Feed and Food Analyses - Animal Sciences 223

Animal Feeding and Nutritional Information Sources

• Requirements for Feeding an Animal: Proper animal nutrition is a multifaceted process that involves several critical considerations:   - Diet Formulation: The act of combining various feed ingredients to meet the specific requirements of the animal.   - Nutrient Utilization: Understanding how the animal processes and uses the nutrients provided.   - Nutrient Content of Ingredients: Identifying the specific nutritional profile of every individual ingredient in the ration.   - Quantity and Cost of Ingredients: Managing the availability and economic feasibility of the chosen feedstuffs.   - Physiological Requirements: Matching the diet to the specific status of the animal (e.g., growth, maintenance, lactation, or pregnancy).

• Sources for Nutrient Information:   - National Animal Nutrition Program (NANP): Accessible at http://animalnutrition.org.   - National Research Council (NRC): Reference guides that provide standard requirements for various species.   - USDA FoodData Central: Accessible at https://fdc.nal.usda.gov.   - Feedipedia: A European-based system found at http://www.feedipedia.org.   - Feed Tables: A European-based source accessible at https://www.feedtables.com/.

• Direct Analysis vs. Book Values:   - While reference guides provide "book values," these are ultimately not as accurate as the direct analysis of the specific ingredients and diets being fed to animals.   - Analytical Advancements: The speed and accuracy of nutritional technologies have significantly improved.   - Near-Infrared Spectroscopy (NIRS): An analyzer used to generate real-time data.   - Calibration Requirements: Even advanced NIRS machines must be calibrated using "wet chemistry" techniques, which remain the industry's gold standard for accuracy.

Introduction to Proximate Analysis

• Definition and History:   - Proximate analysis is a classical, sequenced approach used to analyze diets and feed ingredients.   - It was established at the Weende Agricultural Experiment Station in Germany in $1860$ by Henneberg and Stohman.   - It represents the earliest classification system for chemical components in diets.

• Nature of Measurement: It does not measure specific nutrients directly (such as individual vitamins, minerals, amino acids, or fatty acids); instead, it categorizes components into broad groups.

• Advantages of the System:   - Sequencing: The process is designed to move from one analysis to another without destroying the sample (with certain exceptions like CP).   - Efficiency: Requires relatively simple equipment and setup.   - Cost-Effective: Analyses are cheap and fast, allowing for the processing of hundreds of samples daily.   - Data Integration: Values obtained via proximate analysis are currently being correlated with rapid, non-destructive technologies like NIRS.

• Gravimetric Methods: Most proximate procedures are based on gravimetric methods, which involve the quantitative determination of an analyte based on the mass of a solid. Consequently, accurately and precisely weighing samples using an analytical balance is a critical laboratory skill.

The Six Components of Proximate Analysis

Partitioning a feed or ingredient into these six categories must total $100\%$ of the Dry Matter (DM):

1. Moisture

2. Crude Protein (CP): Calculated as $N \times 6.25$.

3. Ether Extract (EE): Also referred to as crude fat.

4. Ash: Represents the total mineral content.

5. Crude Fiber (CF)

6. Nitrogen-Free Extract (NFE)

Detailed Breakdown of Proximate Procedures

• Dry Matter (DM):   - Determined by "loss on drying" using two main methods:     - Direct Method: Direct extraction of water, often under vacuum. Note: this method also extracts volatile components.     - Indirect Method: Based on the low evaporation temperature of water; the sample is subjected to heat for a specific duration, and weight loss is assumed to be water.   - Standard Indirect Protocol: Dry samples at $105^{\circ}C$ for $12\text{-}16$ hours (overnight).   - Handling Wet Samples: Samples with high moisture must first be dried at $57^{\circ}C$ to avoid the loss of nutrients during the drying process.   - Laboratory Tools: Uses porcelain crucibles, foil cups, and vacuum desiccators. Note that samples can gain moisture weight if exposed to humid environments and may retain residual moisture even if they appear dry and powdery.

• Crude Protein (CP):   - Only the concentration of nitrogen ($N$) is measured.   - Kjeldahl Procedure: A classic method for organic $N$ involving digestion in hot sulfuric acid, followed by distillation and titration.   - Combustion Method: Measures total $N$ by heating samples to temperatures above $950^{\circ}C$ in pure $O_2$.   - Conversion Factor: Because proteins contain an average of $16\%$ nitrogen, the factor is derived as: $100\% \text{ total} \div 16\% \text{ N} = 6.25$.   - Formula: $\% N \times 6.25 = \% CP$.

