Feed Analysis Concepts

• Proximate analysis is a chemical method to determine animal feed composition.
• Henneberg and Stohmann developed the proximate analysis system in 1865 at the University of Gottingen's Weende Experimental Station in Germany.
• The system forms the basis of feed evaluation, quantitatively assessing food constituents, despite its age and limitations.
• The system analyzes six micronutrient categories: moisture (crude water), crude ash (CA), crude protein (CP), ether extracts (fats or lipids), crude fiber (CF), and nitrogen-free extract (NFE).

Water & Dry Matter (DM)

• Accurate dry matter (DM) determination in feeds is crucial for reliable measurement of other feed constituents.
• The water and dry matter content is determined by evaporating all moisture from the feedstuff.
• The weight of a representative feed sample is recorded before oven drying to remove moisture at 100-135°C.
• Drying methods approved by the Association of Official Analytic Chemists (AOAC) include drying at 100°C under vacuum of 1.3 x 10^4 Pa for 5 hours, in a forced-air oven at 135°C for 2 hours, or at 105°C for 6 hours.
• Labs use a two-step procedure for fermentable feeds with volatile compounds: determining a partial DM value by drying samples in a forced-air oven at 60°C overnight, followed by applying AOAC methods.
• Alternative moisture determination methods: toluene distillation, saponification, Karl Fischer method, gas chromatography, and Near-infrared reflectance spectroscopy (NIRS).

Crude Protein (CP)

• Crude Protein (CP) is determined using the Kjeldhal procedure, measuring total nitrogen content.
• The Kjeldahl procedure involves digestion, neutralization, and titration.
• The material is digested with sulphuric acid to convert all forms of nitrogen (except nitrates & nitrites) to ammonia, but ammonia gas is not liberated.
• Ammonia gas is liberated when the ammonium sulphate precipitate is neutralized with an alkaline such as sodium hydroxide (NaOH) then is combined with boric acid to convert to ammonium ions.
• Nitrogen concentration is estimated by titrating ammonium borate with sulphuric or hydrochloric acid.
• Hydrogen ion concentration at the titration end-point equals the nitrogen concentration in the original sample.
• Percentage CP is calculated by multiplying the nitrogen figure by 6.25, assuming proteins contain ~16% nitrogen.
• The CP value includes '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 the dry matter in a muffled oven at 550 to 600ºC to remove all organic matter.
• The leftover residue after burning represents inorganic constituents and total mineral content.
• Trace elements like selenium (Se), lead (Pb), and cadmium may volatilize during dry matter analysis of fermentable feeds' ashing process.
• Proximate ash analysis is often a preliminary step to specific mineral analysis using specialized equipment.

Crude Fibre (CF)

• Proximate analysis of crude fiber 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, rinsing, boiling in sodium hydroxide, and rinsing again.
• The residue is then dried, weighed, ashed, and re-weighed.
• Crude fiber content is the difference between pre-ash and post-ash weight.
• Peter Van Soest developed the detergent system of feed analysis at the USDA in the 1960s.
• Plant cells are divided into less digestible cell walls (hemicellulose, cellulose, lignin) and mostly digestible cell contents (starch and sugars).
• Two detergents used are a neutral detergent and an acid detergent.
• Neutral Detergent Fibre (NDF) is a good indicator of bulk and feed intake.
• Acid Detergent Fibre (ADF) indicates digestibility and energy intake.

Ether Extract (EE)/Crude Fat

• Ether extract/crude fat analysis measures lipids in feeds.
• Oven dried samples are ground and extracted with an organic solvent such as diethyl ether, and the remaining residue is dried and weighed.
• Ether extract is the difference between the original dried sample and the ether extract residue.

Nitrogen-Free Extract (NFE)

• Nitrogen-Free Extract represents a mixture of constituents not determined in the previous proximate analysis fractions.
• The NFE fraction mostly contains starches, sugars, pectins, and hemi-cellulose.
• NFE percentage is calculated by subtracting the sum of moisture, crude protein, crude fiber, ash, and ether extract (expressed as a percentage) from 100.

Proximate Analysis Limitations

• The analyses of ash, crude fibre (CF), crude protein (CP), and nitrogen-free extract (NFE) proximate constituents has limitations

Ash

• The remaining residual ash after ignition and burning of the dry matter sample is not truly reflective of inorganic material in food.
• Major drawbacks of ashing include loss of some inorganic material through volatilization, and presence of contaminants such as silica/carbon.
• The analysis is rendered less meaningful because it fails to provide quantitative information on specific minerals in feed.
• Alternative methods to correct this analytical deficiency include 'wet ashing' (used to analyze volatile trace minerals) and spectrophotometric analysis.

