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AGR 4501 PASTURE MANAGEMENT 1
Nutritive Value of Pastures
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What is nutritive value?
The capacity of a feed to generate animal products if other factors are not limiting
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AnimalFeed Products (meat, milk)
geneticshealth
environment
wastes
quantity quality
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Good quality feed
Must be able to supply the nutrients required for growth and body functions of animal
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Nutrients
Energy Protein Minerals Vitamins Water
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Energy
The most important feed component if all other nutrients are adequate
Determines growth rate and productivity of animals
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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)
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Milk
Gross Energy
Net Energy
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Gross Energy (GE)
Digestible Energy (DE)
Metabolizable Energy (ME)
Net Energy (NE)
Faeces
Urine, methane
Heat
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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
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Measurements of Nutritive Quality
Digestibility Voluntary Intake Protein Content Mineral & Vitamin content
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Digestibility
Estimates the proportion of feed which can be digested (Intake-faeces)
Intake - faeces
intake
X 100 = % digestibility
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Factors affecting digestibility
Species Temperate > Tropical C3>C4
Age Digestibility declines with age
Temperature High temperature lowers digestibility
Protein Content If less than 7%
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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
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Cell wall
Cellulose Hemicellulose Lignin Silica
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As plants mature
Amount of cell wall increases Proportion of cell content decreases Percentage of indigestible components
increase Digestibility decreases
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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
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Methods of measuring digestibility
In vivo In vitro Nylon Bag Van Soest analysis
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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
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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)
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Rumen fistulated cattle
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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
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Rumen fistulated cattle
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Nylon bags filled with feed sample
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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)
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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
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Effects of protein on digestibility
% protein % digestibility
3.6 51.7
6.8 59.5
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Effects of protein on digestibility
% protein % digestibility
3.6 51.7
6.8 59.5
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Effects of minerals on digestibility
% sulfur % digestibility
0.09 55.2
0.15 60.2
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Measurements of Nutritive Quality
Digestibility Voluntary Intake Protein Content Mineral & Vitamin content
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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
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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
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Factors affecting V.I.
Digestibility Particle size of feed Protein content if <7 % Mineral content
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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
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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
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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
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Sward density effects on V.I.
Short, compact, grasses have higher intake – needs fewer bites compared to loose swards
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Methods of measuring intake
In vivo Indigestible markers for grazed pasture NDF is correlated with intake
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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
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Measurements of Nutritive Quality
Digestibility Voluntary Intake Protein Content Mineral & Vitamin content
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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
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Factors affecting protein content
Species: legumes 18-30% proteingrasses 6-15% protein
Age – protein declines as plant maturedecline is greater with
grasses
Nitrogen Fertiliser
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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
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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
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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
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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)
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Ether extract
Measures amount of fat Sample refluxed in ether to remove lipids
(fats)
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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
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Crude Protein
Measured by analysis of N using Kjeldahl Method.
%N x 6.25 = Crude Protein
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NFE
Calculated by
DM – Crude Fibre – Crude Protein - EE
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Weakness of Proximate Analysis
Don’t know what the analysis is actually measuring, especially, CF, EE and NFE
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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)
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Cell contents (soluble in neutral detergent) Lipids Sugars, organic
acids, water-soluble matter
Pectin Non-protein N Soluble protein
Almost completely digestible – not lignified
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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
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Basic Scheme of Forage Analysis Using Detergents
Fraction Reagent Treatment Yield
NDF
ADF
Lignin
Cellulose
Hemicellulose
Na lauryl sulphate, EDTA, pH 7.0
Cetyl trimethylammonium bromide in 1N H2SO4
72% H2SO4 treatment on ADF
None
None
Boil 1 h
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
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Sample
NDF:Cellulose, hemicellulose, lignin,
ADF: cellulose + lignin
hemicellulose
72% H2SO4
Lignin + minerals
550o C
Ash (minerals)
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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
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