Bioenergetics

animal nutrition exam 1 content

Homeostasis

the state of sustained equilibrium in which all cells and all life forms exists

Bioenergetics

study of energy supply, utilization, and dissipation

Energy

the capacity for performing work

Nutrients

contain chemical energy which is yielded upon metabolism, and used for chemical, mechanical, electrical, or osmotic work

Functions of Energy

Mechanical work

Formation of substrates

Active transport

Transfer of genetic information

Maintenance

C-H bonds release

more energy when broken than C-O bonds

Fats contain

more C-H bonds

Carbs and proteins contain

more C-O bonds

Fats' potential energy is

2.25x the amount of energy than carbs and proteins

Released energy is trapped in

high energy phosphate bonds in the form of ATP

Joule =

kg/(m^2*s^2)

1 calorie is the

heat required to increase the temperature of 1g of water from 14.5 to 15.5 Celsius

1 calorie =

4.184 Joules

The efficiency of conversion of chemical to work energy is

less than 25%

75% of potential energy is lost to

thermal energy (heat)

Energy balance equation

Energy in = energy out + energy to store

Energy eaten is either

used, stored, or excreted

Positive energy balance

Energy in > Energy out

Weight gain

Negative energy balance

Energy out > Energy in

Weight loss

Energy equilibrium

Energy out = Energy in

Weight maintenance

Carbohydrate energy content =

4

Protein energy content =

4

Fat energy content =

9

Alcohol energy content =

7

Total Digestible Nutrient (TDN) system attempted to account for

digestibility, but dos not account for losses associated with fermentation

Total Digestible Nutrients (TDN) is determined by

a digestion trial that calculates the sum of nutrient digestibility

Total Digestible Nutrients (TDN) values lie in between

DE and NE

1 kg TDN = 4.4 Mcal DE

Net Energy System improved on TDN System by

applying the First Law of Thermodynamics

Thermal energy cannot

be converted to any other form

Gross Energy (GE)

Represents total E content of feed using heat of combustion, or the energy released when a feed is completely oxidized

Provides little info on nutrient utilization

Digestible Energy (DE)

DE = GE - fecal energy

Overestimates value of high fiber diets

Losses for ruminants are 40-50% for roughages and 20-30% for grains

Losses for horses are 35-40%

Losses for pigs are 20%

Fecal Energy (FE)

The LARGEST energy loss

Sourced from undigested food and endogenous

Metabolizable Energy (ME)

ME = DE - gas and urine (UE) energy

Used in swine, poultry, and human nutrition

Can be calculated from digestible energy

Urinary Energy (UE)

Total gross energy in urine

Energy from nonutilized and absorbed compounds from food, end products of metabolism, and end products of endogenous origin

Influenced by excess protein in diet

2-3 % of gross energy for pigs, 4-5% in cattle

Urinary energy is calculated by

Collecting the amount of urine (in mammals) produced in 24-48 hours

Uric acid (white bird poop) collected in birds

Gaseous Energy (GE)

Methane, CH4, is the main form lost as gas

Greatest gaseous losses in ruminants, 82% of DE

Too small to be considered for ME in human, pigs, dogs, and chickens

H, CO2, acetone, ethane

Can be directly and indirectly measured

Net Energy (NE)

NE = ME - heat increment (HI)

NEm - maintenance

NEg - gain

NEl - lactation (dairy)

Best indication of energy available for maintenance and production

Used by beef, dairy, and sheep

Impossible to assign a single NE value to a feedstuff (NEm, NEg, NEl)

The horse industry uses

the least sophisticated energy identification system

Heat Increment (HI)

Can represent 25-40% of gross energy intake

2nd largest energy loss

Lowest HI for fat

Highest HI for fiber

Losses of energy as heat

Basal metabolism (CO2)

Muscular activity

Digestion and absorption

Microbial fermentation(huge in ruminants)

Product formation

Waste formation and excretion

Thermal regulation

NEg and NEl are associated with

Production such as tissue growth, storage in products, and work

NEm is associated with

Maintenance such as basal metabolism, activity at maintenance, and sustaining body temp

Maintenance only applies to

mature, nonpregnant, nonlactating animals

Basal Metabolism

Metabolic rate in postabsorptive state, with minimal activity, thermal and psychic stress, needed to sustain life

8 hours post meal

Affected by body size, species, age, previous level of nutrition, climate

The larger an animal

the more heat it produces (linear/curvilinear trend)

Metabolic Body Size

W^0.75

Used to compare animals of different body size or species

Used to determine maintenance energy requirements

Prolonged cold causes

increased basal

heat production

Prolonged heat caused

decreased basal

heat production

Basal heat production declines quickly from

birth to weaning, then slowly to maturity

Effects of exercise on maintenance

requirements depend on

work intensity and duration

NRC (National Research Council animal feed requirements) tables usually add a correction factor of

10% of fasting heat production (higher in grazing animals)

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