Crude Fibre (CF)/Nitrogen-Free Extract

• The error source in CF/EE analysis is the assumption that all substances soluble in organic solvents are lipids.
• Other extratts also contain fat-soluble vitamins, waxes, and pigments via solubilisation of plant cell-wall components.
• Inadequacies address using the detergent-based analytical system.
• V.J. Van Soest's detergent system divides feeds into a digestible fraction (sugars, starches, soluble protein, pectin, lipids) and a variable digestible fraction (insoluble protein, hemi-cellulose, cellulose, lignin, bound nitrogen).
• The final products are neutral detergent solubles (cell contents) and neutral detergent fibre (cell wall components).
• These two fractions are a more accurate representation of the carbohydrate constituent of feedstuff.

Crude Protein (CP)

• Crude protein analysis using the proximate analysis is a fairly good indicator.
• Crude protein analysis using the proximate system is based on the faulty premise that the average nitrogen content of crude protein in forages and feed is always 16%.
• Modern procedures such as the enhanced Dumas method (combustion elemental analysis) and UV-visible spectroscopy have vastly improved the efficiency and accuracy of measuring total nitrogen and protein in various feeds.

Detergent Method of Forage Analysis (Van Soest Method)

• The generally unsatisfactory nature of the Weende method for estimating the crude fiber content of foods and feeds has been recognized for many years.
• The Van Soest method of fiber analysis is widely used for determining the fiber content of plant materials, especially for animal nutrition studies.
• It was developed by Peter J. Van Soest and provides a more detailed breakdown of fiber components.
• The concept behind the detergent fiber analysis is that plant cells divided into less digestible cell walls (contains hemicellulose, cellulose and lignin) and mostly digestible cell contents (contains starch and sugars).
• Van Soest separated these two components successfully by use of two detergents: a neutral detergent (Na-lauryl sulfate, EDTA, pH =7.0) and an acid detergent (cetyl trimethyl ammonium bromide in 1 N H2SO4).
• Hemicellulose, cellulose and lignin are indigestible in non-ruminants, while Hemicellulose and Cellulose are partially digestible in ruminants.
• NDF = Hemicellulose + Cellulose + Lignin and ADF = Cellulose + Lignin.
• Neutral Detergent Fiber is a good indicator of "bulk" and thus feed intake, while Acid detergent fiber is a good indicator of digestibility and thus energy intake.

Principles of Energy Partitioning

• Energy is the capacity to do work in chemical, mechanical, and heat forms
• The energy in food is available to animals after it's broken down into nutrient components
• Energy absorbed by an animal is in nutrients like VFAs, amino acids, glucose, and lipids; not all energy in feed is available.
• The unit of energy is the joule (J); 4.184 joules = 1 calorie, 10^6 J = 1 megajoule (MJ).

Gross Energy (GE)

• Gross energy is the total energy in food. Some energy is excreted, lost as heat/gases.

Digestible Energy (DE)

• Digestible energy is the energy in food absorbed by an animal after digestion.
• DE represents the difference between energy in food and energy lost in faeces.

Metabolizable Energy (ME)

• Metabolizable energy is the energy remaining for the use of metabolic processes.
• Not all energy from digestion is available due to gas release, urine excretion, or heat loss during fermentation
• Loss of energy in urine and methane is approximately 19% of DE, thus constant relationship with DE content and DMD of the diet.
• ME can be calculated using the formula: ΜΕ = 0.81 DE
• ME values expressing energy content of feedstuffs are key to determining energy intake and formulating rations for ruminants.

Heat Increment (HI)

• The amount of energy needed to utilize circulating nutrients depends on what the nutrients are used for
• Heat is generated when ME coverts to NE
• The efficiency of converting ME to NE is given the symbol k and depends on diet ME content, and purpose for which NE is used

Net Energy (NE)

• Energy required at the tissue level for maintenance, growth, milk synthesis, etc.
• In the ME system, these energy requirements: NE values are converted to ME values using appropriate k values.
• Animals obtain NE for maintenance, lactation, or gestation by mobilizing stored energy (protein/fat).

Key concepts in feed sample analysis, including the Kjeldahl procedure for nitrogen determination. It also covers the Weende system for macronutrient categorization and crude ash analysis, emphasizing the importance of accurate dry matter determination and considerations in crude protein calculation.