1. DETERMINATION OF FEED ENERGY CONCENTRATION PP. 109-120

2. TOTAL DIGESTIBLE NUTRIENTS (TDN)
Traditional system to express digestible energy concentration of feedstuffs
Basis of TDN are physiological fuel values
Nutrient
Heat of combustion, kcal/gm
Heat of combustion of metabolic products, kcal/gm
Nutrient absorption, %
Physiological fuel value, kcal/gm
Carbohydrates
4.1 - 98
4.0
Fats
9.45 95
9.0
Protein
5.65
1.30 92

3. Calculation
Conduct a digestibility trial and determine the apparent digestion coefficient of:
Crude protein
Crude fiber
Nitrogen free extract
Ether extract
Calculate concentration of each digestible nutrient in the diet
Digestible protein (DP), % DM = CP, % DM x CP dig. %
Digestible crude fiber (DCF), % DM = CF, %DM x CF dig. %
Digestible NFE (DNFE), % DM = NFE, %DM x NFE dig. %
Digestible EE (DEE), % DM = EE, %DM x EE dig. %
Calculate TDN
TDN, %DM = %DP + %DCF + %DNFE + (2.25 x %DEE)

4. Equivalence in energy units Limitations of TDN
1 lb TDN = 2000 kcal Digestible Energy
1 kg TDN = 4400 kcal Digestible Energy
Limitations of TDN
Limitations with digestion trials
Errors in chemical analyses
Errors in digestibility trials
Low feed intake increases digestibility
DMI at 3x maintenance reduces TDN by 8%
Underestimates or does not include all energy losses in metabolism
Underestimates energy loss in urine (5%)
Does not include methane gas
End product of rumen fermentation
3 – 10% of feed energy
Does not include:
Work of digestion
Heat of fermentation
Heat of nutrient metabolism
Overestimates the usable energy value of feeds
Particularly of forages
Heat increment

5. CALORIC SYSTEM Energy units
Calorie (cal)
Amount of heat required to increase the temperature of 1 gm of water from 14.5 to 15.5oC
Kilocalorie (kcal) = 1000 cal
Megacalorie (Mcal) = 1000 kcal = 1,000,000 cal
Caloric system subtracts digestion and metabolic losses from the total energy of a feedstuff

6. CALORIC SYSTEM Gross Energy Fecal Losses Digestible Energy
Urine Losses
Gaseous Losses
Metabolizable Energy
Heat Increment Losses
Net Energy
Heat of Fermentation
Heat of Nutrient Metabolism
Retained Energy
Work of Digestion
Maintenance
Lactation
Stored Energy
Growth

7. GROSS ENERGY (GE) Heat of combustion
Total potential energy for the feedstuff
Measure by bomb calorimeter
Burn until completely oxidized
Measure amount of heat released
Fats > Proteins > Carbohydrates
Average ratio
Water and Ash have no energy
GE doesn’t differentiate between availability of energy
Little correlation between GE and usefulness to animal
Corn grain- 4.5 kcal/g
Oat straw- 4.7 kcal/g

8. DIGESTIBLE ENERGY (DE)
Digestible Energy = Gross Energy - Fecal losses
Fecal Losses
Ruminants>Monogastrics
Ruminants-
Can be as great as 60% in low quality forage diets
Monogastrics-
Digestibility of energy increases slightly as body weight increases
Can’t be used to express energy requirements of poultry
Relation to Total Digestible Nutrients
1 lbs. TDN = 2000 Kcal DE
1 kg TDN = 4400 Kcal DE

9. METABOLIZABLE ENERGY (ME)
Metabolizable Energy = Digestible Energy – (Combustible Gas + Urinary Energy)
Must be calculated in a neutral growth animal
Zero nitrogen balance
Protein stored or lost from muscle will distort values
Urine (Urea) ~ 5% of GE
Lost as a result of protein metabolism
Ruminants>Monogastrics
Combustible gases
Ruminants >>> Monogastrics
Primarily lost as CH4 ~ 3-10% of GE
Monogastric losses are small and usually ignored ~ % of DE
Commonly used in poultry and swine diet formulation
Relation to DE
Ruminants
ME, kcal/kg = DE x 0.82
Swine
ME, kcal/kg = DE x ( ( * Protein%))
May overestimate energy value of byproduct feedstuffs

