ENERGY BALANCE AND SYSTEMS
References
• Blaxter, K. L. 1989. Energy Metabolism in
Animals and Man. Cambidge University
Press
• Kleiber, M. 1975. The Fire of Life. Krieger
Publishing, New York
Also Beef, Dairy, and Sheep NRC
Basics of Energy Use in Mammals
• Simple
• Practical
– Energy systems to predict and monitor livestock
production
– The common thread among human weight loss
systems
ENERGY CONCEPTS
• Energy - “ability to do work”
• Feedstuffs
– protein
– carbohydrates
– lipids
• Physics of energy
– Priestly 1700’s - the flame and the mouse
Priestly and the discovery of oxygen
A candle or an animal
can make good air bad.
Plants restore to the air
whatever breathing animals
and burning candles remove.
Early discoveries of relevance
• Theory of combustion - Both fire and
animals produce the same amount of heat per
unit of CO2
• Heat production /unit of O2 produced is a
more uniform measurement
• 1st law of thermodynamics - energy cannot
be created or destroyed
Hess’ Law of Heat Summation
1. Not concerned with mechanisms or rates of energy change
2. True for living as well as non-living systems
3. Forms basis for bioenergetic investigation even if mechanisms of
action is unknown
FECES
FEED
ANIMAL
URINE
100% OF
GAS
HEAT
MAINTENANCE
PRODUCTION
ENERGY
INTAKE
ATP-ADP CYCLE
FUELS
O2
CO2
H2O
CATABOLISM
ADP
ATP
Pi
MECHANICAL
WORK
Pi
TRANSPORT
WORK
Pi
BIOSYNTHETIC
WORK
Units of Measure
• Calorie - energy required to raise the
temperature of 1 g of water 1 degree C (from
16.5 to 17.5)
–
–
–
–
1 kilocalorie (kcal) = 1,000 calories
1megacalorie (Mcal) = 1,000,000 calories
1kcal/g = 1 Mcal/kg
1 calorie = 4.184 joules
Bomb Calorimeter
PARTITIONING OF ENERGY
Gross Energy (GE)
Digestion loss (fecal)
Digestible Energy (DE)
Urine loss
Combustible gases (CH4)
Metabolizable Energy (ME)
Heat increment (HI)
-heat of fermentation
-heat of nutrient metabolism
Net Energy (NE)
NEm
-basal metabolism
-activity at maintenance
-sustaining body temp
NEg
-retained energy
HEAT LOSS
•BASAL METABOLISM
•VOLUNTARY ACTIVITY
•PRODUCT FORMATION
•THERMAL REGULATION
•WORK OF DIGESTION
•HEAT OF FERMENTATION
•WASTE FORMATION AND EXCRETION
BASAL METABOLISM
•VITAL CELLULAR ACTIVITY
•RESPIRATION
•BLOOD CIRCULATION
•IONIC BALANCE
•TURNOVER OF PROTEINS
RETAINED ENERGY
•TISSUE GROWTH
•LACTATION
•WOOL GROWTH
•HAIR GROWTH
•PREGNANCY
SYNTHESIS OF BODY TISSUES
•FAT contains 9.4 Mcal/kg and 3.8 Mcal/kg is lost as heat
•13.2 Mcal are required to deposit 1 kg fat
•PROTEIN contains 5.6 Mcal/kg (muscle=1.1 Mcal/kg)
•7.4 Mcal are lost as heat (1.5 Mcal for muscle)
•13 Mcal are required to deposit 1 kg of protein
•2.6 Mcal are required to deposit 1 kg of muscle
GROSS ENERGY
•FEED
GE (kcal/g)
•Corn meal
4.4
•Oats
4.6
•Wheat bran
4.5
•Timothy hay
4.5
•Clover hay
4.5
•Corn stover
4.3
•Oat straw
4.4
GROSS ENERGY OF FEEDSTUFF
COMPONENTS
•CARBOHYDRATE 4.2 kcal/g
•FAT
9.4 kcal/g
•PROTEIN
5.6 kcal/g
•ASH
0.0 kcal/g
BACON TORCH
Calorimetry
• DIRECT - direct measurement of heat
production
• INDIRECT - calculation of heat production
from O2 intake, CO2 release and methane
and nitrogen losses
– HE = 3.886 02 +1.2 CO2 -.518 CH4-1.231N
Nitrogen Carbon Balance (Indirect)
• Required data: dry matter, nitrogen, carbon
and energy of feed, feces, urine, methane and
carbon dioxide.
