Bioenergetics

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Bioenergetics
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Homeostasis

• Definition
• The state of sustained equilibrium in which all
  cells, and all life forms, exist
• Integration of all pathways
• In different metabolic situations
• Utilization of nutrients

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Bioenergetics

• The study of energy supply, utilization and
  dissipation
• Energy is the capacity for performing work
• Nutrients contain chemical energy which is
  yielded upon metabolism
• Used for chemical, mechanical, electrical or
  osmotic work

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Functions of Energy

• Energy ability to perform work
• Mechanical work
• Formation of substrates
• Active transport
• Transfer of genetic information
• Maintenance

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Pathways of Metabolism
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Why does fat have so many calories?

• C-H bonds release more energy when broken than do
  C-O bonds.
• Fats contain more C-H bonds and carbohydrates and
  proteins contain more C-O bonds.
• Thus, fats contain more potential energy than
  do the others.

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Pathways of Metabolism
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Energy

• Released energy is trapped in high energy
  phosphate bonds

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Energy Units

• Joule
• Joule kg/(m2?s2)
• Older unit still used in the US is calorie (cal)
• 1 calorie heat required to increase the
  temperature of one gram of water from 14.5 to
  15.5C
• 1 calorie 4.184 J
• More frequently used measurements
• 1000 calories 1 kcal
• 1000 kcal 1 Mcal

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Efficiency

• Efficiency of conversion of chemical to work
  energy is less than 25
• Remainder is converted to thermal energy (i.e.,
  heat)

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Efficiency of Converting Feed
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Energy Value of Selected Feeds
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Formation and Use of Energy
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Overview of Energy Metabolism
Productive Functions
Feed
Heat
Water Protein Fat CHO
Mineral Vitamin
Maintenance Growth Work Lactation
Gestation
Nutrients to Tissues
Feces
Gas
Urine
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The Basics

• The Energy Balance Equation
• Energy In Energy Out Energy to Stores
• Remember that energy can be neither created nor
  destroyed
• If you eat it, it has to either be used or stored
  or excreted
• This is not rocket science

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Energy Balance

• Positive energy balance
• Energy in gt energy out
• Weight gain
• Negative energy balance
• Energy out gt energy in
• Weight loss
• Energy equilibrium
• Energy out energy in
• Weight maintenance

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What makes up energy in?

• Simply, the amount of energy ingested in
  feedstuffs
• 4 kcal/g carbohydrate
• 4 kcal/g protein
• 9 kcal/g fat
• 7 kcal/g alcohol

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Feed
Heat
Water Protein Fat CHO
Mineral Vitamin
Nutrients to Tissues
Feces
Gas
Urine
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Need to Get a Useful Energy Value

• Fecal loss is significant in all animals
• Total Digestible Nutrient (TDN) system attempted
  to improve energy value by adjusting for
  digestibility
• TDN does not account for other potential losses -
  particularly those associated with fermentation

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Total Digestible Nutrients (TDN)

• Determined by a digestion trial
• Calculate the sum of nutrient digestibility
• Values lie between DE and ME
• 1 kg TDN 4.4 Mcal DE
• Similar disadvantages as DE

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Total Digestible Nutrients
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Net Energy System

• Improved on TDN system
• Direct application of the First Law of
  Thermodynamics
• Energy can be neither created or destroyed
• Energy can be interconverted between different
  forms
• Thermal energy cannot be converted to any other
  form

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Energy Partitioning
Gross Energy (GE)
Energy Lost
In feces (FE)
Digestible Energy (DE)
In urine and gases (UE and GPD)
Energy Lost
Metabolizable Energy (ME)
Energy Lost
In heat (HI)
Net Energy (NE)
NEm
NEg
NEl
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Gross Energy (GE)

• Represents total energy content of feed
• Heat of combustion
• Bomb calorimeter
• Energy released as heat when a feed if completely
  oxidized to CO2 and H2O
• Provides little information on nutrient
  utilization

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Net Energy System
Gross Energy (GE)
Digestible energy (DE)
Fecal energy Undigested feed residues
Metabolic products Mucosa Bacteria
Enzymes
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Digestible Energy (DE)

• DE GE fecal energy
• Apparent digestibility
• Provides some assessment value
• Similar to TDN
• Major weakness
• Overestimates value of high fiber diets

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Fecal Energy (FE)

• Largest energy loss
• Two sources
• Undigested food
• Indigestible
• Increased rate of passage
• Endogenous
• Active secretion
• Cells slough
• Undigested microbes and their metabolites

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Digestible Energy (DE)

• Losses for ruminants (cattle and sheep)
• 40-50 for roughages
• 20-30 for grains
• Losses for horses are 35-40
• Used by horse NRC
• Losses for pigs are 20

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Energy Value of Selected Feeds
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Net Energy System
Digestible Energy (DE)
Metabolizable energy (ME)
Urinary energy N disposal and Gaseous
energy Gaseous products of fermentation
(CH4) - lost via belching or bowels
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Metabolizable Energy (ME)

• ME DE gas and urine (UE) energy
• Greater assessment value than DE
• Used by swine and poultry NRC
• Used in human nutrition
• Can be calculated from DE (rather than directly
  measured)

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Urinary Energy (UE)

• Total gross energy in urine
• Includes energy from
• Nonutilized and absorbed compounds from food
• End products of metabolism
• End products of endogenous origin
• Loss is relatively stable
• Influenced by diet
• Excess protein
• Urea in mammals
• Uric acid in birds
• 2-3 of gross energy for pigs
• 4-5 of gross energy for cattle

