Weende System: Proximate Analysis

• The Weende system, also known as proximate analysis, assesses the nutritional value of animal feeds.
• It was developed in the mid-19th century by Wilhelm Henneberg and Friedrich Stohmann at the Weende Experiment Station in Germany.
• The system separates feed components into six fractions.
  • Moisture
  • Crude protein
  • Ether extract (crude fat)
  • Crude fiber
  • Ash
  • Nitrogen-free extract (NFE)
• The Weende system is simple and inexpensive.
• It has limitations in accurately representing specific nutrient content and digestibility.

Proximate Analysis Fractions

• Moisture is determined by drying a sample in an oven until a constant weight is achieved.
  • The weight loss is considered moisture content.
• Crude Protein (CP) is estimated by measuring the nitrogen content of the feed and multiplying it by a factor, typically 6.25.
  • This calculation assumes that proteins contain 16% nitrogen.
• Ether Extract (EE), or crude fat, is determined by extracting a dried sample with ether.
  • The extracted material contains primarily fat, but may also include pigments, waxes, and other lipids.
• Crude Fiber (CF) represents the indigestible carbohydrate fraction.
  • Mainly cellulose, hemicellulose, and lignin.
  • Determined by sequential extraction with dilute acid and alkali.
• Ash is the inorganic residue remaining after burning a sample at high temperature (500-600°C).
  • Represents the total mineral content.
• Nitrogen-Free Extract (NFE) is calculated by subtracting the sum of CP, EE, CF, moisture, and ash from 100.
  • Supposed to represent the soluble carbohydrates like sugars and starches.

Determination of fractions

• To determine moisture, a feed sample is weighed and then dried in an oven, typically at 105°C, until a constant weight is achieved.
  • The difference in weight represents the moisture content.
• For crude protein, the Kjeldahl method is commonly used.
  • The sample is digested in sulfuric acid, converting nitrogen to ammonium sulfate.
  • Ammonia is then distilled off, collected, and quantified by titration.
• Ether extract uses diethyl ether in a Soxhlet apparatus to extract a dried feed sample.
  • The ether is evaporated, and the residue is weighed to determine the fat content.
• Crude fiber analysis involves boiling a dried, fat-extracted sample in dilute acid and then dilute alkali.
  • The remaining undissolved residue is dried, weighed, ashed, and the loss on ignition is the crude fiber.
• To determine ash, a feed sample is placed in a muffle furnace and heated to a high temperature (e.g., 600°C) until all organic matter is burned away, leaving only the inorganic ash.
• Nitrogen-free extract is not directly measured but calculated using the formula: NFE = 100 - (Moisture + CP + EE + CF + Ash).

Advantages

• The Weende system is relatively simple and inexpensive to perform.
  • Making it accessible for routine feed analysis.
• It provides a basic overview of the major nutrient fractions in feedstuffs.
• It has been used for a long time.
  • Providing a historical dataset for comparing feed compositions.
• It serves as a standard method in feed labeling regulations.
  • Ensuring a degree of consistency in nutritional information.

Disadvantages

• Ether Extract (EE) measures total lipids but does not differentiate between nutritional and non-nutritional lipids.
  • Resulting in an overestimation of the energy value.
• Crude Fiber (CF) does not accurately represent total dietary fiber.
  • Underestimates hemicellulose, pectin, and other soluble fibers, leading to an incomplete assessment of fiber's nutritional impact.
• The method for Crude Fiber (CF) can lead to inconsistent results.
  • Due to variations in the severity of the acid and alkali treatments.
• The calculation of Nitrogen-Free Extract (NFE) is prone to error.
  • Since it accumulates the errors from all other analyses, leading to inaccurate carbohydrate estimation.
• It does not provide information on specific amino acids, fatty acids, vitamins, or minerals.
  • Limiting its use in precise diet formulation.

Alternatives and advancements

• Van Soest Fiber Analysis is a more advanced method that separates fiber into neutral detergent fiber (NDF) and acid detergent fiber (ADF).
  • Providing a better estimate of total dietary fiber and its components.
• Near-Infrared Reflectance Spectroscopy (NIRS) uses infrared light to rapidly predict the chemical composition of feed samples.
  • Offering a faster and more cost-effective alternative to wet chemistry methods.
• Amino acid analysis by chromatography provides detailed quantification of individual amino acids.
  • Improving the precision of protein evaluation.
• Gas chromatography and mass spectrometry are used to determine the specific fatty acid profiles in feedstuffs.
  • Offering a more accurate assessment of fat quality.
• Inductively Coupled Plasma (ICP) Spectroscopy enables precise measurement of mineral content in feed samples.
  • Providing a comprehensive mineral profile.

Applications in animal nutrition

• The Weende system is used to formulate balanced diets for livestock.
  • Providing a basic understanding of the nutrient content in feedstuffs.
• It evaluates the nutritional quality of different feed ingredients.
  • Helping nutritionists select appropriate components for animal diets.
• The system ensures compliance with feed labeling regulations.
  • Providing consumers with information about the nutritional content of animal feeds.
• It monitors feed quality and consistency over time.
  • Identifying potential issues with nutrient content or ingredient composition.
• Proximate analysis helps predict the energy value of feedstuffs.
  • Which is essential for meeting the energy requirements of animals.

The Weende system, or proximate analysis, is used to assess animal feed's nutritional value. It separates components into six fractions: moisture, crude protein, ether extract, crude fiber, ash, and nitrogen-free extract. While simple, it has limitations in representing nutrient content and digestibility.