RUMINANT DIGESTIVE TRACT

• Stomach– Reticulum, rumen & omasum

• Fermentation• Absorption of fermentation endproducts

– Abomasum• Secretion of hydrochloric acid and pepsinogen

• Small intestine– Similar to non-ruminant– No sucrase

• Large intestine– Similar to non-ruminant– More important in browsing species

CARBOHYDRATE DIGESTION IN RUMINANTS

Starch Structural CHO

Methane Undegraded Small intestine (Digestion similar to NR) Fermented

Volatile fatty acids (VFA)

Liver & peripheral tissues

Energy and fat synthesis

PROTEIN DIGESTION IN RUMINANTS

True protein NPN

Undegraded Small intestine Metabolizable Degraded proteinRecycled viasaliva (20% of dietary N) NH3 Microbial protein

NH3

Liver

Urea Kidney Excreted

LIPID DIGESTION IN RUMINANTS

Fat

Undegraded Small intestine (Digestion similar to NR) Degraded

Glycerol

VFA Long chain FA Saturated FA

Liver & peripheral tissues

Energy and fat synthesis

What is the primary volatile fatty acid produced in the rumen fed a high forage diet?

1. Acetic acid2. Butyric acid3. Lactic acid4. Conjugated linoleic acid5. Propionic acid

CHEMICAL ANALYSIS OF FEEDSTUFFSPages 87-93

FEED ANALYSIS SYSTEMS

• Needed to rationally group feed nutrients and requirements– Makes analysis relatively easy and cost-effective

• Feed analysis systems– Proximate analysis system (Weende system)

• Developed in 1864 at Weende Experiment Station in Germany

– Detergent analysis system (Van Soest system)

• Developed in 1964 at USDA Beltsville Research Center

PROXIMATE ANALYSIS COMPONENTS

• Dry matter (DM)• Ash• Crude protein (CP)• Ether extract (EE)• Crude fiber (CF)• Nitrogen-free extract (NFE)

FEED NUTRIENTS

Dry matter (DM)• DM,% = wt after drying/wt before drying x 100• % moisture = 100 – DM,%

• Example– Ending weight = 550 grams– Beginning weight = 750 grams– What is the % Dry Matter?– What is the % Moisture (water)?

73.3% Dry matter26.7% Moisture (water)

Problems with the DM method• Errors from losses of volatile components

– Major issue for fermented feeds• Toluene distillation or freeze drying

• Drying at 100o C destroys some nutrients and sample for further analysis– Freeze drying– Dry at lower temp for longer time for sample needing

further analysis (will still need to run DM on portion of sample)

Significance of Dry Matter– Considerable variation in the DM, % of feedstuffs

• Corn grain, 88% DM• Alfalfa hay, 90% DM• Alfalfa silage, 45% DM• Alfalfa pasture, 26% DM• Whey, 7%

– Other nutrients are present within the dry matter• Affects expression of concentrations of nutrients in feedstuffs• Example Crude protein, %

DM,% Wet basis DM basis– Dried distillers grains 93 27.9 30 – Modified distillers grains 50 15.0 30– Wet distillers grain 40 12.0 30

Significance of Dry Matter

DM,%

<30 30-60 60-75 68-75 >82

Putrefaction Ensiled forages

Mold & heating

High moisture grains

Dry grains and baled forages

• Affects storage properties of feedstuffs

FEED NUTRIENTS

Ash

Ash– Material remaining after oxidation of a sample

in a muffle furnace.• % Ash = wt after ashing/sample wt x 100%• % Organic matter = 100 - % ash

– Problems• No indication of amounts of individual minerals• Some minerals (Sulfur, Selenium, Zinc, Iodine are

lost)– Significance

• May indicate soil contamination or adulteration of feedstuff or diet.

What is in organic matter? a. Nitrogenous compoundsb. Proteinc. Fat soluble vitaminsd. Starche. All of the abovef. None of the above

FEED NUTRIENTS

Organic Matter

FEED NUTRIENTS

Crude Protein

Crude protein (CP)– Measures the nitrogen in a sample

• Kjeldahl N – acid base titration• N analyzer – combustion, measures nitrogen

– % Crude protein = %N x 6.25– What is % N?

• Most proteins contain 16% N; therefore every 100 mg of protein contains 16 mg nitrogen.

• 100 mg protein / 16 mg nitrogen = 6.25

CP,% = measured mg N/100 mg sample x 100 mg protein/16 mg N = measured mg N/100 mg/sample x 6.25

Question• Why have some foreign feed companies added

the compound to some feed ingredients?

