Nutritional Value of Pasture

7/31/2019 Nutritional Value of Pasture

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Nutritional Value of Pasture

Substances Found in Living Things

Synthesis of Complex Organic Molecules & Breakdown of Complex

Organic Molecules to Simple Units

Simple Carbohydrate: Glucose, a monosaccharide or simple sugar


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The two forms of glucose as dissolved in water. They

interconvert. This hexose has six carbons.

Carbohydrates (C H O)

Carbon - grey

Oxygen - red

Hydrogen - white

A trios and two pentoses

Three different hexoses. Note carbon numbers.

Disaccharide formation by condensation, forming -1,4 linkage

Condensation to a disaccharide with -1,4 linkage


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Important Plant & Animal Polysaccharides

Hydrogen bonding to other cellulose occurs at OH by C 2

Glycogen & starch are -1,4 polymers with -1,6 branching

Cellulose is unique: alternate glucoses are flipped over and bonds

are beta 1,4 links

Polysaccharides

Starch is the major form of stored carbohydrates in plants. Starchis composed of a mixture of two substances: amylose, an

essentially linear polysaccharide, and amylopectin, a highly

branched polysaccharide. Both forms of starch are polymers of a-

D-Glucose.

How do animals digest the CHO made by plants?

Mammals produce enzymes that convert starch to disaccharides

and then to monosaccharides (break alpha 1,4 bonds).

Mammals don't make cellulase which breaks cellulose to

disaccharides, monosaccharides, etc. (need to break beta 1,4bonds).

How do animals use the cellulose from plant fibre?

They have bacteria in their intestines producing cellulase and other

enzymes which break plant fibre down.

The eventual products are Volatile Fatty Acids (Acetic A. 2C;

Propionic A. 3C; Butyric A 4C).

Structure of Lipids (fats and oils)


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The yellow pigment, beta-carotene is cleaved into two molecules of

Vitamin A.

This long chain and no polar groups makes it fat soluble.

Proteins are chains of amino acids. Not the NH2 amino groups.

20 different amino acids contribute to a wide variety of proteins.

Sulfur on amino acids cysteine and methionine creates bridges that


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give more specific structure to proteins.

Larger proteins have specific secondary, tertiary, and quaternary

structure.

Cellulose is only one part of plant cell wall fibre.

Hemicellulose has various 5C & 6C sugars and beta-1,4 linkages.

Lignin is an indigestible phenolic polymer that binds fibres.

Pectin forms gels and gives crispness.

Gums and mucilage contribute to gels and thickening of liquids.

Grazing Animals' Dilemma

Plants store much energy in bonds within fibre molecules.

Mammals do not produce enzymes to break these bonds

(beta-1,4, etc.)

Herbivorous mammals carry microbes in their stomach and

intestine which produce enzymes to digest someplant fibre

components.

Proximate Analysis of Feed Components


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Chemical Analysis Scheme

Digestibility of Nutrients

Digestion of organics is by hydrolysis, usually with enzymes

involved; not total.

Nitrogen in feed - Nitrogen in feces x 100

Nitrogen in feed

= Percentage Digestibility

Apparent Digestibility follows this formula and includes products

from the body.

True Digestibility is % of a nutrient actually absorbed from the GI

tract.

Energy Evaluation of Feeds (T 15.3 SFAP)

Contribution to energy digested: CHO > Fats > Proteins.

Total Digestible Nutrients (TDN) originated from: digestible crude

protein + digestible crude fiber + digestible nitrogen-free extract +

(digestible crude fat x 2.25).

TDN is used as crude measure of energy.


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Now TDN estimates are made from Acid Detergent Fibre (ADF)

content entered into specific formulas for each feed type.

Energy Measurements

A bomb calorimeter measures how much heat is released when a

sample is explosively burned

The result is gross energy.

How much energy can animals derive from feed?

Gross Energy

Corn, barley, and wood have similar GE.

Different animal species and feed types interact to determine what

% of GE is digested (DE) and what appears in faces.

DE minus E lost in urine + gases = Metabolizable Energy (ME)ME minus rumen fermentation - tissue metabolism - heat = Net

Energy

NEmaint; NEgrowth; NElactation

Energy Utilization by a Hen


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Laboratory Analysis of ForagesCrude protein (N x 6.25)

Ether extract (fat)

Fibre (NDF, ADF), Non-Struc CHO

Minerals (Ca, P, Mg, Mn, etc.)

Water

Vitamins

Above are all chemical analyses

Lab Analysis for EnergyThere is no direct analysis of one chemical which equals energy.

Energy comes from all the organic molecules to varying degrees.

Feed analysis labs measure two types of fibre. The lower these

fibre levels, the higher the available energy content.

Neutral Detergent Fibre (NDF)

Cell wall components: cellulose, hemicellulose, lignin, lignified N,

and insoluble ash (minerals).The lower the NDF, the more the animal will eat, thus inversely

related to consumption. It is an important component of dietary

fibre.

Acid Detergent Fibre (ADF)

Highly indigestible cellulose, lignin, and insoluble ash when an acid

detergent is used in processing.

Differs from crude fibre by including silica.

Silica and lignin cause low digestibility.


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Low ADF is desirable.

Slow chemical method and faster NIR.

Analysis

Chemical methods are slow and expensive.

Near infrared reflectance spectroscopy (NIRS) is non-destructive,

fast (< 3 min), accurate, and precise.

NIRS requires special instruments, complex data treatment, and

lack of sensitivity for minor components.

Typical Forage Analysis

Crude Protein

ADF

Energy estimate from ADF, usually Digestible Energy for horses

Ca, P

Non-Structural (Non-Fibre) CHO

Legumes, on average, have higher crude protein average than

grasses.


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Nutritional Value of Pasture