DETERMINATION OF FEED ENERGY
CONCENTRATION
PP. 109-120
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
4.0
• 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)
• Equivalence in energy units
– 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
Heat increment
– Overestimates the usable energy value of feeds
• Particularly of forages
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
CALORIC SYSTEM
Gross Energy
Fecal Losses
Digestible Energy
Urine Losses
Gaseous Losses
Heat Increment Losses
Work of
Digestion
Heat of
Fermentation
Heat of
Nutrient
Metabolism
Metabolizable Energy
Net Energy
Maintenance
Retained Energy
Lactation
Stored Energy
Growth
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 2.5 - 1.7 - 1.0
• 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
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
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 ~ 0.13.0% 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 (1.012 - (0.0019 * Protein%))
• May overestimate energy value of byproduct feedstuffs
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
Relationship to ME
Beef cattle
NE (maintenance)= NEm = 1.37ME – 0.138ME2 + 0.0105ME3 - 1.12
NE (gain)
= NEg = 1.42ME – 0.174ME2 + 0.0122ME3 - 1.65
Swine
NE = 0.726 x ME + 1.33 x EE + 0.39 x Starch – 0.62 x CP – 0.83 x ADF
NEm DETERMINATION
• Calorimetry
– 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
• Regression equations
– NE is calculated from TDN corrected for intake
• NEl , Mcal/kg = 0.0245 x TDN, % - 1.12
PARTITIONING OF NET ENERGY FOR
MAINTENANCE AND GAIN
• NEm = HeE/Im
• NEg = NEr/(I – Im)
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 = 0.077 Mcal/EBW0.75
– Dairy cattle
• NEm = 0.080 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
NET ENERGY FOR GAIN (NEg)
• Net energy remaining after maintenance
requirements are met
• Net energy is used less efficiently for gain
than for maintenance
EFFICIENCY OF NE USE FOR
LACTATION
Energy balance
Lactation
+
Growth
0
Maintenance
_
Low
Energy in Diet
High
• 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
COMPARISON OF ENERGY FRACTIONS
IN DIFFERENT FEEDSTUFFS
Corn
grain
kcal/g
Alfalfa Hay
(midbloom)
kcal/g
Oat Straw
kcal/g
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