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ESTIMATION OF DENSITY OF LIVE PIGS BY
AIR DISPLACEMENT AND HELIUM
DILUTEQN PEGCEWRES

Thesis for ”‘49 Degree of pin. D.

IICFECN SA: $21“?
Richard Henry Gnaeciinger

1952

This is to certify that the

thesis entitled

ESTIMATION OF DENSITY OF. LIVE PIGS BY Am

DISPLACEMENT AND HELIUM DILUTION PROCEDURES
presented by

Richard Henry Gnaed inger

has been accepted towards fulfillment
of the requirements for

Ph. D. degree in Food Science

{MW

Major professor

Date May 111 1962

0-169

 

  
     

  

L 15 R A R Y
Michigan State

University

 

ABSTRACT
ESTIMATION OF DENSITY OF LIVE PIGS BY AIR

DISPLACEMENT AND HELIUM DILUTION PROCEDURES
By Richard Henry Gnaedinger

The densities of 24 market weight pigs (181-220 lbs.) were deter-
‘mined using the air displacement and helium dilution methods of measuring
body volume. The densities thus obtained were correlated with the water,
ether extract, protein, and ash content of the live animals in an attempt
to objectively predict body composition.

The air displacement method consisted of enclosing the animals in
an air tight chamber of known volume and subjecting it to a known reduction
in pressure. Body volume was then computed from the resultant pressure-
volume relationships according to the gas laws of Boyle and Charles. The
densities obtained by air diaplacement ranged from 0.975 to 1.222 with a
mean of 1.075. The major difficulties involved in the air diaplacement
method appeared to be the lack of control of temperature and relative
hunidity. Of these two variables, relative hunidity appeared to have the
greater influence on the results. The activity of the animals in the
chamber undoubtedly influenced the results somewhat, but the magnitude
of this effect could not be ascertained.

The helium dilution method consisted of enclosing the animal in a
chamber and injecting and mixing a known quantity of helium in the air

Space around the animal. The resultant helium concentration in the cham-
ber was proportional to body volume. Helium concentration was ascertained

using the thermal conductivity principle for gas analysis. The density

Richard Henry Gnaedinger

values obtained by helium dilution ranged from 0.940 to 1.114 with a

mean of 1.017. The inaccuracies involved in the helium dilution method
were caused by the activity of the experimental animals inside the cham-
ber. Changes in temperature, relative humidity, and the composition of
the reapiratory gases due to the animal's respiration.were the major
sources of error. Carbon dioxide accumulation and oxygen depletion were
detected by the helium analyzer and the effect was superimposed on the
helium concentration curve. Thermal expansion of the air-helium mixture
and the eXpiration of the animal resulted in a loss of some helium from
the chamber. An expedient correction can be made for these sources of
error, if all the variables remain constant or if they change at a con-
stant rate during the course of a run. However, the animals in this study
exhibited various degrees of activity, and thus caused fluctuations in the
variables during a run.

The density values obtained by both air displacement and helium
dilution were correlated non-significantly with.percent carcass water,
ether extract, protein, and ash. The density values obtained by air dis-
placement were correlated non-significantly with those obtained by helium
dilution. Although neither method of measuring body volume was reliable,
the helium dilution technique was more predictive of body composition than
the air displacement technique.

The average chemical composition of the live pigs used in this study
was: 49.03% water (42.11 to 53.17%), 33.00% ether extract (27.37 to
41.13%), 13.69% protein (12.44 to 14.57%), and 2.72% ash (2.20 to 3.12%).
The results of the chemical analysis showed that the dressed carcass con-

tained 74.08% of the water, 89.79% of the ether extract, 76.13% of the

Richard Henry Gnaedinger

protein, and 79.11% of the ash in the whole animal. The carcass, empty
intestines, caul fat, and head combined contained 98.77% of the total
ether extract in the whole animal. The carcass and head combined con-
tributed 93.50% of the total ash content of the animal. The results of
the chemical analysis also suggested that average values for the composi-
tion of the hair and blood could be used without introducing any appre-
ciable error in the analysis of the total animal.

The relationship between percent ether extract of the carcasses and
of the empty bodies for this group of animals was r = 0.991. The re-
gression equation for estimating percent ether extract of the empty body
from total body water was: i - 97.16 - 1.298X (3x.y - i 0.527., r = -o.971).
The relationship between the percentages of water and ether extract in
the empty bodies was computed according to the equation: T - 96.40 -
1.297X (Sx.y = i 1.5%, r - -0.974) where X = percent water in the empty
body.

A highly significant relationship was found between the percent
ether extract of the empty body and the percent water of the ether extract-
free empty body (r = -0.597). The significance of this relationship
suggested that the group of animals used in this study was not chemically
mature, and that body fat could not be validly predicted from the water

content of the fat-free body.

ESTIMATION OF DENSITY OF LIVE PIGS BY AIR

DISPLACEMENT AND HELIUM DILUTION PROCEDURES

By

Richard Henry Gnaedinger

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Food Science

1962

ACKNOWLEDGMENTS

The author is most grateful to Dr. A. M. Pearson, Professor of Food
Science, for his guidance in selecting the author's course of study and
directing the research project. He is also grateful to Dr. E. P. Reineke,
Professor of Physiology, for his guidance of the research project.
Gratitude is also expressed to the other members of the author's guidance
committee, Dr. B. S. Schweigert, Chairman of the Department of Food
Science, and Dr. R. W. Luecke, Professor of Biochemistry, for their
guidance in selecting the author's course of study.

The author is thankful to Mrs. Dora Spooner and Mrs. Joan Suden for
their assistance in the chemical analysis of the samples. Thanks are
due also to Mr. James Sanislo, electrical technician, Department of
Electrical Engineering, for his advice on the electrical circuitry in-
volved in the research project. The author wishes to express his thanks

to Mrs. Beatrice Eichelberger for her typing of this thesis.

ii

I.

II.

III.

IV.

