DIGESTIBILITY OF FEEDSTUFFSPP 96 – 101

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

DIGESTION TRIALSStandard Protocol

• Place animal in metabolism stall

Without Metabolism Stalls/Crates

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

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

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)

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 100Consumed

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%

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

LIMITATIONS OF STANDARD DIGESTIBILITY TRIALS

1. 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

2. Limiting feed intake to 90% ad lib will slow rate of passage of digesta in the digestive tract

3. Spillage and wastage of feed or feces4. Errors in analyses5. Sorting of feedstuffs

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

– 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

Apparent Digestibility (%) = 100 – % indicator in feed x % nutrient in feces x 100

% indicator in feces % nutrient in feed

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

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)