Weende System of Feed Analysis

Weende System of Feed Analysis (Proximate Analysis)

• Proximate analysis is a chemical method for determining animal feed composition
• This System was created in 1865 by Henneberg and Stohmann at the Weende Experimental Station, University of Gottingen, Germany
• The system provides a quantitative way to assess food constituents and serves as the basis for feed evaluation
• The system analyzes six micronutrient categories based on biochemical properties:
  • Moisture (crude water)
  • Crude ash (CA)
  • Crude protein (CP)
  • Ether extracts (fats or lipids)
  • Crude fiber (CF)
  • Nitrogen-free extract (NFE)

Water & Dry Matter (DM)

• Determining dry matter (DM) content in feeds accurately is important for measuring the remaining feedstuff constituents
• Determining water and dry matter involves evaporating moisture from the feedstuff
• Initially, a representative sample is weighed and dried in an oven to remove moisture at 100-135ºC
• Association of Official Analytic Chemists (AOAC) approved oven-drying methods:
  • Drying at 100ºC under vacuum of 1.3 × 10^4 Pa for 5 hours
  • Drying samples in a forced-air oven at 135ºC for 2 hours
  • Drying at 105ºC for 6 hours
• A two-step procedure is used for fermentable feeds with volatile compounds when measuring DM and moisture
  • Determination of partial DM value by drying samples in a forced-air oven at 60ºC overnight
  • Applying AOAC methods to ground samples from the first step to get a total DM value
• Alternative moisture determination methods:
  • Toluene distillation (best for fermentable feeds)
  • Saponification
  • Karl Fischer method
  • Gas chromatography
  • Near-infrared reflectance spectroscopy (NIRS)

Crude Protein (CP)

• The Kjeldhal laboratory procedure measures total nitrogen content to determine crude protein (CP) in a sample
• The Total Nitrogen percentage is multiplied by 6.25 to give the approximate CP percentage
• The procedure includes digestion, neutralization, and titration
• Digestion with sulphuric acid converts all forms of nitrogen (except nitrates & nitrites) to ammonia
• Ammonium sulphate salt is formed, so ammonia gas is not liberated
• Neutralizing the ammonium sulphate precipitate occurs with an alkaline such as sodium hydroxide (NaOH) to liberate ammonia gas
• Boric acid combines with the ammonia to form ammonium ions (ammonium borate)
• Titrating ammonium borate with either sulphuric or hydrochloric acid estimates nitrogen concentration
• Hydrogen ions at the titration end-point equal the nitrogen concentration in the original sample
• Proteins contain approximately 16% nitrogen
• The CP value encompasses both 'true protein' and non-protein nitrogen (NPN) compounds like free amino acids, ammonium salts, and urea

Crude Ash

• Ash content is estimated by burning a pre-determined weight of dry matter at 550 to 600ºC in a muffled oven
• The residue represents inorganic constituents and total mineral content
• Selenium (Se), lead (Pb), and cadmium may be volatilized during the ashing of fermentable feeds
• Proximate ash analysis is a preliminary step to specific mineral analysis

Crude Fibre (CF)

• Proximate analysis of crude fibre estimates less soluble, fibrous fractions (lignin, cellulose, and hemi-cellulose) associated with feed carbohydrates
• The procedure involves boiling ether extract fat-free residue in acid solution, then boiling in sodium hydroxide
• The residue is then dried, weighed, ashed, and re-weighed
• Crude fibre content is the difference between the pre-ash and post-ash weight
• Peter Van Soest at the United States Department of Agriculture developed the detergent system of feed analysis in the 1960s
• The system is important in ruminant nutrition and increasingly, in non-ruminant research
• Plant cells are divided into less digestible cell walls (hemicellulose, cellulose, and lignin) and mostly digestible cell contents (starch and sugars)
• Two detergents separate these components:
  • Neutral detergent
  • Acid detergent
• Neutral Detergent Fibre (NDF) indicates bulk and feed intake
• Acid Detergent Fibre (ADF) indicates digestibility and energy intake

Ether Extract (EE)/Crude Fat

• Ether extract/crude fat analysis evaluates lipids in feeds
• Oven-dried samples are ground and extracted with an organic solvent like diethyl ether
• The ether extract is the difference between the original dried sample and the ether extract residue

Nitrogen-Free Extract (NFE)

• Nitrogen-Free Extract (NFE) represents a mixture of constituents not determined in the previous proximate analysis fractions
• The NFE fraction mostly contains starches, sugars, pectins, and hemi-cellulose
• Percentage of NFE = 100 - (Moisture + Crude protein + Crude fibre + Ash + Ether extract)

Proximate Analysis Limitations

• Proximate analysis has inherent limitations in analyzing fractions like ash, crude fiber (CF), crude protein (CP), and nitrogen-free extract (NFE)
• Improved procedures address these limitations

Ash Analysis

• Residual ash remaining after ignition of a dry matter sample does not truly reflects inorganic material in food
• Ashing drawbacks:
  • Loss of inorganic material through volatilization
  • Presence of contaminants (silica and carbon)
• Analysis fails to provide quantitative information on specific minerals in feed
• Alternative methods for correcting the deficiency:
  • wet ashing
  • Spectrophotometric analysis

