iii. energy systems and energy utilization.pdf

8/11/2019 III. Energy Systems and Energy Utilization.pdf

1/6

titled Document

ps://www.msu.edu/~trottier/energy.html[13/08/2014 10:16:16 p.m.]

III. Energy Systems and Energy Utilization

1. Overview of energy systems

Digestible energy:

- Portion of gross energy that is digested is called digestible energy.

- Energy system currently used for swine diet formulation because all DE of feed ingredients

listed in NRC tables are obtained by direct balance studies.

Metabolizable energy:

- Portion of gross energy that is useful for metabolism.

- Energy system currently used in avian diet formulation because fecal and urinary losses occur together.

- Energy system to be used consistently in the future for swine as more and more feed ingredients listed

in NRC tables will be determined for ME by direct balance studies. A lot of the ME of feed ingredients

listed in NRC are derived from DE by calculations.

Net energy:

- Portion of metabolizable energy that is useful for maintenance and productive functions.

- Would be the system of choice for all species, but certainly for ruminants due to diet composition

and rumen fermentation.

- Not practical and very difficult to have a heat production measurement for all level of feed intake

and feed ingredients.

Heat increment:

a) Heat production as a consequence of feeding. Heat increment is useful in winter

for animals raised in a non-confinement system or exposed to environmental temperature below

the thermo neutral comfort zone, but harmful in summer with hot environmental conditions.

b) Composed of:

Energy cost of eating or ruminating

Heat of fermentation (ruminants or hind gut fermenters)

Work of digestion

Work of nutrient metabolism (principle component)

c) Factors affecting Heat increment:

1. Level of feed intake2. Nutritional balance of the diet

3. Composition of feed ingredients


2/6

titled Document


Examples:

1. Forages have higher HI than grains

2. The work of digestion and fermentation is higher with fiber

3. Fat has lower HI than carbohydrate or protein

d) In ruminants, HI may be as high as 40% of ME

HI from protein may be 30% of MEHI from CHO may be 10-15% of ME

HI from fat may be maximum of only 5 % of ME

The "extra caloric effect" of dietary fat is presumed to be:

1. Largely due to the reduced heat increment

2. Improved absorbability of the non-fat portion of the diet by reducing rate of passage

Maximizing energy absorbed from the gut, i.e., reducing fecal energy loss of feedingredients by:

Processing of feed ingredients, for example, decreasing particle size

Decreasing rate of passage (review factors affecting gut motility and rate of passage)

Maximizing the energy necessary for metabolic functions, i.e., minimizing heat lossor heat increment" of feed ingredients by:

Feeding more fat in summer time

Avoiding excess protein intake

Feeding a balanced diet to optimize post-gut nutrient utilization

2. Energy utilization: Maintenance and basal energy expenditure

Basal metabolism:

- The minimum energy expended by an animal under specific conditions of fasting, resting, and thermo-

neutrality.

- The minimum net energy needs

- Function of body surface area, also called metabolic body size: BW.75 kg

**Basal energy metabolism is 70 x (BW.75 kg) kcal across species**

a. Service functions (and % of basal Energy Expenditure)

Nervous system (10-15%)

Heart (9-11%)

Liver (5-10 %)

Kidneys (6-7%)

Respiration (6-7%)

Total 36-50 %

b. Cell "maintenance"

Protein synthesis (protein turnover) (9-12%)


3/6

titled Document


Ion transport (Na/K pump, ATP dependent) (30-40 %)

Lipid re-synthesis (2- 4%)

Total 40-56 %

Productive functions (animal output)

a. Growth- Protein and lipid accretion

b. Milk

c. Eggs

3. Measurement of heat production

1. Factors determining heat production

a) Body size (weight)

b) Heat increment of feeding (a function of ME intake)

c) Activity

d) Work of thermoregulation

Under conditions of "confinement housing" characterized by thermally comfortable conditions

(thermo neutral zone) and minimal activity, work of thermo regulation is nil and HP is determined

by food intake (heat increment of feeding) and body size.

2. Methods of determining energy content or production:

a. Bomb calorimetry (heat of combustion)

To determine the amount of energy in an organic substance or feed

Principle:

O2 + sample= Combustion "heat release"

The rise in H2O temperature leads to calculation of GE value

b. Direct calorimetry (animal heat loss)

- To measure the minimum requirements for maintenance. Animal must be fasted.