TABLE OF CONTENTS

INT MD UC T ION . O O O O O O O O O O O O O O O O I I O O

A.

B.

Application of Archimede's Principle to Studies on
comPOSition O O O O O O O I O O O O O O O O I O 0

Experimental Objectives . . . . . . . . . . . . .

REVIEW OF LITEMTURE O O O O O O O O O O O O O O O O 0

Determination of Volume by Air DiSplacement . . .

Determination of Volume by Helium Dilution . . . .

Estimation of Total Body Fat Content from Live Body

Den31ty O O O O O O O O O O O O O I O O O O O O O

BEE MNT& PROCED URE . O O O O O O O O O O O I O C O

A.

B.

D.

Experimental Animals . . . . . . . . . . . . . . .
Determination of Body Density by Air Displacement
1. Apparatus . . . . . . . . . . . . . . . . .

2. Procedure . . . . . . . . . . . . . . . . . .
Determination of Body Density by Helium Dilution .
1. Apparatus . . . . . . . . . . . . . . . . .

2. Procedure . . . . . . . . . . . . . . . . . .

Sampling and Analysis of Carcass . . . . . . . .

RESULTS AND DISCUSSION . . . . . . . . . . . . . . . .

A.

Relationships between Various Density Values . . .
Errors in Measuring Density by Air Displacement .
Errors in Measuring Density by Helium Dilution . .
Body Composition Relationships . . . . . . . . .

iii

12

14

17

17

17

17

20

22

22

28

34

38

38

40

43

48

V.

VI.

VII.

SUMMARY . . . . .

LITERATURE CITED .

APPENDIX . . . . .

iv

LIST OF TABLES

Table Page

I. Summary of correlation coefficients . . . . . . . . . . . . 39

II. Analysis of variance of values obtained for the volume of
the empty animal chamber . . . . . . . . . . . . . . . . . 41

III. Contribution of each component to the whole animal as
percentages of total moisture, ether extract, protein,
and a Sh O O O O O I O O O O O O O O O O O O I O O O O O 0

IV. Percentages of moisture, protein, and ash in the fat-free
bOdy and fat-free Carcass o o o o o o o o o o o o o o o o o~ 55

LIST OF FIGURES
Figure Page
I. Diagrammatic drawing of the apparatus designed to

‘measure body volume by air displacement . . . . . . . . 11

II. Schematic of apparatus designed to measure body volume
by air displacement . . . . . . . . . . . . . . . . . . 18

III. End view of Open animal chamber showing location of
baffles I I I I I I I I I I I I I I I I I I I I I I I I 19

IV. Schematic of helium metering system . . . . . . . . . . 23

V. Schematic of helium analyzer showing location of
resistance decades . . . . . . . . . . . . . . . . . . 26

VI. Schematic of oil bath and accessories . . . . . . . . . 27

VII. Schematic of gas sampling system . . . . . . . . . . . 29

VIII. Schematic drawing of a typical helium concentration
curve I I I I I I I I I I I I I I I I I I I I I I I I I 31

IX. Graph of deflection values versus helium concentration
at both reference volumes . . . . . . . . . . . . . . . 33

vi

10.

11.

12.

13.

LIST OF APPENDIX TABLES

Page

Summary of body weight and density values . . . . . . . . . . 62

weights of various frozen body components, hot dressed
carcass, and live animal . . . . . . . . . . . . . . . . .

Percent moisture of the animal body components (frozen) . .
Percent ether extract of the animal body components (frozen)
Percent protein of the animal body components (frozen) . .
Percent ash of the animal body components (frozen) . . . .

Percent moisture contributed by each component to total
bOdy mOiSture I I I I I I I I I I I I I I I I I I I I I I I

Percent ether extract contributed by each component to total
ether extract . . . . . . . . . . . . . . . . . . . . . . .

Percent protein contributed by each component to total body
protein I I I I I I I I I I I I I I I I I I I I I I I I I I

Percent ash contributed by each component to total body ash

Composition of ether extract-free, contents-free body and
ether extract-free carcass . . . . . . . . . . . . . . . .

Percentage composition of whole animal and hot dressed
carcass I I I I I I I I I I I I I I I I I I I I I I I I I I

Length, backfat thickness, and dressing percentage data . .

vii

63
64
65
66

67

68

69

70

71

72

73

74

INTRODUCTION

Application of Archimede's Principle to Studies on Body Composition

The composition of an animal body during any time in life is a sub-
ject of great interest to research workers in the field of animal biology.
An objective method of accurately predicting the composition of a live
animal has been sought for a long time. To date the only accurate
measure of composition, namely chemical analysis, requires that the
animal be sacrificed. If an objective measure with this degree of
accuracy could be obtained without sacrificing the animal, its potentia-
lities would be great. For instance, the composition of animal gains at
any time during growth and development could be measured. Also, its
medical applications would be of equal value. The composition of the
human body could be followed during conditions such as growth, exercise,
starvation, and disease.

Archimedes (287-212 B.C.) observed that the composition of an object
could be ascertained by determining its specific gravity. He deduced
that a body immersed in a fluid is buoyed up with a force equal to the
weight of the displaced fluid (1). Thus, the principle of hydrostatics
can be used to characterize various solid objects as to their volume,
density, and specific gravity. The volume of an object can be determined
directly by immersing it in a fluid and measuring the volume of fluid
that it displaces. Its density is determined from the ratio of its mass
to volume, and its Specific gravity is then computed from the ratio of
its density to the density of water.

