Nutrient Analyses Study Notes

Nutrient Analyses

Introduction

  • Instructor: Dr. Jhones Sarturi

  • Course Information: Associate Professor, Department of Animal and Food Sciences, ANSC 3307 Feeds and Feeding, Lecture - 4

Learning Objectives of Lecture 4

  • Describe components of the Proximate Analysis

  • Recognize the fractions of detergent analysis of feeds

  • Discriminate calculation of Total Digestible Nutrients (TDN)

I. Proximate Analysis

A. Chemical Scheme of Feed Analysis

  • Historical Context: Developed in Germany in the 1860s to separate feed carbohydrates into digestible and less digestible fractions.

  • Components of Proximate Analysis:

    1. Dry Matter (DM)

    2. Ash

    3. Crude Protein

    4. Ether Extract

    5. Crude Fiber

    6. Nitrogen-Free Extract (NFE)

B. Dry Matter (DM)

  1. Definition: The percentage of dry matter is calculated as:
    DM ext{, } ext{%} = 100 - H_2O ext{, } ext{%}

  2. Determination: Typically determined by oven drying at 100°C to a constant weight.

    • Measurement of DM is crucial for:

      • Inventory control over feedstuffs, especially those with variable moisture content over time, such as high-moisture feeds.

      • Allows comparison of nutrient content on an equal basis.

  3. Limitations: Oven drying is not suitable for certain feeds, e.g., high-moisture fermented feeds, as it can lead to the loss of volatile compounds that are not water.

C. Ash

  1. Definition: Ash is determined by burning the sample at 500 to 600°C.

  2. Limitations: Provides limited nutritional information, as ash can be contaminated by non-nutritive components, such as soil and sand.

  3. Calculation: Organic matter as a percentage of dry matter is calculated as follows:
    extOrganicMatter=100−extash(drymatterbasis)ext{Organic Matter} = 100 - ext{ash (dry matter basis)}

D. Crude Protein (CP)

  1. Determination: Typically measured using the Kjeldahl procedure, which involves:

    • Digesting the sample in acid to convert nitrogen into salts.

    • Using alkali treatment and steam distillation to release the N salts as ammonia.

    • Titrating the ammonia concentration with a standard acid.

  2. Calculation: The percentage of crude protein is calculated as:
    extCrudeProtein=extPercentageofNimes6.25ext{Crude Protein} = ext{Percentage of N} imes 6.25

  3. Definition: Crude protein includes non-protein nitrogen present in the sample.

E. Ether Extract (EE)

  1. Definition: Ether extract is essentially crude fat and is measured by the weight of the feed sample that is extracted using ether, which includes:

    • Forage plants: primarily glycolipids.

    • Grains and oilseeds: consisting mainly of oils.

    • Animal products: composed of fats.

  2. Limitations: Ether extract may contain materials of limited nutritional value, e.g., wax.

F. Crude Fiber

  1. Testing Method: An ether-extracted sample is boiled in dilute acid, and then in dilute alkali.

  2. Components: It is a non-uniform feed fraction, including cellulose, hemicellulose, and lignin.

  3. Usage: It serves as a standard for feed labeling but has been replaced by detergent fiber analysis in research contexts.

G. Nitrogen-Free Extract (NFE)

  1. Calculation: Determined by difference as follows:
    extNFE=100−(extH2O+extCP+extEE+extash+extcrudefiber)ext{NFE} = 100 - ( ext{H2O} + ext{CP} + ext{EE} + ext{ash} + ext{crude fiber})

  2. Limitations: Errors in other procedures can lead to errors in NFE estimation.

    • Originally designed to represent the highly digestible carbohydrate fraction, but is not effective for this purpose due to variable fibrous fractions present.

II. Other Methods of Feed Analysis

A. Detergent Fiber Analyses

  1. Development: Established in the 1960s by Van Soest and colleagues to define fiber fractions in forages more effectively than crude fiber.

  2. Procedure:

    • Forage sample is boiled in neutral detergent solution to separate:

      • Neutral detergent solubles

      • Neutral detergent fiber (fiber fractions: cellulose, hemicellulose, lignin)

    • Followed by boiling in acid detergent solution to isolate:

      • Acid detergent fiber (comprising cellulose and lignin)

    • Further treatment with 72% H2SO4 is employed to determine acid detergent lignin from ash residue.

B. Analysis of Minerals

  1. Maximizing Mineral Extraction: Ash can be solubilized in acid to analyze specific minerals using various techniques:

    • Spectrophotometry (e.g., for phosphorus)

    • Atomic absorption/flame emission spectroscopy (e.g., for calcium and trace minerals)

    • Plasma emission spectroscopy (for most major and trace minerals)

C. Vitamins

  1. Methods of Analysis: Analyzed using spectrophotometric and/or chromatographic procedures.

III. Feed Energy Content

A. Gross Energy (GE)

  1. Definition: Gross energy offers no insight into the energy availability of feed. Must conduct digestion and balance trials to ascertain useful energy content.

  2. Caloric Content of Nutrients:

    • Carbohydrates: 4 kcal/g

    • Protein: 4 kcal/g

    • Lipids: 9 kcal/g

  3. Measurement Method: GE is determined when a sample is completely burned to its ultimate oxidation products, using a calorimetric bomb.

B. Total Digestible Nutrients (TDN)

  1. Purpose: TDN is a method for estimating the digestible energy of feeds.

  2. Calculation: TDN values are derived from combining lab analysis and digestibility data.

    • Calculation formula:
      TDN ext{, } ext{%} = ext{Digestible CP} + (2.25 imes ext{Digestible EE, } ext{%}) + ext{Digestible Crude Fiber} + ext{Digestible NFE}

    • Where:

      • Fat = 9 kcal/g

      • Proteins/Carbohydrates = 4 kcal/g

C. In Vitro Digestibility

  1. In Vitro Dry Matter Disappearance (IVDMD): Provides a relatively reliable estimate of forage digestibility and ranks digestibility among feeds.

  2. Calculation Formula:
    IVDMD ext{, } ext{%} = rac{ ext{dry sample weight - dry residue weight - blank}}{ ext{dry sample weight}} imes 100

  3. Blank Correction: The blank is represented by tubes without feed sample, thus correcting for any dry matter contributed by ruminal fluid.

D. Procedure for IVDMD

  1. Setup:

    • Centrifuge incubation followed by cooling in ice.

    • Collect ruminal fluid from a donor consuming a similar diet or evaluation feed.

    • Mixture ratio: sample + rumen fluid + artificial saliva added in a 4:1 ratio.

    • Incubate at 39°C for 24 to 48 hours before drying and weighing the residue.

IV. Near Infrared Reflectance Spectroscopy

  1. Useful Spectra: Provides spectra mainly for Hydrogen bonds, indicated as follows:

    • OH at 1600 e 2100 nm

    • H2O at 1450 e 1940 nm

    • CH at 1210, 1725 e 2310 nm

    • NH at 2055 e 2180 nm

  2. Calibration: Requires chemical analyses for calibration curves.