• Assumed:
– 6 g protein/g N
– .5254 g carbon/g. protein
– 5.6 kcal/g protein
N-C balance cont’
• Carbon gained as fat = Foodc – (Fecesc +
Urinec + CO2c + Methanec + Proteinc)
• Fat assumptions:
– 1.307 g fat/ g carbon
– 9.4 kcal/g fat
• Heat productionkcal = Intakekcal - (Feceskcal
+ Urinekcal + Methanekcal +Protein gainedkcal
+ Fat gainedkcal)
Body Size and Metabolism
Kleiber
Armsby Calorimeter
Determination of Nem of timothy
hay by a difference trial
Feeding Feed
level
eaten
(lb)
1
6.2
ME intake Heat prod. Energy
(kcal)
(kcal)
gain
(kcal)
5788
8062
-2296
2
10.2
9544
9812
-268
Diff.
4.0
3766
1748
2028
Armsby (1922)
NEm = 2028/4 = 51 Mcal/cwt
Of historical importance:
1. H = ME - P
2. Development of comparitive slaughter technique
Lofgreen and
Garrett (1968)
NEm DETERMINATION
Item
Alfalfa
Hay
High
Concentrate
Intake at Equilibrium
Heat Prod. an No Feed
NEm of the Feed (kcal/g)
35
43
1.23
23
43
1.87
NEp BY THE "DIFFERENCE TRIAL"
ENERGY
GAIN
NEp
+
0
FEED INCREASE
ACTUAL "DIFFERENCE TRIAL" ON
HIGH CONC. RATION
Item
Feed Intake
Energy Gain
Level of Feeding
Equilibrium Free Choice
23
59
0
40
Differences:
Feed Intake, g
Energy Gain, kcal
---
36
40
NEp of Feed:
kcal per gram
--
1.11
Comparison of Fed and Fasted Steers by
Indirect calorimetry (“head box”)
Fed
Fasted
339
333
Oxygen
197.2
131.0
Carbon dioxide
198.8
96.1
Methane
8.2
1.0
RQ
1.01
0.73
kJ/d per kg BW
147.3
93.7
jJ/d per kg BW0.75
632.6
400.8
Weight (kg)
Gas exchange (1/2 h):
Heat Production
Eisemann and Nienaber (Brit. J. of Nutr. 64:399, 1990)
DIGESTIBLE ENERGY (DE)
•TOTAL DIGESTIBLE NUTRIENTS (TDN)
•1 lb TDN = 2,000 kcal DE
•TDN = DCP + DNFE + DCF + 2.25(DEE)
•Estimated from ADF
•from truly digestible NFC, NDF, CP and FA
•Dairy NRC
• (http://www.nap.edu/books/0309069971/html/)
•pp. 13-27
CONVERSION BETWEEN DE, ME &
NE
•ME = .82DE
•NEm = 1.37 ME - 0.138 ME2 + 0.0105 ME3 -1.12
•NEg = 1.42 ME - 0.174 ME2 + 0.0122 ME3 -1.65
EFFECT OF ENVIRONMENT ON
ENERGY REQUIREMENTS
Lower
Critical
Temperature
Cold stress
Upper
Critical
Temperature
THERMONEUTRAL
ZONE
Heat Stress
Optimum
for
Performance
and
Health
Low
EFFECTIVE AMBIENT TEMPERATURE
High
Lower Critical Temperature
•Coat Description
LCT
•Summer or wet
59
•Fall
45
•Winter
32
•Heavy winter
18
Effective Temperature
Wind Speed
Calm
5
15
30
-10
-10
-16
-25
-46
Temperature
0
10
0
10
-6
3
-15
-5
-36
-26
20
20
13
4
-16
30
30
23
14
-6
*Maintenance Requirements increase .7% for each degree
of cold stress.