Hence also referred as "fasting heat production".

- Pitfall: Not a good measure of energy metabolism in the highly productive animal for which

fasting is "unphysiological".

c. Indirect calorimetry (respiration calorimetry)

- Measures heat production based on gaseous exchange (O2, CO2)

- Uses the concept of R.Q. i.e. Respiratory quotient (CO2/O2)

- Heat produced is based on caloric equivalent of O2 at a particular RQ

- Caloric equivalent of O2 = 1L O2 = 4.839 kcal

HP = Cal equivalent x L O2


4/6

titled Document


4. Determining energy requirements

1. Energy for maintenance (EM)

a) Amount of ME intake which exactly balance HP, and produces no loss or gain

in energy retention

Because of the difficulty in using FHP as a basis for maintenance, EM has been derived

by "extrapolation" to zero energy retention by regression analysis. This is the preferred

method for estimating energy requirements for maintenance, particularly for production

animals

(See figure)

b) Factors affecting maintenance energy

1) Heat stress: mostly a secondary effect resulting from decreased energy consumption and

thus reducing heat produced (HIF)

2) Cold stress: direct effect on HP. As temp decreases, animal increases metabolic activity

and thus HP to maintain homeothermy.

2. Energy for activities

Maintenance requirement presumes that animals are kept under confinement.

Because animals are raised under extensive conditions, maintenance requirement is

increased

due to increased activity.

Because NRC maintenance requirement may be an average of many studies, some costs of

associated with different activities are taken into account to some extent.

3. Energy for production

a) Energy in accreted tissue

-The energy requirement above maintenance is to supply the gross energy of the accreted tissue, i.e. fatand protein.

GE value of protein is 5.64 kcal/g

GE value of fat is 9.4 kcal/g

-As water is associated with protein in the body, as "lean body mass" is accreted, there is a

"bonus" in animal production when protein is deposited; hence the concept that

production of lean meat is more efficient than the production of fat carcass.

b) Energy cost of accreted tissue synthesis

ATP synthesis


5/6

titled Document


- One mole ATP requires 18 kcal of ME

Protein synthesis

- ATP for AA activation, peptide and synthesis, translational processes, etc...

- Cost of protein synthesis is 27.2 KJ ME/g protein

- Theoretical efficiency of protein synthesis is therefore

23.7 / 27.2 = 87%

- Live animal, efficiency of protein synthesis is about 54%

- The reduced efficiency is due to protein turnover, indicating that protein synthesized

is also degraded. So much more protein is synthesized than is actually deposited.

- This cost protein turnover represents a drain on energy utilization and is a source of

metabolic inefficiency in farm animals.

Fat synthesis

- Theoretical efficiency of fat synthesis from dietary lipid is 99%

**This high efficiency indicates that dietary fatty acids can be directly incorporated

into body fat, avoiding energy losses associated with degradation and re-synthesis of

specific fatty acids**

- Theoretical efficiency of fat synthesis from carbohydrate is 85%- Theoretical efficiency of fat synthesis from protein is 69 %

- In the live animal fed a normal mixed diet, efficiency of fat synthesis is about 74%

Summary:

Cost of depositing 1 kg of protein would be 43.9 MJ ME (23.7/.54)

Cost of depositing 1 kg of fat would be 53.5 MJ ME (39.6/.74)

c. Approaches to determine energy requirement for productive function

1. Empirical approach

Based on biological responses to energy intake and involves measurement of:

Daily gain

Feed conversion

Protein deposition or nitrogen retention (lean tissue gain)

**In animal production, the most suitable criterium to evaluate energy requirement

would be the response in nitrogen retention**

The empirical approach in estimating energy requirement is simple to do:

There are 2 types of response when feeding various levels of energy, depending if

you are dealing with a mature animal or growing animal (see f igures)


6/6

titled Document

2. Factorial approach

Sum the known source of energy expenditure and energy retention.

Examples:

Growth:

Kg of lean and fat tissue dissected in carcass at different time points

Lactation:

Amount of milk produced per day and energy content in milk

Gestation:

Body weight gain during gestation and energy content of weight gain (25% fat and 15%

protein)

Energy cost of conceptus

iii. energy systems and energy utilization.pdf

Documents