AGR 4501 PASTURE MANAGEMENT1 Nutritive Value of Pastures

AGR 4501 PASTURE MANAGEMENT 1

Nutritive Value of Pastures

What is nutritive value?

The capacity of a feed to generate animal products if other factors are not limiting

AnimalFeed Products (meat, milk)

geneticshealth

environment

wastes

quantity quality

Good quality feed

Must be able to supply the nutrients required for growth and body functions of animal

Nutrients

Energy Protein Minerals Vitamins Water

Energy

The most important feed component if all other nutrients are adequate

Determines growth rate and productivity of animals

Energy in feed

Total energy in feed = Gross Energy (GE) units : MJ (mega joules) per kg

Energy which can be used for growth = net energy (NE)

Gross Energy

Net Energy

Gross Energy (GE)

Digestible Energy (DE)

Metabolizable Energy (ME)

Net Energy (NE)

Faeces

Urine, methane

Types of feed and energy content

Concentrates e.g. corn, wheat – high energy feed >10 MJ/kg

Forages and Roughages including pasture: high fibre <10 MJ/kg

Measurements of Nutritive Quality

Digestibility Voluntary Intake Protein Content Mineral & Vitamin content

Digestibility

Estimates the proportion of feed which can be digested (Intake-faeces)

Intake - faeces

intake

X 100 = % digestibility

Factors affecting digestibility

Species Temperate > Tropical C3>C4

Age Digestibility declines with age

Temperature High temperature lowers digestibility

Protein Content If less than 7%

Effects of cell structure on digestibility

Plant cells are comprised of: Cell contents Cell wall

Cell contents Comprise of soluble carbohydrate, protein,

completely digestible Cell wall

Partially digestible

Cell wall

Cellulose Hemicellulose Lignin Silica

As plants mature

Amount of cell wall increases Proportion of cell content decreases Percentage of indigestible components

increase Digestibility decreases

At the plant level

Proportion of stems increases with age Stems become harder (more lignin) as

plant age Proportion of old and senescing leves

increase

Methods of measuring digestibility

In vivo In vitro Nylon Bag Van Soest analysis

In vivo

Use real life animal Weigh feed and offer to animal Weigh uneaten feed the next day Calculate feed intake (feed offered-feed

remaining) Weigh faeces Calculate digestibility 7 days adaptation 10 days measurement

In vitro

(Tilley & Terry, 1963) Obtain rumen fluid from fistulated animal Provide anaerobic condition by infusing

nitrogen Incubate ground dried feed sample 39oC

for 48 hrs Add acid pepsin and incubate in aerobic

condition for 48 hrs Filter and weigh residue (undigested)

Rumen fistulated cattle

Nylon Bag

Use 6 g of dried ground sample Wrap in nylon bags 15x6 cm Introduce into rumen via fistula Leave for 48 hr Remove bags and incubate further in

acid pepsin for 48 hr Weigh residue

Rumen fistulated cattle

Nylon bags filled with feed sample

KN4, 6 and 8 WAP AH and SBM

Sampled and dried groundCP, OM, NDF and ADF

determination

In situ DM and CP disappearanceusing nylon bag technique

Insertion of nylon bags into the rumenfor 72, 48, 24, 16, 12, 8 and 4h

Removed,washed

Ruminal degradation study (Nylon bag technique)

Intestinal digestion study (mobile bag technique)

Test samples were incubated in the rumen for 16 and 24h

Removed, washed and dried

Each dried residual sample was fitted (0.5g) into six mobile bags and sealed

Incubated in a Pepsin-HCL solution for 1hat 37 ºC, rinsed and then kept on ice, 4 ºC

Introduced into duodenum

of canulated steers, 20 min./bag

Collected from the feces,

stored at -18ºC, washed

DM, CP, amino acid* determinationCalculation of intestinal DM, CP and

amino acid* disappearances * Ruminal and intestinal residues will be analyzed for amino acids later

Effects of protein on digestibility

% protein % digestibility

3.6 51.7

6.8 59.5

Effects of protein on digestibility

% protein % digestibility

3.6 51.7

6.8 59.5

Effects of minerals on digestibility

% sulfur % digestibility

0.09 55.2

0.15 60.2

Voluntary Intake

The quantity of feed ingested by animals when fed ad libitum

Influenced by animal size, breed, physiology and health

Higher quality feed should have higher intake

Voluntary Intake

Unit of measure g/kg liveweight0.75

eg. Weight of cow 150 kg, consumes 3 kg DM, V.I. = 3000/1500.75 = 3000/42.86 = 70 g/kg0.75

Factors affecting V.I.

