2 Feed Eval I--Chemical analysis 2025

Evaluation of Feeds—Chemical Analysis

Purpose of Feed Evaluation

  • Provide rapid, economical, and accurate methods to evaluate feed quality

  • Measures of feed quality are not always definitive

  • Measures of feed quality vary according to:

    • Animal species (e.g., pig vs cow)

    • Physiological function of the animal (e.g., growth vs lactation)

Nutritional Value of Alfalfa

  • Importance of Feedstuff Evaluation:

    1. Diet formulation:

      • Improves prediction of animal performance

      • Enhances accuracy of ration formulations to meet targeted animal performance and feed utilization efficiency

    2. Economics:

      • Establishes accurate estimates of feed’s economic value

      • Nutrient variability of feeds: Forages > Grains > Protein meals

    3. Commerce: Texas Feed & Fertilizer Control Service

    4. Environmental impact:

      • Nutrient analysis of feeds required to comply with EPA regulations

      • Key nutrients of concern: nitrogen and phosphorus

      • More precisely formulated diets minimize nutrient excretion and adverse environmental impacts of animal feeding operations

Factors Affecting Nutrient Concentrations

  • Geographical location

  • Management practices (e.g., method of harvest, storage)

  • Soil fertility

  • Climate (e.g., drought, season)

  • Plant species

  • Stage of maturity of the plant

Nutritional Evaluation of Feedstuffs

  • Chemical analyses:

    • Proximate analysis system

    • Van Soest analysis system

    • Specific chemical analyses (e.g., minerals, vitamins)

  • Nondestructive analyses:

    • Near Infrared Reflectance (NIR) Spectroscopy

Animal-Based Methods (Research Only)

  • Metabolism trials

  • Feeding experiments

  • In vivo methods (Cannula: single or multiple)

Microbiological Methods (Available Commercially)

  • Nylon bag procedures (In situ)

  • In vitro procedures

Proximate Analysis System

  • Most common chemical-analysis method for quantifying nutritional value of feedstuffs

  • Designed to assess nutritional value without metabolism or feeding trials

  • Developed at Weende Experiment Station in Germany during the 1850s

  • Basis for Total Digestible Nutrient (TDN) system for evaluating energy availability

Breakdown of Proximate Analysis

  1. Water:

    • Heated at 105°C for 24 hours; calculated by weight difference

  2. Crude Protein (CP):

    • Kjeldahl method (older nitrogen analytical)

    • CP content = Nitrogen (N) content x 6.25 (inverse of 16% N in plant CP)

    • Leco Nitrogen method (newer nitrogen analytical method)

  3. Crude Fat (EE):

    • Dry sample extracted with petroleum ether; includes fats and less digestible pigments

  4. Ash:

    • Inorganic matter; combusted in a muffle furnace at 600°C for 24 hours

  5. Crude Fiber (CF):

    • Fat-extracted sample refluxed in weak acid and base; recovers cellulose, lignin, and hemicellulose

  6. Nitrogen-Free Extract (NFE):

    • Calculated (not actual chemical procedure); highly digestible CHO

    • Formula: NFE (DM basis) = 100 - (CP + EE + CF + Ash)

Weaknesses of Proximate Analysis

  • Separation inconsistencies in CHO components

  • Crude fiber assay doesn’t recover all fiber components

  • Considerable variability among feeds in fiber component recovery

Nutrients Found in Each Fraction

  • Ash: Macrominerals (e.g., calcium), microminerals (e.g., copper)

  • Crude Protein: Protein, amino acids, amines, non-protein nitrogen, nucleic acids, nitrates, and B-complex vitamins

  • Crude Fat: Fats, oils, waxes, organic acids, pigments, fat-soluble vitamins

  • Crude Fiber: Cellulose, hemicellulose, lignin

  • Nitrogen-Free Extract: Sugars, starch, pigments, fructans, pectins, some cellulose and hemicellulose

Van Soest Analysis System

  • Uses detergents to solubilize plant material; developed at Cornell University

  • Largely replaces crude fiber analysis in the industry

Components of Van Soest Fractions

  1. Neutral Detergent Fiber (NDF):

    • Total fiber CHO or cell wall content; correlated with feed intake

  2. Acid Detergent Fiber (ADF):

    • Consists of cellulose and lignin; correlated with digestibility

  3. Cell Contents (Non-Fiber Components):

    • Calculated as 100 - NDF (DM basis)

Fiber Carbohydrate Composition of Forages

  • Breakdown of cellulose, lignin, and hemicellulose percentages in various forages

  • Examples:

    • Alfalfa: Leaf (30% cellulose), Stem (17% hemicellulose)

    • Red Clover: Higher lignin levels in stems than leaves

    • Grasses: Varied percentages in Bromegrass and Orchardgrass

Chemical Analysis of Roughage, Grain, and High-Protein Feedstuffs

  • Comparative values obtained from proximate analysis and Van Soest analysis

Heat Damaged Forages

  • Excess heat from baling wet hay chemically alters protein quality (Maillard reactions)

  • ADF-CP used to measure heat-damaged protein; affects protein concentration adjustments

Chemical Analysis Technology—The Next Generation

Near-Infrared Spectroscopy (NIRS)

  • Used by large livestock producers for precision in diet formulation

  • Significant advantages include rapid analysis and simplicity of sample preparation

  • NIRS measures moisture, protein, fat, and fiber content with high precision

Characteristics of NIRS Analysis

  • Based on unique near-infrared absorption spectra for various chemical components

  • Requires statistical relationships for accuracy; calibration is key for results

Advantages of NIRS

  • Rapid analysis, no sample consumption, multiplicity of analyses, environmentally friendly

  • Limitations include high costs and less effectiveness for feeds without existing data

Conclusion

  • Diverse methods exist for evaluating feedstuffs for nutritional value and quality

  • Accurate feed analysis is crucial for optimizing animal performance and minimizing environmental impact.