10. NET ENERGY (NE)
The amount of energy that is completely useful to the animal for maintenance, lactation, or growth
Net Energy = Metabolizable Energy – heat increment
Heat Increment- increase in heat lost because of the energy costs of digestion and the metabolic processes
Work of Digestion
Activity, Chewing, & GI contractions
As much as 30% of total heat lost in animals (ruminants)
Low quality forage increases work of digestion
Movement and excitement for meal
Heat of fermentation
Heat released by microbes during fermentation
~ 5-10 % of GE
Low quality forage increases heat of fermentation
Increased lipids decreases heat of fermentation
Heat of Nutrient Metabolism
~10-30% of GE lost
Inefficient use of nutrients during metabolism
Other oxidative reactions that would not be coupled to ATP production
Heat produced during excretion by the kidney
Heat increment may be:
Contribute to thermal regulation in cold climate
Contribute to heat load in warm climate

11. Relationship to ME Beef cattle Swine
NE (maintenance)= NEm = 1.37ME – 0.138ME ME
NE (gain) = NEg = 1.42ME – 0.174ME ME
Swine
NE = x ME x EE x Starch – 0.62 x CP – 0.83 x ADF

12. NEm DETERMINATION Calorimetry Comparative slaughter
Animal placed in animal calorimeter
ME intake and heat production measured
NE, Mcal/kg = (ME intake – Heat production)/DMI
Comparative slaughter
Feed group a common diet for two weeks
Slaughter a portion of a group of animals and grind carcass and organs
Determine energy content of the whole body, E1
Feed several levels of feed for a period of time
Slaughter remainder on animals and grind carcass and organs
Determine energy content of the whole body, E2
RE = (E2 - E1)
NE, Mcal/kg = RE/DMI
Use of NE for maintenance (NEm), body weight gain (NEg), or lactation (NEl) determined by regression

13. Regression equations NE is calculated from TDN corrected for intake
NEl , Mcal/kg = x TDN, %

14. PARTITIONING OF NET ENERGY FOR MAINTENANCE AND GAIN
NEm = HeE/Im
NEg = NEr/(I – Im)

15. NEm REQUIREMENT
Maintenance requirement
The amount of feed energy needed for:
Basal metabolic activities
Body temperature regulation
Physical activity:
Results in zero gain or loss of energy from the body tissues
Requirements:
Beef cattle
NEm = Mcal/EBW0.75
Dairy cattle
NEm = Mcal/EBW0.75
Vary with weight, breed, age, sex, season, temperature, nutritional status, physiological status
Significance in net energy calculations for growing animals
Must always calculate the amount of feed necessary to maintain an animal before calculating how much feed would remain or be needed to achieve a given level of body weight gain

16. NET ENERGY FOR GAIN (NEg)
Net energy remaining after maintenance requirements are met
Net energy is used less efficiently for gain than for maintenance

17. EFFICIENCY OF NE USE FOR LACTATION+
Growth
Energy balance
Maintenance _
Low Energy in Diet High

18. Significance of equal efficiency of energy use for maintenance and lactation
Net energy requirements for dairy cows can be expressed with one value
Net energy for lactation, Nel
Energy requirement for lactation considers
Amount of milk produced
Fat percentage of milk produced

19. COMPARISON OF ENERGY FRACTIONS IN DIFFERENT FEEDSTUFFS
Corn grain
kcal/g
Alfalfa Hay
(midbloom)
Oat Straw
Gross Energy
4.5 --
4.7
Digest. Energy
3.92
2.56
2.21
Metab. Energy
3.25
2.10
1.81
NEm
2.24
1.28
0.97
NEg
1.55
0.68
0.42