Archimedes' principle is theoretically equally applicable to the
characterization of animate as well as inert objects. For animate objects,

-1-

-2-

namely live animals, the property of most importance is density, since
body composition can theoretically be predicted from the relative value
of this pr0perty. This is made possible by considering the animal body
to be composed of an invariable component of density greater than unity
and a variable component of density less than unity. Thus, as the per-
centage of the variable component, namely fat, increases or decreases, a
corresponding inverse relationship exists in the value of the animal's
density.
Experimental Objectives

As was previously stated, the volume of an object can be determined
directly by measuring the volume of fluid that it displaces. Similarly,
volume can be determined by measuring the volume of the gas that it dis-
places. Hence, the first and most important objective of this study
involved the measurement of the volume of gas displaced by live hogs
using two methods of measurement, air displacement and helium dilution.
The second objective was to establish the relationship between body
composition and density for a group of hogs. The third objective was to
evaluate each method for its accuracy and precision for measuring body

volume and predicting body composition.

REVIEW OF LITERATURE
Determination of Volume by Air Displacement.

The measurement of body volume by air diSplacement apparently had
its beginning some 80 years ago when Jaeger (2, 3) suggested a relation-
ship between corporeal density and health. He attempted to measure the
volume of an object by enclosing it in an air tight chamber, which he
called a Kopp Volumeter. This chamber was constructed in such a way so
that its volume could be changed by a known.amount. Then, with an object
of unknown volume (V0) placed inside the chamber of initial volume (V)
at atmOSpheric pressure (P) and V changed to (V; AV), Vo was computed

from the resultant pressure change (15V) with the following equation:

VP
Vo :- (V - AV) m (1)

This procedure was reported as being accurate for determining the
volume of inert objects, but complications would result with live animals
due to their respiratory exchanges and the increasing air temperature.
Inspection of equation 1 reveals that it could not be used to compute
the volume of live animals accurately, because it contains no factors to
compensate for these inherent variables.

Some 20 years after Jaeger's work, Pfaundler (4) attempted to mea-
sure the net volume of a child cadaver, which he defined as the total
body volume minus the volume of gas in the respiratory and digestive
tracts. He constructed a felt-insulated, brass chamber, 25 cm. wide and
55 cm. long, which was sealed at one end and contained a removable door
at the other. A thermometer was used to record the temperature of the

air in the chamber, and a sulfuric acid manometer, which could be read

-3-

-4-

to i 0.1 mm., was used to record pressure. The procedure for determining
volume consisted of changing the pressure of the air inside the chamber
by a known amount without altering the actual volume of the chamber it-
self. Net volume was then taken as an average of two determinations,
one being made at a pressure greater than atmOSpheric and the other at a
pressure less than atmOSpheric. This entire procedure was repeated
several times until constant readings were obtained. From 16 observa-
tions made on the volume of a cadaver by this method, an average value
of 1.143 was obtained for its density. The major disadvantage with this
procedure was the great length of time that was required to establish
thermal equilibrium between the cadaver and air after each pressure
change. The time required to make one reading was about 1.5 hours.
During the procedure of making a reading, temperature differences up to
1°C were observed but were regarded as insignificant. However, an error
of this magnitude, when made at a temperature of 25°C, will change the
computed volume of a 50 liter object by about 4%.

‘Murlin and Hoobler (5) reported the use of Pfaundler's procedure
to determine the density of subjects in a study on the energy metabolism
of normal and marasmic children. Their results are tabulated below. The
results of this study showed that weight was more closely related to
metabolism.than was surface area. The relationship was even better when

weight was multiplied by density.

Density of children as determined by air displacement

 

 

Weight

Subject Age gms. Density
Normal boy 2 mo. 5690 0.973
Nonmal boy 2 mo. 4634 1.034
Normal boy 2 mo. 4350 1.003
Undernourished boy 3 mo. 4115 1.006
Undernourished boy 3 mo. 4147 1.005
AtrOphic boy 3 me. 2462 1.108
Atrophic boy 3 mo. 2515 1.118
Normal girl 10.5 mo. 9465 1.026
Normal boy 12 mo. 9555 1.029

 

Pfleiderer (6) determined volume with an apparatus consisting of
two interconnected chambers, one large enough to hold the subject and
the other of suitable size to be used as a standard for altering the
pressure of the air inside the subject chamber. Pressures greater than
atmospheric were used in his procedure, and the amount of compression
was controlled by filling the standard chamber with water, thereby forc-
ing its air into the other chamber. The resultant pressure rise due to
the introduction of the air was then directly proportional to the size of
the object placed inside the subject chamber. Thus, the difference be-
tween the pressures obtained with an empty and an occupied chamber was
then used to compute the volume of the subject. 'With this procedure,
Pfleiderer was able to compute body volumes with a mean error of 1 to 2%.
Pfleiderer (6) enumerated a number of precautions that must be ob-
served when determining the volume of live animals. The vapor pressure
of water had an effect on the final pressure of the chamber. He attempted
to minimize this effect in his procedure by keeping the air saturated at
all times. Reapiration by the animal effected a gradual change on the

final pressure due to the changing partial pressures of the reapiratory

gases. This degree of change was in turn dependent on the basal metabo-
lism of the animal. He also observed that a pressure of 200 mm. of water
was easily tolerated by live animals. Consequently, he noted that if
higher pressures could be used, the maximum percentage error in computing
the final body volume, due to errors in reading pressure, would be re-
duced. Finally, he noted that a small ratio of chamber to subject volume
would effect a smaller error in the final computed volume.

Kohlrausch (7) suggested that the fat and ash content of an animal
could be determined from density, provided the amount of protein was
known. He constructed an insulated steel chamber (80 x 30 x 25 cm.) of
60 liters capacity with a removable door containing a rubber gasket to
make a hermetic seal. The chamber was fitted with valves arranged so
that moist air could be introduced into the chamber after it was partially
evacuated. Another valve served as a passage for introducing a given
quantity of air into the chamber. Pressures greater than atmOSpheric
were used in this procedure to make the density determinations. The
compression was accomplished by displacing a volume of air with a known
quantity of water, similar to the procedure in the method of Pfleiderer.
A water manometer was used for recording pressure changes. ‘With this
procedure, Kohlrausch was able to compute the volume of inert objects
‘with great accuracy and precision. He subsequently measured the volumes
of four dogs and obtained a range of 1.046 to 1.074 for their computed
densities. However, no correlation between density and fat content, as
measured by chemical analyses, was reported, but the fat content of these
dogs ranged from 6.2 to 12.2% of body weight. Likewise, the precision

with which the Volume of the dogs was measured was not reported.

