Transcript Energy

Energy
Energy is the potential to do work. Energy
can be converted from one form to another
but can not be created or destroyed.
Units (Nutrition)
calorie is most often used in US = heat
required to raise the temperature of 1 g
of water from 16.5 to 17.50 C.
1 calorie = 4.184 joules
1 kcal = 1,000 calories
1 Mcal = 1,000 kcal
Energy
Gross energy = Energy (E) in the feed
measured in a calorimeter
Digestible energy (DE) = E in the feed - E in
the feces.
Measured in digestion trials
Metabolizable energy (ME) = E in the
feed - (E in the feces + E in urine + E in
combustible gases)
Measured in digestion studies + collect
gas loss
Energy
Retained energy (RE) = ME - heat loss (HE)
Measured in
1) Calorimeter study
Measure energy intake and energy
losses
2) Comparative slaughter experiment
Measure energy intake and energy
retained in gain
Energy
Metabolizable energy used for:
1) Maintenance (heat loss)
2) Production (gain in body mass, milk,
reproduction, wool)
Feed values
HE at zero feed intake is energy required for
maintenance
Feed intake when RE = 0 is feed required for
maintenance (Im)
NEm = HE/Im
NEg = RE/(I-IM)
Energy
+
RE, 0
Mcal
_
NEg
Nm
Maintenance
ME intake, Mcal
Energy Value of
Body Reserves
Energy mobilized, Mcal = 9.4*kg mobilized
fat + 5.7*kg mobilized protein
During mobilization 1 Mcal of RE = 0.80 Mcal
diet NEm
During repletion 1 Mcal of NEm = 1 Mcal
of RE
Equations to Estimate
Energy Requirements
of Beef Cattle
Maintenance
NEm, Mcal/d = 0.077SBW.75
SBW = Shrunk body wt, kg
Equations to Estimate
Energy Requirements
of Beef Cattle
Adjustments in maintenance requirement:
20% greater for Holstein
Steers and heifers similar
15% greater for bulls
20% greater for lactating cows
Similar for all ages
Effect of previous temperature
Effect of activity on pasture
Energy Required for
Maintenance
Effects of environmental temperature:
Zone of thermal neutrality: Animal does
not have to expend energy to maintain
body temperature.
Energy Required for
Maintenance
Lower critical temperature: Temperature at
which animal begins to use energy to
maintain body temperature.
Affected by hair coat, hide thickness, hair
coat dry or wet, body condition
Upper critical temperature: Temperature at
which animal begins to use energy to
maintain body temperature.
Affected by hair coat color, body condition
Equations to Estimate
Energy Requirements
of Beef Cattle
For ration formulation RE is estimated
from quantity of feed remaining after
accounting for feed needed for
maintenance.
Plant Cell
PRIMARY
WALL
SECONDARY
WALL
CELL
CONTENTS
•PROTEIN
•SUGARS
•STARCH
•PECTINS
•FATS
CROSS SECTION
Inside
SECONDARY WALL
NEUTRAL
DETERGENT
FIBER (NDF)
HEMICELLULOSE
LIGNIN
CELLULOSE
PRIMARY WALL
OUTSIDE
ACID
DETERGENT
FIBER (ADF)
Dry Matter Digestibility (%)
Forage ADF and
Dry Matter Digestibility
69
67
65
63
61
59
57
28
29
30
31
32
33
34
35
Forage ADF (%)
Adapted from Miller et al. (1991)
Inside
SECONDARY WALL
NEUTRAL
DETERGENT
FIBER (NDF)
HEMICELLULOSE
LIGNIN
CELLULOSE
PRIMARY WALL
OUTSIDE
ACID
DETERGENT
FIBER (ADF)
Dry Matter intake (% of BW)
Forage NDF and
Dry Matter Intake
3.5
3.0
2.5
2.0
1.5
1.0
.5
.0
38
42
46
50
54
58
62
66
70
74
78
Forage NDF (%)
Adapted from Mertens (1985) & Burns et al. (1997)