Energy in Animal Nutrition ANSC 223 Study Notes

Energy Overview

Learning Objectives for this Section

  - Understand energy partitioning in the body.
  - Explain the importance of basal metabolism.
  - Describe how energy is measured in the lab.
  - Explain how we measure energy production in animals using indirect calorimetry.
  - Conduct basic energy calculations.

What is Energy?

  - Definition: Energy is the capacity to do work.
  - Metabolism: This refers to the use of energy in the body, encompassing all chemical processes.
  - Usable Form of Energy: Adenosine triphosphate (ATP).

Nature of Energy

  - Not a Nutrient: Energy itself is not a nutrient but a property obtained from macronutrients.

Importance of Energy

  - Dietary Needs: Animals consume food/feed to meet specific energy requirements.
  - Example: Diet composition for a 3-week-old chicken:
    - Diet 1: 3,200 kcal ME/kg diet → Bird consumes 450 g feed → Energy consumed:
      $E_{consumed} = 3,200 ext{ kcal/kg} imes 0.450 ext{ kg} = 1,440 ext{ kcal}$
    - Diet 2: 2,400 kcal ME/kg diet → Bird consumes 600 g feed → Energy consumed:
      $E_{consumed} = 2,400 ext{ kcal/kg} imes 0.600 ext{ kg} = 1,440 ext{ kcal}$
    - Higher energy density leads to less diet consumed.

Energy and Food

  - Processes Involved:
    - Digestion → Metabolism (oxidation) → Chemical Energy (ATP).
    - Organic food nutrients contain locked-up chemical energy that is transferred through digestion and metabolism to become usable energy.
    - Stored Energy is utilized for Maintenance, Work, and Production.
    - Oxygen is critical for these processes.

Energy Interconversions

  - Energy can be stored and transferred between various forms.
  - Inefficiency: Each conversion incurs energy loss, primarily as heat.
  - Types of Energy Forms:
    - Dietary nutrients → High potential energy compounds (e.g., glucose, fatty acids).
    - Metabolic end products → Low potential energy compounds (e.g., CO2, H2O).
  - Productive Energy Applications:
    - Anabolism - tissue synthesis and repair.
    - Mechanical Work - muscle contraction.
    - Electrical Work - nerve transmission.
    - Osmotic Work and Concentration Gradients.

Energy Usage in the Body

  - Highest Priority: Basal Metabolic Rate (BMR).
    - BMR is the total energy expenditure while at rest in a neutral environment and post-absorptive state.
  - Energy for Body Functions (with examples):
    - Digested Energy → Body maintenance → Reproduction → Lactation → Storage (in muscle or adipose) → Body growth.

Basal Metabolic Rate

  - Energy Expenditure by Tissue:
    - Liver: 27%
    - Brain: 19%
    - Skeletal Muscle: 18%
    - Kidneys: 10%
    - Heart: 7%
    - Other Organs: 19%
  - BMR accounts for approximately 70% of daily energy expenditure in humans.

Energy Partitioning Process

  - Stages of Energy:
    - Gross Energy (GE)
    - Fecal energy loss (FE)
    - Digestible Energy (DE)
    - Urinary energy loss (UE)
    - Gaseous energy loss (GasE)
    - Metabolizable Energy (ME)
    - Heat Increment (HI)
    - Net Energy (NE) which can be divided further into:
      - NE maintenance
      - NE production (fetal growth, wool growth, lactation, weight gain).
  - Functionality:
    - $DE = GE - FE$
    - Total heat production includes both metabolizable energy and heat increment loss.

Heat of Combustion

  - Definition: Gross energy is defined as the heat released when a substance is completely burned to oxidation products (water, CO2).
  - Measurement Units::
    - A calorie is the amount of heat necessary to raise the temperature of 1 g of water by 1°C.
    - 1,000 calories = 1 kilocalorie (kcal) = 1 Calorie.
    - 1,000 kcal = 1 megacalorie (Mcal).
    - 1 kcal = 4.185 kJ.

Measuring Energy Content in Samples

  - Energy is measured by completely oxidizing a sample and measuring the heat released:
    - Materials Involved: Sample containing nutrients yields CO2 + H2O + gases and heat.
  - Methods: Using a bomb calorimeter, which operates at high pressure (25-30 atm) and can measure the energy content of organic samples.

Gross Energy Content Determinants

  - Determined largely by the Carbon:Oxygen ratio:
    - Example Compounds:
      - Glucose (C6H12O6): C/O = 1:1, 3.74 kcal/gram.
      - Alanine (C3H7NO2): C/O = 1.5:1, 4.35 kcal/gram.
      - Stearate (C18H36O2): C/O = 9:1, 9.53 kcal/gram.
  - General Values:
    - Gross energy per gram:
      - Carbohydrates: 4.1 kcal/g
      - Proteins: 5.7 kcal/g
      - Fats: 9.4 kcal/g.