Crude Fibre (CF)/Nitrogen-Free Extract Analysis

• Error in analysis of CF/EE occurs because it assumes all substances soluble in organic solvents such as diethyl ether are lipids
• Ether extracts also contain fat-soluble vitamins, waxes, and pigments from solubilization of plant cell-wall components
• The development and utilization of the detergent-based analytical system, devised by V.J. Van Soest, addresses these inadequacies:
  • High digestible fraction (plant cell contents): sugars, starches, soluble protein, pectin and lipids
  • Variable digestible fraction (plant cell wall contents): insoluble protein, hemi-cellulose, cellulose, lignin and bound nitrogen
• The final products are neutral detergent solubles (cell contents) and neutral detergent fibre (cell wall components)
• The detergent system independently or with the proximate analysis corrects the deficiencies of the CF/NFE system

Crude Protein (CP) Analysis

• Crude protein analysis using the proximate analysis is a fairly good indicator of test material protein content
• Protein analysis assumes that crude protein in forages and feed consistently has a 16% nitrogen content, which is a faulty premise
• The enhanced Dumas method (combustion elemental analysis) and UV-visible spectroscopy improve efficiency and accuracy of measuring total nitrogen and protein in various feeds

Detergent Method of Forage Analysis (Van Soest Method)

• The Weende method has unsatisfactory nature for estimating the crude fibre content of foods and feeds
• Boiling with dilute acid and with dilute alkali, which is taken to simulate gastric and intestinal digestion, frequently bears little relationship to the avail ability of complex carbohydrate determined by digestibility studies with animals
• The Van Soest method of fiber analysis is a widely used system for determining the fiber content of plant materials, especially for animal nutrition studies
• Peter J. Van Soest developed the method to provide a more detailed breakdown of fiber components
• The detergent fibre analysis divides plant cells into less digestible cell walls (hemicellulose, cellulose and lignin) and mostly digestible cell contents (starch and sugars)
• A neutral detergent (Na-lauryl sulfate, EDTA, pH =7.0) and an acid detergent (cetyl trimethyl ammonium bromide in 1 N H2SO4) successfully separated these two components
• Hemicellulose, cellulose and lignin are indigestible in non-ruminants
• Hemicellulose and cellulose are partially digestible in ruminants
• NDF = Hemicellulose + Cellulose + Lignin
• ADF = Cellulose + Lignin
• Neutral Detergent Fiber indicates "bulk" and feed intake
• Acid detergent fiber indicates digestibility and energy intake

Principles of Energy Partitioning

• Energy is the capacity to do work in forms including chemical, mechanical, and heat energy
• The energy contained in food is available to animals after the feed has been broken down into its nutrient components
• Nutrients (VFAs, amino acids, glucose, and lipids) are energy absorbed from feed by an animal
• Only some of the energy contained in feed is available to the animal
• The unit of energy is the joule (J) where 4.184 joules = 1 calorie or 10^6 J = 1 megajoule (MJ)

Feed Energy Partitioning

• Gross Energy (GE)
  • Gross energy is the total amount of energy in food
  • Some energy is excreted in urine and faeces, or lost as heat or gases from digestion
• Digestible Energy (DE)
  • Digestible energy (DE) refers to the amount of energy in a food source that is actually absorbed by an animal after digestion
  • DE represents the difference between the energy contained in the food and that lost in the faeces
  • Digestibility indicates feed quality, so the greater the digestibility, the more energy is available for metabolic activities (metabolizable energy)
  • Digestibility is expressed as a percentage of the feed dry matter (%DM)
• Metabolizable Energy (ME)
  • Not all digestion energy is available to animals, because some is released as gas, excreted in the urine, or lost as heat during rumen fermentation
  • Metabolizable energy is the energy remaining for the cow to use for metabolic processes
  • Approximately 19% of DE is lost in urine and methane
  • ME of a diet has a constant relationship with DE content and DMD of the diet
  • ME = 0.81 DE
  • ME values determine energy intake and formulate rations or supplements for ruminants
• Heat Increment (HI)
  • Heat generated by converting ME to net energy (NE) is debited against the ME content to calculate available energy for an animal
  • Energy losses can occur when:
    • Ingesting food from muscular activity in the jaws and the muscles of the gastro-intestinal tract
    • Microbial activity generates heat
    • Absorbing digested nutrients for chemical reactions
  • Utilising circulating nutrients depends on their purpose, e.g. Metabolizing glucose for ATP requires less energy than synthesizing fat
  • HI is referred to as the specific dynamic action of food
  • The efficiency of converting ME to NE is given the symbol k where K = NE/ME
  • ME to NE efficiency varies:
    • Depending on the ME content of the diet
    • Depending on the purpose for which the NE is used
• Net Energy (NE)
  • Net energy refers to the energy required at the tissue level for maintenance, growth, milk synthesis, etc
  • ME system expresses energy requirements in units of ME by converting NE values using appropriate k values
  • Animals obtain NE for maintenance, lactation, or gestation by mobilizing stored net energy in the body in the form of protein and fat