Digestibility Particle size of feed Protein content if <7 % Mineral content

Mechanism controlling intake

Intake depends on rate of passage through rumen and alimentary tract

Fast rate of passage, more feed can be ingested

Feed of low digestibility and low protein stays longer in rumen

V.I. can be improved by

Grinding or chopping feed to smaller particles

Adding protein or urea to low protein feed

Adding minerals which are deficient

Leaf:stem ratio affects V.I.

Kabulabula Hamil

% leaf 28.0 53.0

% digestibility 55.2 55.5

V.I. g/kg0.75 49.1 67.3

Sward density effects on V.I.

Short, compact, grasses have higher intake – needs fewer bites compared to loose swards

Methods of measuring intake

In vivo Indigestible markers for grazed pasture NDF is correlated with intake

Indigestible marker

Chromium oxide Dose animal with known amount of

marker Analyse the faeces for the marker Estimate the amount of faeces Knowing digestibility of feed, can

calculate intake

Protein content

Protein required by animals for growth, milk production and reproduction

Protein requirements vary between stage of growth of animals, dry and lactating

Critical level is at 7% protein, below which feed intake is reduced

Factors affecting protein content

Species: legumes 18-30% proteingrasses 6-15% protein

Age – protein declines as plant maturedecline is greater with

grasses

Nitrogen Fertiliser

Measurement of Protein

Protein contains ~ 16% N

To determine protein content, analyse N content and multiply by 6.25 (100/16=6.25) eg. 2% N = 12.5% protein

Measurement of N by Kjeldahl method

Mineral content

Lack of minerals will results in metabolic disorder

Supply mineral lick or supplements to overcome deficiency

Plants usually have low P and Na compared to animal needs

Indirect Measurement of Nutritive Value

Based on fibre content and composition Can be correlated with digestibility and

intake The method is faster and less expensive

Proximate Analysis

Has been in use for more than 150 years Sample is analysed for the following

components: Dry matter Ether Extract Crude Fibre Crude Protein Nitrogen-free extract (NFE)

Ether extract

Measures amount of fat Sample refluxed in ether to remove lipids

(fats)

Crude fibre

Fat-extracted residue refluxed in 1.25% sulfuric acid for 30 mins

Followed by reflux in 1.25% sodium hydroxide for 30 mins

Crude Protein

Measured by analysis of N using Kjeldahl Method.

%N x 6.25 = Crude Protein

Calculated by

DM – Crude Fibre – Crude Protein - EE

Weakness of Proximate Analysis

Don’t know what the analysis is actually measuring, especially, CF, EE and NFE

Van Soest Detergent System

To replace the Crude Fibre component Plant sample divided into the following

components: Cell Wall (Neutral Detergent Fibre NDF) Cellulose + lignin + (others, pectin, tannin,

silica) (ADF) Hemicellulose = NDF – ADF Lignin Ash (minerals)

Cell contents (soluble in neutral detergent) Lipids Sugars, organic

acids, water-soluble matter

Pectin Non-protein N Soluble protein

Almost completely digestible – not lignified

Cell wall constituents (fibre insoluble in neutral detergent)

Soluble in acid detergent (NDF) Hemicellulose Fibre bound protein

Acid detergent fibre (ADF) Cellulose Lignin Lignified N

Basic Scheme of Forage Analysis Using Detergents

Fraction Reagent Treatment Yield

Lignin

Cellulose

Hemicellulose

Na lauryl sulphate, EDTA, pH 7.0

Cetyl trimethylammonium bromide in 1N H2SO4

72% H2SO4 treatment on ADF

Boil 1 h

3 h, 20o C

Ash residue from lignin step

NDF-ADF

Plant cell wall less pectins

Lignocellulose + insoluble minerals

Crude lignin

Loss in weight

Sample

NDF:Cellulose, hemicellulose, lignin,

ADF: cellulose + lignin

hemicellulose

72% H2SO4

Lignin + minerals

550o C

Ash (minerals)

Correlations of various forage components with in vivo voluntary intake and digestibility

of 187 forage species

Component Digestibility Intake

Digestibility in vivoDigestibility in vitroLigninADFNDFCPCelluloseHemicellulose

-+0.80-0.61-0.75-0.45+0.44-0.56-0.12

+0.61+0.47-0.08-0.61-0.76+0.56-0.75-0.58

AGR 4501 PASTURE MANAGEMENT1 Nutritive Value of Pastures

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