• Ether Extract (EE):   - Measures crude fat. The sample is placed in a filter paper packet inside a Soxhlet apparatus.   - Diethyl ether is repeatedly refluxed through the sample, removing essentially all lipid components and depositing them in an originating flask.   - After the ether evaporates, the remaining lipid components are weighed.   - Safety Warning: This is a highly explosive technique.

• Ash:   - The sample is burned in a muffle furnace at $500\text{-}600^{\circ}C$ overnight.   - All organic compounds are removed via combustion.   - Significance: Ash represents the total inorganic mineral material. Individual minerals can be measured from the resulting ash residue.   - Organic Matter (OM) Calculation: $OM = DM - \text{ash}$.

• Crude Fiber (CF):   - The sample is boiled in an acidic solution, then an alkaline solution to loosely simulate digestion.   - The process generates a residue that is subsequently ashed.   - Calculation: Crude fiber is determined by subtracting the ash content from the residue.   - Composition: CF contains parts of cellulose, hemicellulose, and lignin.

• Nitrogen-Free Extract (NFE):   - Theoretically represents digestible carbohydrates (starch and sugars), but also includes oligosaccharides, pectin, and some hemicellulose.   - Formula (as-is basis): $NFE = 100 - (\text{moisture} + CP + EE + CF + \text{ash})$.   - It is a calculation by difference and can result in negative values for feedstuffs low in total carbohydrates.

Advanced Fiber Analysis: Van Soest Method

• The Van Soest method is significantly superior to Crude Fiber analysis, though Total Dietary Fiber (TDF) remains the ultimate gold standard.

• Methodology: Involves extraction and filtration into three components:   - Neutral Detergent Fiber (NDF): Represents the sum of hemicellulose, cellulose, and lignin.   - Acid Detergent Fiber (ADF): Represents cellulose and lignin.   - Acid Detergent Lignin (ADL): Represents pure lignin.

• Constituent Calculations:   - Hemicellulose: $NDF - ADF$.   - Cellulose: $ADF - ADL$.

Case Study: Practical Corn-Soybean Meal Diet for Swine or Poultry

• Initial Weights and Composition (As-Is Basis):   - Original Sample: $100\,g$.   - Moisture: $8\,g$ ($8.0\%$), resulting in a Dry Sample of $92\,g$ ($92.0\%$ DM).   - Ether Extract: $8\,g$ ($8.0\%$).   - Fat-Free Residue: $84\,g$.   - Crude Protein ($19.6\,g$ as-is) is determined via a separate destructive assay (no overlap with the residue sequence).   - Ash: $6.0\,g$ as-is ($4.0\,g$ residual ash measured from the insoluble portion).   - Crude Fiber: $7.0\,g$ as-is.

• Calculation of NFE (As-Is Basis):   - $NFE = 100 - (8.0 + 8.0 + 19.6 + 7.0 + 6.0) = 100 - 48.6 = 51.4\%$.

• Calculation of NFE (Dry Matter Basis - DMB):   - Method 1 (DMB Conversion): $51.4\% \div 0.92 = 55.9\%$.   - Method 2 (DMB Subtraction): $100 - (8.7\% EE + 21.3\% CP + 7.6\% CF + 6.5\% \text{ ash}) = 100 - 44.1 = 55.9\%$.

• Critical Observations:   - Since the original sample was $100\,g$, residual weights in grams equal percentages.   - The "solubilized portion" ($73\,g$ in this example) contains minerals available for absorption.   - Crude fiber is calculated as the difference between the "insoluble portion" and "residual ash."

Questions & Discussion

• What is the gold standard for fiber analysis?: Total Dietary Fiber (TDF) is considered the gold standard, though the Van Soest method (NDF/ADF) is a significant improvement over the original Crude Fiber (CF) measurement.

• Why dry wet samples at a lower temperature?: Samples are dried at $57^{\circ}C$ instead of $105^{\circ}C$ to prevent the loss of nutrients that might occur during rapid, high-heat drying.

• What course follows this one?: ANSC 322: Feeds and Feeding, taught by Dr. Josh McCann in the Fall (Tues/Thurs, $2:00\text{-}3:20\,PM$).