In a subsequent experiment, Kohlrausch (8) took one dog, not sacri-
ficed in the previous experiment, and subjected it to several months of
heavy work on a treadmill and again determined its density and active
muscle mass (from basal metabolic rate). Its density increased from
1.054 to 1.074. The active muscle mass increased from 1676 to 1750 grams,
and it was estimated that fat content decreased from 1217 to 609 grams.
The body weight of the dog also decreased from 10,805 to 9060 grams.

Bohnenkamp and Schmgh (9) measured the body volume of humans by a
procedure essentially the same as those described above. Instead of
compressing the gas inside the chamber with air, they injected a known
quantity of oxygen. Their theory was based on the fact that the oxygen
would distribute itself equally throughout the respiratory passages,
which are not part of the solid body mass. No mention was made, however,
of the extent of pressure changes caused by the consumption of the in-
jected oxygen. Corrections for temperature changes were made in computing
body volume, but vapor pressure corrections were eliminated as saturated
conditions were maintained inside the chamber. The results reported were
average density values. For males the average was 1.095, and for females
1.07, with extreme single values ranging from 0.98 to 1.13.

Noyons and Jongbloed (10) criticized the method of Bohnenkamp as
being very difficult to use routinely, even though its principle of
Operation.was satisfactory. They stated that the method required an
accurate knowledge of temperature, relative humidity, and the degree of
gasous exchange due to reSpiration. Furthermore, the Operation required
the assistance of several peeple, and the calculation of density from
the experimental data was quite tedious. Consequently, these investiga-

tors devised a method that theoretically would allow the determination

of density as a function of weight and pressure only. The procedure
consisted of weighing the subject very accurately in an atmosphere of
two different pressures, and then the difference in weight, after cor-
recting for losses due to insensible perspiration, gave an indication of
body volume and density.

In a subsequent investigation, Jongbloed and Noyons (11) measured
the body volume of humans with the apparatus described above. The results
showed a mean density of 1.080 r 0.007 for 20 determinations made within
several weeks on the same person. They noted also that pressures greater
than atmOSpheric were more comfortable to the subjects than pressures
less than atmOSpheric.

In all of the above mentioned procedures, the greatest difficulties
in measuring volume seem to be due to gradual changes in temperature,
relative humidity, and composition of respiratory gases. In view of this,
wedgewood and Newman (12) pr0posed the use of imposing a sine wave of
changing volume on these variables. They also indicated that the proce-
dure would be easy to execute. Unfortunately, no details of their appar-
atus are available, and apparently they have temporarily abandoned their
project.

Liuzzo gt a1. (13) constructed an apparatus that was used to measure
body volume of guinea pigs. It consisted of two desiccator jars, each of
2600 m1. capacity, that could be interconnected 6r separately connected
to the atmOSphere with a valve. Each jar contained a thermistor for
recording temperature, and some suitable arrangement for maintaining the
air inside each chamber in a saturated condition. One jar, which was

used as the standard, was connected to a vacuum pump with a suitable

valve arrangement so that it could be partially evacuated. A U-tube
mercury manometer was used to record pressure. Pressures less than at-
mOSpheric were used. Instead of compressing the air inside the subject
chamber, it was decompressed by a known amount, the degree of which was
determined by the value of the initial vacuum in the standard chamber.
The equation used to compute the volume of a subject (V0) is given below.
This equation includes a factor which compensates for temperature changes
in the standard chamber, but no such correction factor for the subject
chamber. It does not account for changes in vapor pressure, but this

effect was minimized by maintaining saturated conditions in each chamber.

2
VBV -£1..:_22. V1_._2_73__ ()
2 92 273+AT

P1 - initial pressure of standard chamber

P2 - pressure of system with jars interconnected
V1 - volume of standard chamber

V2 - volume of subject chamber

st - temperature change in standard chamber

With this procedure, Liuzzo st 31. attempted to establish a relation-
ship between body density and composition, so that it could be used to
predict the total fat content of live guinea pigs. Two experiments were
conducted; in the first, density was correlated with total carcass fat,
water, protein, and ash with values of -0.70, 0.67, 0.68, and 0.56, re-
Spectively. 'In the second experiment, the correlation coefficients were
slightly higher, being -0.82, 0.81, 0.72, and 0.72, respectively. These
higher values were partially a result of using a greater absolute pressure
in the procedure for determining volume. They stated that this method was
‘much more rapid to execute than those reported by previous investigators.
He also stated that the contents of the elimentary tract did not signifi-

cantly alter the relationship between body density and composition.

-10-

In a previous experiment, Gnaedinger (14) determined the density of
26 male humans by air displacement and compared the values with under-
water weighing. A positive relationship (r a 0.361) existed between the
values obtained by the two methods, but a comparison to composition was
not possible, since neither method had been validated by direct compari-
son studies. The apparatus (Figure 1) and procedure were essentially
the same as that used by Liuzzo, with a few modifications. The subject
chamber was of 460 liters capacity and the standard chamber was 180
liters. Pressures less than atmOSpheric were used to measure volume.
Also, a different equation for computing body volume from the experimental

data was used and is given below. This equation accounts for changes in

 

Pg - VP - P; - VP (3)
T; T;
V0 3 V2 - V1
BP - VP - P15 - VP
T3 T5
V0 - volume of subject
V1 - volume of standard chamber
V2 - volume of subject chamber

Pg, T5 - pressure and temperature of standard chamber after
interconnection of the two chambers

Pg, T; - pressure and temperature of standard chamber before
interconnection or at initial vacuum

(PA, T;)- pressure and temperature of subject chamber after
interconnection of the two chambers

BP, T; - pressure and temperature of subject chamber before
interconnection or at barometric pressure

VP - vapor pressure of water at the respective temperature

and pressure

relative humidity and temperature in both chambers. However, in this
study, vapor pressure corrections were not made in the standard chamber,
since all the air before entering this chamber, was didefl.to a constant
level.

