products of Digestion (GPD)
• Combustible gasses that escape the body during
  digestion absorption
• Mostly methane some H, CO, acetone, etc.

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Most common in ruminants
• Hard to measure accurately
• Urinary Energy (UE)
• Includes materials that result directly from the
  digestion/absorption/enzymatic processes
• Many endogenous sources as well
• Metabolizable Energy (ME)
• ME DE UE GPD
• More accurate measure of nutritive value than DE
  and TDN
• Easy to determine in nonruminants because of the
  lack of GPD

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Heat Increment (HI)
• Increase in heat production following feed
  consumption
• Caused by the heats of fermentation, and heats of
  nutrient metabolism
• Energy is wasted unless the environmental
  temperature is below the animals critical
  temperature zone
• If it is used for temperature regulation, becomes
  part of NEm
• Net Energy (NE)
• NE ME HI
• Amount of energy used for maintenance only, or
  for maintenance and production purposes
• Function should be stated clearly when
  reporting/evaluating NE

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• NEm (NE for Maintenance)
• Part of total NE needed to keep animal in energy
  equilibrium
• No gain/loss of energy in body tissue
• Basal Metabolism energy needed to maintain
  basic vital cellular activity
• Energy of Voluntary Activity energy needed for
  basic movement to obtain food, water, lying down,
  etc.
• Heat to keep body warm additional heat needed
  when environmental temp lt animals critical
  temperature

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Heat to keep body cool extra energy expended
  when environmental temp gt animals thermo neutral
  zone
• NEp (NE Production)
• Additional energy required above NEm
• What would be considered production?
• NEl, NEg
• Energy in Beef Cattle
• This system can be used to accurately predict
  energy needs for wt. gain under normal conditions
• Make adjustments for abnormal conditions
• See tables 2-3, 2-4, and 2-5 for reference
• We will discuss further later in the semester

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Energy in Dairy Cattle
• NE values are much more accurate than any other
  system
• Evaluate NEm, NEg, and NEl
• NEl includes energy requirements for pregnancy,
  reproduction, and milk production
• NEl most often used component in ration
  formulation and evaluation
• Energy in Swine
• Generally use ME or DE as their evaluating tools
• Will eat to energy requirements if feed ad
  libitum
• Will cover further later

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Physical Evaluation of Feedstuffs
• Eye Appraisal
• Used mostly w/ forages
• Type
• Color
• of leaves
• Weed contamination
• Spoilage
• Palatability

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Factors Affecting Value
• Soil fertility
• Growing conditions
• Harvesting
• Stage of maturity
• Losses
• Processing Storage
• Evaluating Feeds Cost/Unit of Nutrient
• Cost of feed/unit wt. divided by unit wt.
  nutrient concentration
• Examples

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Unit 2 Evaluating Feedstuffs for Farm Livestock

• Unit 2 Assignment
• Review Problem Solving Questions
• 1-5
• Take your time!!!!