NEp (production)
•NEg (gain)
•NEc (conceptus)
•NEl (lactation)
Beef NRC Gain equations
•NEm (Mcal) = .077 WTkg.75 *(environmental adjustment)
•EBW = .891 SBW
•EBG = .956 SWG
•SRW = 478 kg for animals finishing at small marbling
•EQSBW = SBW * (SRW)/(FSBW)
•EQEBW = .891 EQSBW
•RE = 0.0635 EQEBW0.75 EBG1.097
•SWG = 13.91 RE 0.9116 EQSBW-.6837
Using Net Energy for Gain Projection
Step 1. Determine dry matter intake of each ingredient
Lb. as fed
Corn silage
Corn
SBM
15
7
1.5
Total
23.5
X
DM fraction
.4
.85
.9
=
Lb DM
6.0
5.95
1.35
13.3
Using Net Energy for Gain Projection
Step 2. Determine NEm intake
Lb. DM
Corn silage
Corn
SBM
6
5.95
1.35
Total
13.3
X
NEm/lb
.4
1.02
.93
=
NEm
(Mcal)
4.44
6.07
1.26
11.77
Ration NEm (DM Basis) = 11.77Mcal/13.3 lb DM = .89 Mcal/lb
Using Net Energy for Gain Projection
Step 3. Determine NEg intake
Lb. DM
Corn silage
Corn
SBM
6
5.95
1.35
Total
13.3
X
NEg/lb
..47
.70
.63
=
NEg
(Mcal)
2.82
4.17
.85
7.84
Ration NEg (DM Basis) = 7.84Mcal/13.3 lb DM = .59 Mcal/lb
Using Net Energy for Gain Projection
Step 4. Determine Lb of DM for maintenance
1. NEm requirement 500 lb. steer = 4.5 Mcal
4.5 Mcal * environmental adjustment (1.3) =
5.85 Mcal required / .89 Mcal NEm per lb of DM =
6.6 lb. of feed dry matter needed for maintenance
Environmental adjustment (maintenance ratio) for calf fed in
open lot conditions in November in Iowa.
Using Net Energy for Gain Projection
Step 5. Determine energy available for gain
1. 13.3 lb DM intake - 6.6 lb (needed for maintenance) =
6.7 lb. of feed DM available for gain.
2. 6.7 lbs of DM X .59 Mcal/lb (NEg) = 3.95 Mcal available
for gain.
Using Net Energy for Gain
Projection
• Step 6 - Determine weight gain
–
–
–
–
227 kg steer (low choice at 500 kg)
EQSBW = 227 * (478/500) = 217 kg
SWG = 13.91 * 3.95 0.9116 * 217 -.6837 = 1.23 kg/d
ADG = 1.23*2.205 = 2.71 lb/day
Energy Calculations for Dairy Cattle
•NEm = .08 LW.75 - increased for activity
•Growing bulls & heifers have 12% higher req than beef
•NEm = .086 LW.75
•or use beef equations and increase Maint 7-10%
•NEl~NEm because of similar efficiency
•Lactation requirement (Mcal/kg) milk
•= .0969(percent fat in milk)+.36
•Feed Energy Values discounted for level of feeding
•For a comparison of Dairy Energy Systems see:
J Dairy Sci 81:830, 840, 846 (1998) Energy Symposium
Unit decline per multiple of
Maint
Dairy NRC Feed Energy
Discounts
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
= .18 X -10.3
60
65
70
Maintenance TDN
75
80
Energy calculations for Sheep
•Maintenance requirement is lower than beef
•.056 W.75
•Wool has great insulative value
•Fetal number is important (Nep, Mcal/day)
#fetuses
1
2
3
Stage of gestation (days)
100
120
140
.070
.145
.260
.125
.265
.440
.170
.345
.570
1996/2001 Beef NRC Model Objectives:
• Predict net energy requirements across a continuum of
cattle types
• Adjust requirements for physiological state
• Adjust requirements for environmental conditions
• Predict variable lactation requirements
• Predict energy reserves fluxes
• Describe feeds by fermentation characteristics
• Describe rumen and animal tissue N requirements
• Compute variable ME and MP from feed analysis
• Two levels of solution
Maintenance Requirements
Factors affecting Maintenance
•
•
•
•
•
Weight
Physiological State
Acclimatization
Sex
Breed
• Activity
• Heat or Cold stress
– External Insulation
• Coat Condition
• Wind speed
• Hide Thickness
– Internal Insulation
• Condition Score
• Age
Base NEm Requirement
• 77 kcal / (BWkg)0.75
• Adjusted for:
–
–
–
–
Acclimatization
Sex
Breed
Physiological state
• Lactation
• Condition Score
Effect of Condition Score on
Maintenance Requirement
Maintenance Multiplier
120%
115%
110%
105%
100%
95%
90%
85%
80%
1
2
3
4
5
6
7
Condition Score (1-9 scale)
8
9
Energy Requirements vs. Body Weight
NEm Required, Mcal/d
12.00
10.00
8.00
6.00
4.00
2.00
0.00
0
200
400
Body Weight
600
800
NEm Required, Mcal/BW0.75
Energy Requirements vs. Previous Temp.