A) Increase the energy concentration B) Increase the crude protein concentration C) Supply an essential amino acidD) Supply a required vitamin

• Problems with crude protein procedure – will not indicate protein quality, source of nitrogen, digestibility

• Sources of N: • True protein

– Chains of amino acids bound by peptide linkages– Can meet the protein requirements of either non-ruminant or

ruminant animals• Non-protein nitrogen

– Forms» Free amino acids» Nucleic acids» Ammonia» Urea » Biuret

• What form(s) of crude protein can be used to meet the crude protein requirement of a 120 lb growing gilt?

A. Chains of amino acids

B. Ammonia

C. Biuret

D. Urea

E. All of the above

• What form(s) of crude protein can be used to meet the crude protein requirement of a 800 lb growing steer?

A. Chains of amino acids

B. Ammonia

C. Biuret

D. Urea

E. All of the above

Crude protein says nothing about the digestibility of a protein

Example:

% Crude protein % Protein Digestibility

Soybean meal 45 90

Feather meal 80 75

Heat Damage of Proteins• When overheated (heat damaged)

– protein will bind to cell wall carbohydrates particularly across lysine– Reasons for this:

» Molding of forages» Over-heating during processing» Over-drying of grains or soybeans

– Referred to as the Maillard or Browning Reaction

– Results

% Crude protein % Protein Digestibility

Well-preserved alfalfa hay 18 90

Heat-damaged alfalfa hay 18 60

FEED NUTRIENTS

Ether Extract

Ether extract (EE)– Reflux ether through sample (solvent pulls lipid out)– % EE = (Sample wt-residue after reflux)/Sample wt) x 100%– Also called crude fat– Problem with procedure

• Ether extract consists of:– True lipids

» Fats and oils– Non-nutritional ether soluble components

» Fat-soluble vitamins» Chlorophyll» Pigments» Volatile oils» Waxes

FEED NUTRIENTS

Crude Fiber

Crude fiber (CF)• Extract with dilute acid, then dilute base, the residue

weighed then ashed. • % CF = (residue wt - Ash wt)/sample wt x 100%

– Theoretically represents: • the structural carbohydrates (Cellulose and hemicellulose)

– Limited digestibility in ruminants– Poor digestibility in non ruminants

• Lignin– Indigestible by ruminants and non ruminants

– Problems with procedure• Poor recovery of components

% recovered– Cellulose 90– Hemicellulose 50-60– Lignin 13-70 (very large error rate)

FEED NUTRIENTS

NFE

Nitrogen-free extract (NFE)– No actual analysis– Calculation by difference

• %NFE = %DM – (%ash+%CP+%EE+%CF)– Theoretically represents:

• Starch• Sugars

– Problems:• Contains all of the errors from other analyses

– Largest error is unrecovered lignin will be placed in NFE

WHY IS PROXIMATE ANALYSIS SYSTEM STILL USED?

DETERGENT ANALYSIS SYSTEM

Uses of the Van Soest system

• Predict intake (NDF)• Predict digestibility of forage (ADF)• Determine heat damage (ADF)• Determine Net Energy (NE) and Total

Digestible Nutrients (TDN) • Determine degradability of protein in rumen

• Neutral detergent fiber (NDF)– Consists of hemicellulose, cellulose, lignin, cell wall

bound protein and insoluble ash– Significance:

• Highly related to feed intake (index of “gut fill”)

• Acid detergent fiber (ADF)– Consists of cellulose, lignin, poorly digested protein,

and insoluble ash– Significance:

• Highly related to forage digestibility and energy concentration

– Combination of DDM (determined from ADF) and DMI (determined from NDF) is used to determine Relative Feed Value (RFV)

• Useful for hay marketing

Heat Damaged Forages• Typically occurs during ensiling when air gets

into the mass. – Result is aerobic rather than anaerobic fermentation– Increase in temperature– Protein and carbohydrate combine = unavailable

protein (Maillard reaction)– Determined by ADIN (Acid Detergent Insoluble

Nitrogen) – Analysis = ADF; Total N; N in the ADF fraction

General Guidelines on Heat Damage

• 0 – 10% Unavailable protein = little heat damage• 11 – 25% Unavailable protein = moderate to severe damage• > 26% Unavailable protein = Severe heat damage

• Example: Alfalfa silageTotal N = 3.05% ADIN = 0.25%3.05 – 0.25 = 2.80% N available2.80 / 3.05 x 100 = 91.8% nitrogen available or 8.2%

unavailable

N bound to NDF and ADF is used to determine rumen degradable, rumen undegradable, and indigestible fractions

Rumen degradable protein = Total CP – (NDFCP, % of CP x Total CP)

Rumen undegradable protein = (NDFCP, % of CP xTotal CP) –

(ADFCP, % of CP x Total CP)

Indigestible protein = (ADFCP, % of CP x Total CP)