The individuals used in this study ranged in condition from obese

to very thin, and the values obtained for density were definitely related

—11‘

 

"IV

EVAC UA’I‘ ION CHAMBER

/

 

 

 

 

 

 

 

 

 

 

 

ANIMAL CHAMBER

 

 

 

 

A- HYGROHETER

B- THERMISTOR

C&D- 3-HAY VALVES

W— GLASS STOPCOCKS

G— U TUBE HERCURY HANOMETER AND RESERVOIR

Figure I. Diagrammatic drawing of the apparatus designed to

measure body volume by air displacement.

 

 

-12..

to their condition. The values for density of this group ranged from
1.045 to 1.167. The greatest difficulty of this procedure was the in-
ability to obtain precise measurements of volume from day to day.
Corrections for relative hunidity resulted in more precision, but the
sensitivity of the electric hygrometer was a limiting factor in obtain-
ing accurate values for relative humidity. Another factor influencing
overall accuracy was the uncertainty of getting a representative temper-
ature reading of the air inside each chamber, since the apparatus was
located in a place where the ambient temperature was considerably differ-
ent from body temperature.
Density Determination by Helium Dilution

Since many difficulties are inherent in the procedure for deter-
mining body density by air displacement, it was only natural that some
other procedure be tried. Consequently, the helium dilution technique
was developed. This technique can be considered as a modified air dis-
placement method. The principle involves mixing a fixed, known quantity
of heliun with an unknown volume of air, and a subsequent determination
of the resultant concentration of helium in the air. Thus, when part of
the air in a chamber of known size, is displaced by a solid object, the
helium concentration of the remaining air will increase in proportion to
the volume of air displaced. The increase in heliun concentration is
then used as the basis for calculating body volume.

Walser and Stein (15) were apparently the first to employ this prin-
ciple, and they used it to measure the body volume of 10 cats. They
introduced a known quantity of helium, by a vacuum procedure, into a

desiccator jar containing a cat. After allowing sufficient time for

-13-

the helium to equilibrate with the air inside the chamber and reSpiratory
passages of the animal, a sample was withdrawn and analyzed for helium
concentration in a Cambridge Analyzer. This analyzer detected helium by
the thermal conductivity principle. The volune of the animal was then
computed with equation 4. This equation does not account for changes in
Volume of - volume of _[volume of gas added r4)
animal empty chamber final cone. of added gas

temperature and relative humidity of the air inside the subject chamber,

 

but Walser allowed for thermal equilibrium before the gases were mixed.
Helium was used as the added gas, because of its inert nature, its negli-
gible solubility in water and tissue fluids, and also because it has a
high coefficient of thermal conductivity.

Perhaps the greatest contribution to the helium dilution technique
was made by Siri (16). He constructed an apparatus for measuring the
body volume of human beings. The principle was the same as that mentioned
above. The greatest improvements in this technique, however, were the
method of measuring helium concentration and the computation of body
volume. He constructed an electronic circuit, which possessed exceptional
current stability, to power the thermal conductivity cell. Consequently,
the signal from the cell, resulting from a change in the thenmal conduct-
ivity of the gas flowing through it, could be read with great accuracy
and reliability. This was important since the value of this signal was
the parameter that reflected body volume. The equation used to compute
volume included factors which compensated for changes in relative humidity
and temperature of all the gases involved. Siri also performed a detailed

estimation of errors for this procedure. This estimation established the

-14-

magnitude of error that could be tolerated in each detail of design in
order to measure volune with a standard deviation of i 0.1 liter.

With this apparatus, Siri was able to measure the volune of inert
objects for which the standard deviation from the mean was i 0.028 liter.
The density values that he subsequently determined on a heterogenous
group of men and women, ranging in weight from 55 to 97 kg., ranged from
0.990 to 1.076. Siri states that even due to the unassessable errors
inherent in measurements of biological subjects, the standard deviation
of a single measurement would appear to be no greater than i 0.21 liter.
Estimation of Total Body Fat Content from Live Body Density

Numerous investigators attempted to predict total fat content of
animals as a function of density from an equation that best fits the rela-
tionship between these two variables. Merales.ggflgl. (17) developed a
theoretical equation from experimental data, relating body fat and density
of eviscerated guinea pigs (equation 5).

% fat = 100 (5.135 _ 4.694) (5)
(density

Rathbun and Pace (18) subsequently tested this equation for goodness of
fit with experimental data that they obtained on body density and fat
content of eviscerated guinea pigs. Their data showed a slightly differ-
ent relationship (equation 6).

% fat = 100 (5.501 - 5.031) (6)
(density

Due to a slight discrepancy between whole body density and eviscer-
ated carcass density, Morales (17) derived a theoretical equation relating
fat content of the whole body to its density (equation 7).

% fat a 100 (5.362 - 4.880) (7)
(density

-15-

Likewise, Pitts (19) derived a slightly different equation from his exper-

imental data on guinea pigs (equation 8).

% fat - 100 (4.183 - 3.790) (8)
(density

Rathbun (18) also derived a provisional equation for the conversion
of human body density to the correSponding fat percentage (equation 9).
The derivation was done by employing the basic equations that Morales
used for guinea pigs. The data which served as limits for use in these
equations were the values for density of human fat, 0.918 (20) and density
of the fat-free human body, 1.10 (21).

% fat = 100 (5.548 - 5.044) (9)
(density

Messinger g£._1. (22) subsequently used equation 9 to compute body fat
and water of guinea pigs with considerable accuracy.

Kraybill et a1. (23) determined the density of eviscerated cattle by
water displacement, and from these data and the values for total fat con-

tent derived equations for estimating percent fat (equation 10) and percent

water (equation 11).