110
100
90
80
70
60
50
-20
-10
0
10
20
Previous Temperature,
30
O
C
40
Effect of Breed on Energy Requirements
Relative NEm Required
120%
120%
100%
100%
90%
80%
60%
40%
20%
0%
Bos
indicus
Bos taurus
Dairy
breeds
Effect of Lactation on Energy
Requirements 120%
Relative NEm Required,
% of Basal
120%
100%
100%
80%
60%
40%
20%
0%
Nonlactating
Lactating
Maintenance Adjustment for Grazing
(based on a 600 kg cow)
160%
Mainenance Adjustment
150%
140%
Level
Hilly
130%
120%
110%
100%
0.25
0.75
1.25
Forage Availability (T/ha)
1.75
Estimation of Heat Production and Calculation
of Lower Critical Temp (LCT)
• Calculate Feed for Maintenance (FFM)
– NEm Req./ NEm Diet = FFM
• Calculate Feed for Production (FFP)
– DMI - FFM = FFP
• Calculate Net Energy of Production (NEP Tot)
– NEP Diet x FFP = NEP Tot
– For growing & finishing; NEP Diet = NEg Diet
– For other animals; NEP Diet = NEm Diet
• Calculate Heat Production (HP)
– MEIntake - NEP Tot = HP, Mcal
Body Surface Area vs. Body Weight
8.00
Surface Area, M 2
7.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
0
200
400
Body Weight
600
800
Internal Insulation,
Mcal/M 2/OC/d
14
Effect of Condition Score on
Internal Insulation
12
Age, d
10
<30
30-183
184-364
>365
8
6
4
2
0
1
2
3
4
5
6
7
8
Condition Score (1-9 scale)
9
Effect of Wind Speed and Coat Condition
on External Insulation
External Insulation,
Mcal/M 2/OC/d
25
20
15
10
5
0
0
5
10
15
20
25
Wind Speed, kph
Clean & Dry
mud on lower body and sides
some mud on lower body
heavily covered with mud
30
Effect of Wind Speed and Hide Thickness
on External Insulation
External Insulation,
Mcal/M 2/OC/d
35
30
25
20
15
10
5
0
0
5
10
15
20
25
Wind Speed, kph
Thin Hide
Medium Hide
Thick Hide
30
External Insulation,
Mcal/M 2/OC/d
Effect of Wind Speed and Hair Depth on
External Insulation
50
45
40
35
30
25
20
15
10
5
0
0
5
10
15
20
Wind Speed, kph
1 cm
2 cm
3 cm
25
30
Estimation of Heat Production and
Calculation of Lower Critical Temp (LCT)

Calculate Heat Loss (HL)
– HL = HP / SA, Mcal/M2

Calculate Total Insulation (TI)
– TI = EI + II, Mcal/M2/OC/d

Calculate Lower Critical Temp (LCT)
– LCT = 39 - (HL x TI), OC

Calculate Heat Production
– MEIntake - NEP Tot = Heat Production
Additional ME Required,
Mcal/d
Energy Requirements vs. Current Temp.
