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Nutrition 202Animal Energetics

R. D. SainzLecture 04

Direct and indirect methods for Direct and indirect methods for estimation of energy utilizationestimation of energy utilization

ME = RE + HE

Direct calorimetry measures heat production (HE) directly

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Long term determination of energy Long term determination of energy expenditureexpenditure

• Free ranging animals• No calorimeters required• Relatively non-invasive

H14CO3- infusion:

measure CO2 entry rate (= production)

H2O + CO2 ↔ H2CO3 ↔ HCO3- + H+

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Double-labeled water can be used to estimate energy expenditure in humans and other animals:

H2O + CO2 ↔ H2CO3 ↔ HCO3- + H+

With injected D218O:

H2O + C18O2 ↔D2CO3 ↔ DC18O3- + D+

D2CO3 : 1 oxygen will be from 18O2 oxygen will be from CO2 = unlabeled

R CO2 = (18O flux – D flux)*(total body water/2)

From: Haggarty & McGRaw, 1988.

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DoubleDouble--label waterlabel water

• 18O flux determined from 18O excretion in urine

• D flux determined from D2O excretion in urine

• The rate of CO2 production can be estimated from the distribution of label;

• This value can be used to calculate heat production, if you know the RQ.

• In adult humans, we can approximate this using the food quotient


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Heart rate measurementsHeart rate measurements

• O2 uptake α heart rate• L O2/minute = beats/minute x L O2/beat• Must be calibrated for each animal & situation• Data logger records HR over 24 hr period• Relatively non-invasive

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Slide courtesy of A. Brosh


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The following equation represents this dependency:

VO2 = HR*SV * (A-V)HR = Rate of Heart beats

VO2 = Oxygen ConsumptionSV = Stroke Volume,

A-V = Arterial – Venous O2 concentration


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AS VO2 = HR*SV * (A-V)and VO2 Per one heart beat=O2Pulse

SV * (A-V) = O2Pulse

S0

VO2 = HR*O2Pulse


Assuming SV and A-V diff are not constant

lead to use regression equation to predict VO2 and EE from HR

(Webster, 1967; Yamamoto et al., 1979; Richards and Lawrence, 1984; Renecker and Hudson, 1985; Purwanto et al., 1990)


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For feedlot cattle, HR during the day is mainly affected by the diet energy and by the time of eating

H diet

L diet

Feeding time


HR

HR

VO2

VO2 & HR of Heifers at rest and during exercise on low and high diets


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y = 16.321x + 67.882R2 = 0.8605

y = 10.959x + 281.22R2 = 0.6135

y = -0.1372x2 + 45.232x - 1230.6R2 = 0.9609

y = -0.0426x2 + 23.509x - 686.34R2 = 0.9061

200

700

1200

1700

2200

2700

20 40 60 80 100 120 140 160 180 200

R L

W L

W H

Animal 2

RH

RH

R=RestW=ExerciseL=Low En' dietH=HighEn' diet

HR (beats/min)

VO2ml/(kgmet.h)

VO2 & HR of one Heifer at rest (R) and during exercise(W) on low (L) and high (H) diets


Pulmonary OPulmonary O22 AA--VV

• Animals are surgically prepared with indwelling O2-sensing catheters and blood flow metering cuffs around pulmonary artery and vein

• O2 uptake = BFR (mL/min)*([O2]ven - [O2]art)• Instantaneous measurement• Extremely invasive

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Measurement of REMeasurement of RE

ME = RE + HE

• Longitudinal studies

• Comparative slaughter

• RE = final body energy – initial body energy

• Initial and final body energy contents are determined by taking representative samples of body tissues and subjecting them to chemical analyses and/or to bomb calorimetry

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Comparative slaughterComparative slaughter

• Advantages:– Direct estimation of recovered energy– Requires no assumptions about efficiencies of deposition, etc.– Doesn’t require sophisticated animal calorimeters

• Disadvantages:– Measurements must be made over long periods of time– Low precision often requires larger numbers of animals– Difficult to obtain accurate estimates of initial composition

• Initial composition:– Sample a representative group at the beginning of the

experiment– Determine their composition– Apply this estimate to the final group(s)

SizeSize

• Weight*

• Length

• Height

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CompositionCompositionThe main chemical components of the body

are water, fat, protein and ash:

Lean animal

60%15%

20%

5%Fat animal

45%

37%

15%3%

Water

Fat

Protein

Ash

Measuring body compositionMeasuring body composition

• Direct– Kill, grind, sub-sample and analyze

• Indirect methods (in vivo)– Non-invasive (varying degrees)– Non-destructive

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External measurements:– Weight– Height– Body mass index = W/H2 (kg/m2)


The relationship between BMI and body composition varies between sexes, racial groups, ages, and levels of physical fitness. Shaquille O’Neal is classified as obese by this measure…

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External measurements:– Weight– Height– Body mass index = W/H2 (kg/m2)– Subcutaneous fat» Skinfold thickness» Imaging techniques


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• Imaging techniques

• Depend on the statistical relationship between tissue images and total body composition

• Ultrasound

• Magnetic resonance

• Dual-energy X-ray absorptiometry (DEXA)

Ultrasound equipmentUltrasound equipment

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Scanning locations for ultrasound measuresScanning locations for ultrasound measures

Rump fatRump fat –– ““P8P8””

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Measurement of ribeye areaMeasurement of ribeye area

Ribeye Ribeye –– longissimus dorsi musclelongissimus dorsi muscle

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Ribeye Ribeye –– longissimus dorsi musclelongissimus dorsi muscle

Steer 85 – young & lean

Steer 85 – older & fatter

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The regression equation is

Body Energy = - 523 + 2.70 x (Shrunk Wt) + 68.6 x (Ultrasound Backfat)

Sy·x = 80.12

R2 = 78.9%

R2(adj) = 77.9%

Volumetric techniquesVolumetric techniques

• Depend upon the difference in density (mass/volume) of fat (± 0.9 kg/L) and lean (± 1.1 kg/L) tissue

• Underwater weighing • Archimedes principle, specific gravity• Problem of residual air in lungs

• Whole-body plethysmograph• Place body in closed chamber, change chamber volume and

measure changes in pressure• PV = nRT• Same problem of residual air, surface effects

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where TC (temperature coefficient) is the density of water at tank temperature ÷density of water at carcass temperature.

Then,Empty body energy (Mcal/kg) = 47.58 –

41.97 Density

R = -0.95, SEE = ± 0.15

)*( TCwaterinWtairinWtairinWtDensity

−=

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The Bod PodTM The Pea PodTM

Performance of Pea Performance of Pea PodPodTMTM on beef tissue on beef tissue phantomsphantoms

Sainz & Urlando, 2002

0 10 20 30 40%FAT ADP (%)

0

10

20

30

40

%FA

TCA

(%)

0 10 20 30 40Mean of %FAT ADP and %FAT CA

-3

-2

-1

0

1

2

3

%FA

TA

DP -

%FA

T CA

(%)

0 10 20 30 40-3

-2

-1

0

1

2

3

0 10 20 30 40-3

-2

-1

0

1

2

3

0 10 20 30 40-3

-2

-1

0

1

2

3

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• Electrical properties• Depends on the differences in electrical conductivity of

fat (low) and lean (high) tissues • Bioimpedance analysis

– pass a small current through the body, resistance is a measure of total body H2O

– low precision (± 10%); acceptable for medical purposes?

• Total Body Electrical Conductivity (ToBEC)

Bioelectric Impedance ToBEC

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• Body water space• Depends on the inverse relationship between body

water and body fat• Relative proportions of body water, protein and ash

vary little, fat varies a great deal • Requires a tracer that distributes rapidly and uniformly

into all body water compartments, e.g.– D2O– TOH– Urea– Antipyrine

Body water spaceBody water space

0

10

20

30

40

40 45 50 55 60 65

Body water, %

Bod

y fa

t, %

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• Example: assume lean and fat animals, both weighing 100 kg;– Inject 10 mL of D2O– Allow to equilibrate– Sample body fluid

• Body water (L) = Dose (mL) / Concentration (mL/L)

• Body water % = 100 x body water (L) / body wt (kg)

• Then: use previously determined ratios of water:protein:ash, e.g. 12:4:1, so that

• Body protein % = body water % ÷ 3

• Body fat % = 100 – [body water % * (12+4+1)/12]

Lean Fat

Body wt, kg 100 100

Body fat, kg 15 37

Body water, L 60 45

D2O concentration, mL/L 0.166 0.222

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