% fat = 100 (4.802 - 4.366) (10)
(density
% water = 100 (3.896 - 3.486) (11)
density)

The derivation of equation 11 was based on a mean value of 72.6% water
in the lean body mass.

Kraybill ggugl. (24) continued their work with swine. They found
that a close relationship..existed between the fat content of the evis-
cerated carcass and its density. Likewise, fat content and backfat thick-

ness were closely correlated. Consequently, these investigators established

a theoretical equation which could be used to predict fat content of the

~16-

whole body from the density of the eviscerated carcass (equation 12).

% body fat = 100 (5.405 - 4.914) (12)
(density

Likewise, an equation for predicting body water was derived (equation 13).

% body water = 100 (4.400 - 4.021) (13)
density)

Siri (25) made a study of 100 normal human subjects, ranging in age
from 20-80 years, to establish values and natural variations in fat,
water, and nonfat solids. Body water was determined by tritium dilution
and density by his helium dilution method described above. Body fat was
calculated with equation 14, in which the constants depend on the respect-
ive densities of water, fat and lean tissue solids. This study showed

fat 8 2.66 x volume - 0.78 x water - 1.9 x weight (14)
wide deviations in body composition from lean to fat persons and wide
variations in groups of subjects with identical densities or body water.
Siri states that the empirical formulas now used for fat estimation are
fairly correct for limited ranges in body composition, but are of little

value for individual subjects when more reliable values are desired.

EXPERIMENTAL PROCEDURE

Egperimental Animals

Twenty four market weight hogs were obtained from the Michigan State
University swine farm and used in this study. They ranged in live weight
from 181 to 220 pounds. The group was selected without regard to breed
or previous treatment so that various degrees of fatness were represented.
All animals were held on the same ration for at least one day in order to
standardize the contents of the digestive tract. TWenty four hours be-
fore making the volume measurement, all feed was removed, but water was
available at all times. The first 9 animals were injected intramuscularly
with 3 cc. of the tranquilizer, Sparine, (50 mg. per cc.) about one hour
prior to measurement. The purpose of the tranquilizer was to make the
animals lie quietly while in the chamber. The treatment did not appear
to greatly reduce the animal's restlessness; therefore, it was discontin-
ued.
Determination_9fyBody Density by Air Diaplacement

APPARATUS: The apparatus used to measure body volume by air dis-
placement is shown schematically in Figure II. The dimensions of the
animal chamber were approximately 75 x 125 cm., but the volume was reduced
to 460 liters by welding to the sides air tight baffles that spanned the
length of the chamber (Figure III). This arrangement reduced the width
of the chamber to 41 cm. The standard chamber had a capacity of approxi-
mately 180 liters. Each chamber could be sealed hermetically by bolting
the door against a flange containing a rubber gasket. The chambers could
be interconnected or each could be connected separately to the atmOSphere

with a 3-way valve (valve D). Each chamber contained: (a) a squirrel

-17-

-18-

-mc\ /

standard chamber

 

 

 

 

 

 

 

yvnl’V‘a
_ - ‘ .r ..
n . n. un llllllllll

 

...

 

u-IHIHIIIIIIIIIIIIIIHIHHv

 

 

 

 

 

 

 

 

' animal chamber i.

 

 

 

 

 

A - hygrometer

B - thermistor

C&D - 3-way valves

E - glass stepcock

F - mercury manometer, cistern type

Figure II. Schematic of apparatus designed to measure body
volume by air displacement

-19-

 

 

 

 

 

 

 

Figure 111. End view of Open animal chamber showing
location of baffles

-20-

cage fan (50 cfm.) for rapid circulation of the air, (b) a thermistor
for reading temperature, and (c) an electric hygrometer sensing element
for reading relative humidity. In the animal chamber, these components
were mounted at one end and protected with a metal guard.

The vacuum gauge was a cistern-type, rising-stem manometer. This
type was chosen over the U-tube, because the total excursion of the mer-
cury due to a given pressure change was observed along one scale instead
of being divided equally on two scales. Also, by having the volume of
the cistern relatively large compared to the volume of the stem, a unit
change of mercury level in the stem would result in a negligible change
of the level in the cistern. Consequently, the maximum percentage error
resulting from uncertainties in pressure readings were reduced with this
type of gauge. The manometer was mounted permanently on the apparatus
and the scale was calibrated to read directly in absolute pressure, using
740 mm. of mercury asvbarometric pressure.

PROCEDURE: The procedure for measuring body volume was as follows:
The animal was placed in the chamber facing the door in order to avoid
the direct effects of expired air upon the thermistor and hygrometer
sensing elements. The door was then henmetically sealed, but the air
inside the chamber was allowed toequilibrate with the atmosphere until
the chambers were interconnected. A vacuum was drawn on the standard
chamber down to an absolute pressure of about 345 mm. of mercury, after
which a short time was allowed for temperature equilibration. The press-
ure of the standard chamber (Pg) was then read simultaneously with its
temperature (r;) by closing stopcock E at the instant that the tempera-
ture was read. Closure of this stopcock held the mercury level at the

point where the corresponding temperature was read, since there was a

-21..

time delay between reading and recording the data. Immediately thereafter,
the barometric pressure (BP) and temperature of the animal chamber at
barometric pressure (T3), were recorded concurrently with interconnection
of the two chambers (valve D). The ambient barometric pressure was not
necessary in this case, and a value of 740 mm. was used in all the calcu-
lations. This was compatible with the pressure readings taken from the
manometer, since the manometer was calibrated with reference to 740 mm.
of mercury to read directly in absolute pressure. After connecting the
two chambers, about two minutes were allowed for pressure and temperature
to establish a reasonable equilibrium, then the animal chamber was dis-
connected from the standard chamber and connected again to the atmOSphere.
At this time, the following manipulations and recordings were made as
nearly simultaneously as possible: (a) temperature of animal chamber
(T5), (b) closure of stopcock E, (c) temperature of standard chamber (Tg),
(d) pressure of animal chamber (Pé) and standard chamber (Pg), which in
this case are equal. The relative humidity inside the chambers was not
recorded, since vapor pressure corrections were not included in the
equation for computing volume. It was observed that vapor pressure did
not change appreciably during the course of a run. Since the uncertainty
in sensing relative humidity was quite large (i 2% of full scale), it was
deemed best to delete it from the equation. The volume of the animal
(V0) was computed with equation 15.