7
6
5
Assumed SA = 6 M2
4
and TI = 28 Mcal/M2/OC/d
3
LCT = 5
LCT = -5
2
1
0
-30
-20
-10
0
10
Current Temperature,
20
O
C
30
40
Environmental Effects on Maintenance Requirements
Beef Cow Wintering Ration (hay @ .90 mcal ME/lb DM)
Hair Coat Code at
30oF
1
3
Hide
Code
1
2
3
Hair Coat Code at
10oF
1
3
Wind @ 1 mph
1.19
1.19
1.19
1.19
1.19
1.19
1.29
1.29
1.29
1.68
1.55
1.45
Wind @ 10 mph
1
2
3
1.22
1.19
1.19
1.48
1.41
1.34
1.60
1.47
1.36
1.94
1.84
1.75
Environmental Effects on Maintenance Requirements
Typical Calf Wintering Ration ( .35 mcal NEg/lb DM)
Hair Coat Code at
30oF
1
3
Hide
Code
1
2
3
Hair Coat Code at
10oF
1
3
Wind @ 1 mph
1.19
1.19
1.19
1.47
1.37
1.28
1.50
1.36
1.29
2.93
1.80
1.69
Wind @ 10 mph
1
2
3
1.41
1.30
1.21
1.69
1.61
1.54
1.85
1.71
1.60
2.20
2.10
2.01
Environmental Effects on Maintenance Requirements
Typical Finishing Ration ( .62 mcal NEg/lb DM)
Hair Coat Code at
30oF
1
3
Hide
Code
1
2
3
Hair Coat Code at
10oF
1
3
Wind @ 1 mph
1.19
1.19
1.19
1.19
1.19
1.19
1.33
1.29
1.29
1.76
1.63
1.51
Wind @ 10 mph
1
2
3
1.24
1.19
1.19
1.52
1.44
1.36
1.67
1.54
1.42
2.03
1.93
1.83
Growth Requirements
Factors we must account for to predict NEg
required in North America
• Genotype - over 80 types have been identified
• Sex
–
–
–
–
Feedlot steers, heifers & bulls
Replacement heifers
Bulls
Cows
• Implant combinations
• Feeding systems
Relationship between
Body Fat & Grade
Marbling % Body
Score
Fat
USDA
Grade
Trace
Slight
Small
Standard
Select
Choice
25.2%
26.8%
27.8%
Canadian
Grade
A1
A2
A3
NEg Required for Growth
8
0.6 kg/d
1.0 kg/d
1.3 kg/d
7
NEg Mcal/d
6
5
4
3
2
1
0
200
250
300
350
400
Shrunk Body Weight, kg
450
500
% Protein in Gain vs. Rate of Gain
25
0.6 kg/d
1.0 kg/d
1.3 kg/d
% Protein in Gain
20
15
10
5
0
200
250
300
350
400
Shrunk Body Weight, kg
450
500
% Fat in Gain vs. Rate of Gain
90
0.6 kg/d
1.0 kg/d
1.3 kg/d
80
% Fat in Gain
70
60
50
40
30
20
10
0
200
250
300
350
400
Shrunk Body Weight, kg
450
500
Shrunk Body Fat
30
28
% Shrunk Body Fat
26
24
22
20
18
16
14
12
10
200
250
300
350
400
Shrunk Body Weight, kg
450
500
Body Fat vs. Shrunk Body Weight
Slight
Small
Traces
30
28
26
% Body Fat
24
22
20
18
16
14
12
10
200
250
300
350
Shrunk Body Weight
400
450
500
Birth to Maturity - Protein Composition
20
120
%PIG
EBP,kg
100
% Protein in Gain
16
14
80
12
10
60
8
40
6
4
20
2
0
0
200
400
600
Shrunk Body Weight, kg
800
0
1000
Empty Body Protein, kg
18
Birth to Maturity - Fat Composition
100
700
90
80
500
% Fat in Gain
70
60
400
50
300
40
30
200
20
100
10
0
0
200
400
600
Shrunk Body Weight, kg
800
0
1000
Empty Body Fat, kg
600
%FIG
EBF,kg
Non-implanted cattle of Fortin et. al., 1980
(50 heifers, 37 steers and 54 bulls)
1 2 3 4
6
15%
1
2
3
4
5
6
=
=
=
=
=
=
Angus heifer
Holstein heifer
Angus steers
Holstein steers
Angus bulls
Holstein bulls
5%
Empty body fat, %
25%
5
100
300
500
700
900
Empty body weight, kg
Calculation of Equivalent Weight
Actual BW x (SRW / FW) = EQSW
Calculation of Retained Energy
RE = 0.0635 x EBW0.75 x EBG1.097
RE = 0.0635 x EQEBW0.75 x EBG1.097
Calculation of Daily Gain
SWG = 13.91 x RE0.9116 x SBW-0.6837
SWG = 13.91 x RE0.9116 x EQSBW-0.6837