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Gaseous Energy

• Methane (CH4) is main form lost as gas
• Hydrogen, CO2, acetone, ethane and hydrogen
  sulfide
• Greatest gaseous losses in ruminants
• 82 of DE
• Gaseous losses so small that not considered for
  ME calculation in man, pigs, dogs and chickens
• gt95 of DE
• H, CO2, acetone, ethane
• Can be measured directly or indirectly

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Energy Value of Selected Feeds
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Net Energy System
Metabolizable Energy (ME)
Net energy (NE)
Heat increment energy Heat of digestive
fermentations and actions Heat of
metabolism
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Net Energy (NE)

• NE ME heat increment (HI)
• NEm, NEg, Nel
• Maintenance, gain and lactation
• Best indication of energy available for
  maintenance and production
• Used by beef, dairy and sheep NRC

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Heat Increment (HI)

• Losses of energy as heat
• Basal metabolism
• Muscular activity
• Digestion and absorption
• Microbial fermentation
• Product formation
• Waste formation and excretion
• Thermal regulation

• Can represent 25-40 of gross energy intake
• 2nd largest energy loss
• Lowest HI for fat
• Highest HI for fiber

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Net Energy (NE)

• End products of digestion are used at different
  levels of efficiency for various functions
• Not possible to assign a single NE value to a
  feedstuff
• Corn grain (Mcal/kg) 2.16 NEm 1.48 NEg 2.05
  NEl

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Energy Value of Selected Feeds
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Net Energy System
Production (NEg or NEl) Tissue growth
Stored in products Work
Net Energy (NE)
Maintenance (NEm) Basal metabolism
Activity at maintenance Sustaining body
temperature
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NEm

• Quantity of energy an animal would use to form
  tissue, fat and protein to stay alive
• Quantity of feed necessary to prevent tissue loss
  from an animals body

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Maintenance

• The amount of energy (or protein) needed to
  maintain an animal in zero energy (or protein)
  balance
• Strictly speaking, only applies to a mature,
  non-pregnant, non-lactating animal
• But in practice the concept is widely applied to
  productive animals

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Efficiency

• Maintenance feed requirements have a major effect
  on efficiency of feed utilization
• gt40 energy intake is used to support maintenance

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Total Net Energy
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79
40
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Maintenance Energy Components
Maintenance Energy Requirement
Basal Metabolism
Muscular Work
Temperature Regulation
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Basal Metabolism

• Metabolic rate in postabsorptive state, with
  minimal activity, thermal and psychic stress,
  needed to sustain life
• Basal metabolic rate (BMR)
• Maintains cellular activity, respiration, and
  blood circulation
• Affected by
• Body size
• Species
• Age
• Previous level of nutrition
• Climate

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Contribution of Specific OrgansMature Sheep
Maintenance Costs
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Body Size

• The bigger an animal, the more heat it produces
• Relationship is curvilinear

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Body Size

• Plotted on logarithmic scale
• Relationship becomes linear

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Metabolic Body Size

• W0.75
• Used to compare mature animals of different body
  size
• Used to determine maintenance energy requirements
• Heat dissipation correlated to body surface area
• Used to compare metabolism of different species

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Metabolic Body Size
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Age

• Basal heat production, corrected for metabolic
  body weight, declines quickly from birth to
  weaning, then more slowly to maturity

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Climate

• Prolonged cold causes increased basal heat
  production
• Prolonged heat caused decreased basal heat
  production

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Maintenance Energy Components
Maintenance Energy Requirement
Basal Metabolism
Muscular Work
Temperature Regulation
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Muscular Work

• Effects of exercise on maintenance requirements
  depend on
• Work intensity
• Work duration
• NRC (National Research Council animal feed
  requirements) tables usually add a correction
  factor of 10 of fasting heat production to
  account for effects of activity
• Would be higher in grazing animals

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Activity Energy Cost/kg BW

• Standing 2.39 kcal
• Changing position 0.06 kcal
• Walking 0.62 to 6.69 Kcal/km
• Eating 0.60 kcal/h
• Ruminating 0.48 kcal/h

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Work Duration
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Maintenance Energy Components
Maintenance Energy Requirement
Basal Metabolism
Muscular Work
Temperature Regulation
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Temperature Regulation

• When environmental temperature falls below the
  animals lower critical temperature, heat
  production must increase if normal body
  temperature is to be maintained

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Temperature Regulation
Upper Critical Temperature
Lower Critical Temperature
Thermoneutral Zone
Heat Production
Evaporative Loss
EAT
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Temperature Regulation

• Effective ambient temperature (EAT)
• Combination of ambient temperature and how an
  animal perceives ambient temperature
• Thermoneutral zone (TNZ)
• Range of temperature in which animal does not
  have to use body resources to heat or cool
• Lower and upper critical temperature (LCT and
  UCT)
• Greater potential to protect from cold than heat

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Temperature Regulation

• Lower critical temperature is affected by
• Level of feed intake
• Body size
• Tissue insulation (condition)
• Coat insulation

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NEg and NEl

• Amount of energy stored as body tissues or used
  for production (lactation) as a result of feed
  consumption above that required for maintenance
• If total NE gt NEm requirement
• Remaining energy used for production
• Maintenance needs must always be met first

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Net Energy System
Net Energy (NE)
Metabolizable Energy (ME)
Digestible Energy(DE)
Gross Energy (GE)
Heat
Urinary Gaseous Energy
Fecal Energy
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Ruminants Are Less Efficient

• Due to methane production when fermenting either
  fiber or starch
• Heat of fermentation increases losses

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Sources of Energy Loss
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Energy Term Utilization

• TDN sheep, goats, heifers, cows
• DE fish, horses, sheep, goats, rabbits, swine
• ME birds, cats, dogs, sheep, goats, swine
• NEm, Neg growing/finishing cattle
• Nel lactating dairy cattle