lie-.133 (15)

V0 - V2 - V1 T; T;
Eli-Bi
T3 T5

V1 = volume of standard chamber
V2 - volume of empty animal chamber

-22-

When the factors compensating for vapor pressure changes are included,

equation 15 becomes:

 

Ps'-VP_,P§-VP (16)
v v v Té T;
o 2‘ lBP-VP_Pa'-VP

T3 T5

VP 8 vapor pressure of water at the corresponding temperature
and pressure

In this study, three measurements of body volume were made on each
animal according to the above procedure, and the average of the three
was taken as apparent volume. Density was then computed with equation
17: 4

density a weight/volume (17)
weight - live weight of animal immediately before
the volume measurement

Preliminary studies on measuring the volume of the empty animal
chamber showed quite large variations in the average values obtained from
day to day. Thus, each day prior to measuring the animal volume, a volume
measurement was made for the empty animal chamber. This served as a cor-
rection factor and minimized the day to day variation in measuring volumes.
Determination of Body Density by Helium Dilution

APPARATUS: The apparatus used to measure body volume in this study
was modeled after the method developed by Siri (16), for measurement of
human body volume. The various individual components were changed when
necessary in order to adapt the system to measurement of the body volume
of pigs. The chamber used to confine the animals was the same chamber
previously described for air displacement and is shown in Figures II and
III.

The helium metering system is shown schematically in Figure IV. The

helium chamber was a propane gas tank and had a capacity of about 22 liters.

Bowman wcauouoe 55.35 mo gauge—Lam .>H ouswum

alcoves. 5:00» I 93
nouns—once was v0.30 I u
03.» also I n
yea-«luau I d

 

.23-

 

 

 

humane .530:

 

-24-

Two l-inch threaded pipes were welded in the chamber and served as gas
inlets and outlets. A thermistor was mounted through the chamber Opening
and positioned in the center. An air tight seal was made around the
thermistor wires with Epoxy cement. The helium tank was mounted perma-
nently on the animal chamber with a 1-inch pipe and a Jenkins steam valve.
Another arrangement of stapcocks and pipe fittings served to: (a) evacu-
ate the chamber, (b) introduce heliun into the evacuated chamber, (c)
maintain the helium filled chamber at atmospheric pressure without intro-
ducing any air, and (d) inject the helium quantitatively into the animal
chamber without altering its pressure. An Eberbach air pump capable of
producing 30 psi, or 24 in. of mercury, and of moving 1.5 cubic feet of
air per minute was used to inject the helium into the animal chamber.

The pump was allowed to circulate the air-heliun mixture between the two
chambers throughout the duration of the measurement. Equilibrium between
the two gases was attained in about 4 minutes. A Cenco Hy-Vac vacuum
pump was used to evacuate the helium chamber. The gauge used to record
vacuum was a cloSed-end manometer.

The helium analyzer consisted of a thermal conductivity cell, a power
supply, and a potentiometer. .All these components are commercially avail-
able. The cell (Cow-Mac model 9737, 30-8) contained 8 tungsten, type
9225, resistance filaments mounted in a brass, Z-pass T/C cell. The power
supply produced a constant direct current to the cell and was a Gow-Mac
'model 9999-C-l:1 unit. The potentiometer for recording the signal from
the cell was a Sargent model SR recorder, 2.5 mv.

Since the signal from the 8 filament cell exceeded the range of the

recorder, an attenuating resistance circuit was wired to series between

-25...

the power supply and cell (Figure V). The circuit consisted of two re-
sistance decades wired in series to give a total resistance of 10 ohms
in 0.1 ohm steps. This circuit allowed for most of the signal to be
attenuated, leaving only the residual signal to be read on the recorder.
The attenuation was accomplished without reducing the sensitivity of the
instrunent or the residual signal. To determine the amount of signal
attenuated, the decades were calibrated with reference to the deflection
obtained on the recorder for a 0.1 ohm change in resistance. By multi-
plying the nunber of ohms required to attenuate the signal by the
defhection per ohm, the total signal attenuated was computed in terms of
arbitrary units of deflection. The total output signal was the sum of
the attenuated signal and the residual. In this study, the sensitivity
Of the power supply was adjusted so that 0.1 Ohm.gave a deflection of 65
units on a full scale of 100 units per 2.5 my.

The thermal conductivity cell was Operated at constant temperature
in a mineral Oil bath (Figure VI) that was maintained at a temperature
of 47 i 0.01°C. This value was chosen, since the regulation was best at
this temperature. The oil bath tank was made of plexiglas, with dimen-
sions 9 x 10 x 14 inches, and was insulated with 1 inch Styrofoam, A
plexiglas cover served as a support for suspending the cell in the oil.
The temperature of the bath was regulated with a thermistor-actuated
Sargent Thermonitor. Two heaters were used with this unit, one a knife
type heater of 250 watts, and the other a cycling 60 watt light bulb.
The stirrer for circulating the Oil was mounted firmly on a support that
was independent of the oil bath, so that the vibration would not affect

the cell. The power supply, thermonitor, and recorder were partially

-26-

 

 

constant current source

 

 

 

cosrst

current
control
fins

zero

control
10, 0.1 Ohm
fixed

resistance
(decades

 

”his“ I

 

cell

sensitivity

t . control

recorder I

 

 

 

 

 

Figure V. Schematic of helium analyser showing location
of resistance decades

 

 

 

 

 

.27-

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure VI.

