Lecture 2_Feed Analysis_Part 2_Fall20

Feed Analysis Overview

  • Lecture 2 - Part 2 covering various techniques of feed analysis, specifically focusing on fiber analysis methods, particularly the Van Soest method.

Van Soest Fiber Analysis

  • A systematic approach for assessing the fiber content in feed using different detergents to isolate cell contents and cell walls.

Cell Contents vs. Cell Wall

  • Cell Contents:

    • Digestible fraction of carbohydrates (CHO), proteins, lipids, and some minerals (ash).

    • Includes neutral detergent solubles (NDS) – substances that are easily digestible.

  • Cell Wall:

    • Composed of structural fiber and lignin, which are more difficult to digest.

    • Consists of neutral detergent fiber (NDF).

Generalized Plant Cell Structure

  • Cell Contents:

    • Includes sugars, starches, proteins, non-protein nitrogen (NPN), and lipids.

  • Cell Wall Composition:

    • Primary cell wall, secondary cell wall, and middle lamella containing:

      • Cellulose

      • Hemicellulose

      • Lignin

  • NDF and Digestibility:

    • As the age of plant material increases:

      • Cell wall toughness/thickness increases.

      • Lignin content increases, leading to higher NDF and decreased digestibility.

Van Soest Method Details

  • Digestive Process:

    • Forage is digested with neutral detergent to isolate cell contents (proteins, starch, sugars) and neutral detergent fiber (NDF) including hemicellulose, cellulose, and lignin.

    • Further digestion with acid detergent helps to isolate hemicellulose from cellulose and lignin (ADF).

    • Final digestion with 72% sulfuric acid separates cellulose from lignin.

Neutral Detergent Fiber (NDF)

  • Composed of cellulose, hemicellulose, and lignin.

  • Also includes silica and heat-damaged proteins.

Acid Detergent Fiber (ADF)

  • Defined as the product after boiling NDF in acid, which removes hemicellulose.

  • Contains cellulose and lignin, both of which are hard to digest.

Lignin Analysis

  • Analyzed by boiling ADF in strong acid, resulting primarily in lignin—considered indigestible and a structural filler in plants.

  • Lignin is not classified as a carbohydrate (CHO).

Plant Carbohydrates Overview

  • Summary categories:

    • Cell Contents: Organic sugars, starches, pectic substances.

    • Cell Wall: Cellulose, hemicelluloses, lignin.

    • Fiber categories: NDSF, NDSC, ADF, NDF.

Summary of the Van Soest Method

  • Fiber Classifications:

    • NDF: Cell wall components including cellulose, hemicellulose, lignin, and silicas.

    • NDS: Cell contents including lipids, sugars, starches, and proteins.

    • ADF: Cell wall components excluding hemicellulose (primarily lignin and cellulose).

    • ADL: Lignin portion of ADF.

  • Explains nutritional responses in terms of feed digestibility and consumption:

    • Higher NDF predicts lower voluntary feed intake.

    • Lower ADF indicates higher forage digestibility.

Non-Fiber Carbohydrates (NFC)

  • Calculated as NFC = 100 - (NDF + CP + CFat + Ash).

  • Comprises highly digestible carbohydrates such as sugars and starches.

Comparison of Fiber Analysis Methodologies

  • Proximate analysis vs. Van Soest method noted for distinct approaches to fiber analysis.

Additional Procedures in Analysis

  • Near Infrared Analysis (NIR):

    • Process involves drying and grinding samples, using near infrared light to quantify components through different absorption rates.

  • Challenges with NIR:

    • Requires calibration with wet chemistry, costly machinery, and not officially recognized for feed labeling.

Other Specialized Analysis Methods

  • Bomb Calorimetry: Measures energy.

  • Amino Acid Analysis: Via chromatography.

  • Atomic Absorption: Measures minerals.

  • Gas-Liquid Chromatography: Analyzes fatty acids.

  • Dumas Combustion Method: Measures non-metallic elements like nitrogen.

Biological Methods of Analysis

  • Methods Include:

    • In-situ digestibility trials.

    • Passage rate trials using markers.