DIGESTIBILITY OF FEEDSTUFFS PP 96

1
DIGESTIBILITY OF FEEDSTUFFSPP 96 101
2
PURPOSES FOR DETERMINING FEEDSTUFF DIGESTIBILITY

• Evaluate and quantify available nutrients from
  individual feed ingredients
• Evaluate and quantify available nutrients from
  diets (complete food matrices)
• Quantify the available energy concentration of
  feedstuffs and or feeds
• Partition digestion of nutrients in different
  compartments of the digestive tract

3
DIGESTION TRIALSStandard Protocol

• Place animal in metabolism stall

4
Without Metabolism Stalls/Crates
5

• Adjustment Period
• First 10 to 14 days (can be shorter or longer
  depending on species, experimental design,
  discipline, etc)
• Free digestive tract of prior undigested feed
• Accustom animals to environment
• Feed to a constant rate
• Isocalorically (maintain body weight)
• Feed animal to attain 10 waste to determine ad
  libitum feed intake (typical for production
  animal trials)
• Do not collect feces or urine

6

• Collection Period
• Next 4 to 7 days
• Non ruminants 3 5 days
• Ruminants 5 7 days
• Carefully record feed intake
• Feed at 90 ad lib intake (if feeding ad lib)
• Collect all orts
• Must have accurate intake data
• Collect a diet sample subsample
• Collect all feces excreted, weigh
• Large animals - collect a 5 to 10 subsample
• Small animals (dogs, cats) 100 fecal sample
• (Optional) Collect urine, measure volume, collect
  a 5 to 10 subsample, and add to a composite
  urine sample

7
Important Measures

• Accurate feed intake
• Include weight of all orts
• Accurate fecal output
• (must know 100 weight even if you are
  subsampling)
• Appropriate diet samples
• Accurate urine volume (if included)

8
Post Collection

• Determine chemical composition and/or energy
  concentration of feed samples, feces, orts
• (Optional) Determine chemical composition and/or
  energy concentration of urine
• Calculate digestibility
• Digestibility () Consumed Excreted x 100
• Consumed

9
DIGESTIBILITY CALCULATIONS

• Dry matter intake (DMI)
• Average amount of feed x DM
• Fecal output (FO)
• Average amount of feces excreted x DM (feces)
• DM digestibility (DMD)
• (DMI FO)/DMI x 100
• Individual nutrient digestibility
• Example Protein
• (DMI x CPdiet FO x CPfeces)/(DMI x CPdiet )
  x 100

10
Application

• Concentration of the target digestible nutrient
  in diet (Example Protein)
• Crude Protein (DM) x Protein Digestibility
  Digestible protein, DM
• Can be done for each nutrient of interest

11
LIMITATIONS OF STANDARD DIGESTIBILITY TRIALS

• Apparent Digestibility (Apparent Digestion
  Coefficient)
• Feces composed of undigested nutrients and
  endogenous materials
• Endogenous materials
• Sloughed mucosa cells
• Bacteria
• Enzymes and bile salts
• How do you determine True Digestibility?
• Endogenous materials must be accounted for and
  removed from FO
• Accomplished by Ileal cannula (swine, dogs) or
  ceca removal poultry
• Used for amino acid digestibility in
  non-ruminants

12

• Limiting feed intake to 90 ad lib will slow rate
  of passage of digesta in the digestive tract
• Spillage and wastage of feed or feces
• Errors in analyses
• Sorting of feedstuffs

13
Production or Group HousingWhen animals cannot
be placed in metabolism stalls/crates
14

• Methods to determine digestibility in producing
  animals
• Fecal pans, bags
• Need to know individual feed intake
• Digestibility markers and indicators
• Characteristics
• Physiologically inert
• Contain no element under investigation
• Will not diffuse
• Totally indigestible
• Pass at uniform rate
• Readily determined chemically
• Examples
• Carmine
• Titanium oxide
• Acid Insoluble Ash (AIA)
• Chromic oxide

15

• Apparent Digestibility ()
• 100 indicator in feed x nutrient in
  feces x 100
• indicator in feces nutrient in
  feed

16

• Factors that Affect Digestibility
• Physiological stage of the animal
• Particle size/processing
• Disease state (parasites, antibiotic treatment,
  etc)
• Feed source and composition
• Level of intake
• Rate of passage
• Too slow high fermentation and putrefactive
  compounds
• Too fast incomplete digestion
• Nutrient imbalance (excess or deficiency)
• Matrices might be different than individual
  feedstuffs used

17
Balance Trials

• Account for losses associated with urine
• More precise measure of nutrient retention
• Commonly done for nitrogen to measure protein
  gain or loss
• Measurement
• Nitrogen balance
• (Nitrogen intake) (fecal nitrogen urine
  nitrogen)