Physiological Fuel Values (PFV)

  - Source of PFV Values:
    - Nutritional value derived from the product of gross energy and apparent digestibility minus urinary energy losses.
  - Example Values:
    - Carbohydrates: Gross Energy 4.15, Apparent Digestibility 97%, Urinary Energy Loss 0, Rounded kcal/g 4.03.
    - Fat: Gross Energy 9.50, Apparent Digestibility 95%, Urinary Energy Loss 0, Rounded kcal/g 9.02.
    - Protein: Gross Energy 5.65, Apparent Digestibility 92%, Urinary Energy Loss 1.25, Rounded kcal/g 3.95.

Components of Metabolizable Energy Measurement

  - Total Heat Produced Measurement Methods:
    - Direct Calorimetry: Direct measurement of heat.
    - Indirect Calorimetry: Based on biochemical principles with known combustion values of each nutrient.
    - Example Reactions:
      - $ext{Glucose} + O_2 <br>ightarrow CO_2 + H_2O$
      - $ext{Fat} + O_2 <br>ightarrow CO_2 + H_2O$
  - Key Measurements:
    - CO2 produced
    - O2 consumed
    - Respiratory Quotient (RQ) calculated as $rac{CO_2}{O_2}$.
    - For nitrogen-based measurements: Urinary N for protein oxidation used to factor energy calculations.

Indirect Calorimetry & Respiratory Quotient (RQ)

  - Measurement example using pure glucose:
    - $C_6H_{12}O_6 + 6O_2 <br>ightarrow 6CO_2 + 6H_2O + 672 ext{ kcal}$
    - Molar energy calculation:
      - Molar mass of glucose = 180 g/mol
      - Total energy from the oxidation of glucose = 672 kcal/mol glucose.
      - $6 ext{ mol } O_2 imes 22.4 ext{ L/mol } O_2 = 134 ext{ L } O_2 ext{ consumed/mol glucose oxidized}$
      - $rac{672 ext{ kcal/mol glucose}}{134 ext{ L O}_2} = 5.015 ext{ kcal/L } O_2 ext{ at STP}$
    - Measured RQ:
      - $rac{6 CO_2 ext{ produced}}{6 O_2 ext{ consumed}} = 1.0$
      - RQ of 1.0 indicates a thermal equivalent of 5.00 kcal/L.

Correction for Protein Oxidation

  - Adjustments for measurements considering protein contribute to calculations of RQ and O2 consumption:
    - Assuming standard values for protein metabolism:
      - Urinary N (g) x 6.25 = crude protein (g).
      - 1 g protein typically consumes 0.96 L O2 and produces 0.77 L CO2.
    - Corrected Measurements:
      - Adjust total CO2 produced by subtracting protein-related CO2 and O2 consumed.

Example Energy Calculations

  - Animal: Pig (Sus scrofa domestica) with a weight of 85 kg;
  - Body Weight (BW) to Metabolic Body Weight (MBW):
    - $ext{MBW} = ext{BW}^{0.75} = 28.0 ext{ kg}$.
  - Feed Intake: 1,892 g of diet (energy content 3.1 kcal/g).
  - Fecal Output: 1,232 g feces (energy content 1.8 kcal/g).
  - Urine Output: 2.7 L with 27 g of urinary N/L using 5.25 kcal/g.
  - Daily Energy Requirement & Expenditure Calculation:
    - Daily Energy Requirement:
      $ext{ME requirement} = 28.0 ext{ kg MBW} imes 70 ext{ kcal/kg MBW} = 1,960 ext{ kcal}$
    - Total Feed Energy Intake:
      $= 1,892 ext{ g of feed} imes 3.1 ext{ kcal/g} = 5,865 ext{ kcal} ext{ (GE intake)}$
    - Fecal Energy:
      $= 1.8 ext{ kcal/g} imes 1,232 ext{ g} = 2,218 ext{ kcal} ext{ (fecal energy)}$
    - Urinary Energy Calculation:
      - Urinary energy output is calculated as:
      $= 27 ext{ g N/L} imes 5.25 ext{ kcal/g N} imes 2.7 ext{ L} = 383 ext{ kcal}$
    - Digestible Energy (DE):
      - $DE = ext{Energy intake} - ext{Fecal energy (FE)} = 5,865 - 2,218 = 3,647 ext{ kcal}$
    - Metabolizable Energy (ME):
      - $ME = DE - ext{Urinary energy (UE)} = 3,647 - 383 = 3,264 ext{ kcal}$
    - Conclusion: The pig is in an active state of growth as the intake exceeds the needs.
    

Energy Calculations Summary

  - Macronutrient Values (as-is):
    - Crude Protein (CP): 21.5 % of diet, ME = 752.5 kcal/kg.
    - Nitrogen-Free Extract (NFE): 52.1 % of diet, ME = 1823.5 kcal/kg.
    - Crude Fat (EE): 11.2 % of diet, ME = 952.0 kcal/kg.
    - Total Energy: 3528.0 kcal from 1000 g of diet, approximately 27.0% of total energy.