A - styrofoam insulation, 1 inch
3 a thermistor thornorsgulstor
C - thenmistor

D - heater, 250 watts

E n heater, 60 watt light bulb

P - stirrer

Schematic of Oil bath and accessories

 

 

 

-23-

enclosed in a plywood cabinet, in which a 40 watt light bulb served as
a crude thermoregulator.

The gas sampling system for monitoring the reference and chamber
gases through the cell is shown schematically in Figure VII. The water
cans (5 gallon metal reagent containers) were interconnected at the
bottom, thereby forming a common drainage point. RUbber st0ppers and
tygon tubing were used to connect the cell to the cans, so that an air
tight, closed system was formed. Thus, as the water flowed out at the
bottom of the cans, air was drawn through both sides of the cell. Also,
since there was no resistance to the flow of gas in the system, the
water levels remained equal, thereby assuring an equal flow rate through
each side of the cell. The flow rate in this system ranged from about
800 to 400 cc. per minute as the water level in the cans decreased. The
reference gas, which was dry air in this case, was brought in from out-
side the building so that its composition.would not change during a run.
Calcium chloride was used to dry the reference and the chamber gases
before they entered the cell.

PROCEDURE: The procedure for measuring body volume was similar to
that used by Siri (16). Before the animal was put into the chamber,
adequate preparations were made so that the measurement could be per-
formed without interruption and as rapidly as possible. The helium
chamber was evacuated down to an absolute pressure of about 5 mm. of mer-
cury, filled with helium, and again evacuated to a pressure of about 1
mm. This procedure appeared to be adequate to remove all the air from
the chamber and to fill it with pure helium. The current to the cell was

then adjusted to approximately 110 mm. and the recorder was zeroed with

chamhar gas

water
absorber

.29.

l
1

[1E

 

ODD“

 

 

 

 

 

 

 

rafarsnca gas

watar
absorbar

 

 

 

 

 

Figure VII. Schematic of gas sampling system

-30..

the reference gas flowing through both sides of the cell. The outlet
from the air pump (Figure IV) was inserted through a hole in the animal
chamber, which was slightly larger than the outside diameter of the pump
outlet. This hole served to keep the air of the animal chamber in equili-
brium with atmOSpheric pressure. It also served as an air inlet while
the air-helium mixture of the chamber was being monitored through the
cell. The animal was then placed in the chamber and the door bolted
tight enough to prevent air leakage. Immediately thereafter, one side
of the cell was switched from the reference to the chamber gas, and a
deflection of the recorder needle was obtained which corresPonded to the
gasous exchanges due to respiration.

The system was now ready for the helium injection. The necessary
recordings and manipulations were made in the following order: (a)
temperature of the helium, (b) temperature and relative humidity of the
air in the animal chamber, (c) interconnection of the helium and animal
chambers with value B (Figure IV), (d) resistance value of the decade,
and (e) temperature of the oil bath. The curve on the recorder was also
marked at the exact time when the helium injection was started (manipu-
lation c). As the helium concentration of the gas in the chamber in-
creased, a corresponding positive deflection was obtained on the recorder.
However, as the deflection increased beyond the width of the chart, the
resistance on the decade was correspondingly increased until the signal
was again brought back on the chart. About 4 minutes were required for
the heliun-air mixture to reach equilibriun throughout the chamber and
the animal's respiratory passages. This point was determined simply by
observing the shape of the recorded signal, as an inflection point occurred

when equilibrium was reached (Figure VIII). The recording was continued

«Emu noduonuaouuoo Sim: dogma? a mo mudgup flung—050m

AmmSzEV any

 

.2 NH 0.— w o e
< 4‘ 4 . . . a u u 1‘ u 1 < —
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/ _

  
         

0:30
gausuucouaou Sufism \

osuao acuuuavOHQ Noe
.gaumgncoo No

-31-

unwed
.3221...»

«Reg
.3. I ma: guuaaoauuuxm .
R a 8 - no A: N /
32 n 3 AH... 1o - use «.3 /
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/
/

 

 

 

 

 

51011031130

-32-

for at least 6 minutes beyond the equilibrium point, during which time
the signal produced a curve of constant negative slope. The decade re-
sistance was adjusted so that the curve of negative slope extended the
full width of the paper. This curve was extrapolated to zero time, or
the time of heliun injection, at which point the heliun concentration in
the chamber was theoretically at a maximum. The deflection at this maxi-
mum was the value used to compute animal volume and is designated as R0
in equation 18.

The following equation was used to compute body volune:

Vo a VzRiRo-RD - V1R1(Ro-R2) + v(So-51)(R2-R1) - v (82-31) (Ro'R1~) (18)
R0012-411)

volume of animal

volume of reference 1 - 83.16 liters

volume of reference 2 - 103.56 liters

volume of helium chamber a 22.075 liters

observed deflection at zero time with animal in the

chamber

R1 a computed deflection :5 conditions of R0 and with refer-
ence to V1

R2 - computed deflection at conditions of R0 and with refer-
ence to V2

So 3 30/7

S1 = R1/7

$2 - R2/7

<
N
fllllll

The use of this equation required calibration of the apparatus between
two references of known volume. The volumes used are indicated above.
This range was sufficient to bracket the range of volumes of the animals
used in this study. A number of runs were made on each reference accord-
ing to the above procedure and a plot of deflection versus helium
concentration was made (Figure IX). Deflection values were obtained by
extrapolating the dilution curve of the recorded signal to zero time as
previously described. Helium concentration was computed with equation

19.

oofisao> oocvuomsu duos us acauouunoonoonaawfion nacho» ou=~s> aouuouauov we nacho .NH shaman

so. 238%:

onou odes Dang osmu onmm omna o
4 d d _ d — 4‘ d s d. d 1 — d 1 J‘ — d ‘—‘I d d 4

'6'5

  

mo.~hnwb

1mm +~ «£3 a x m
. 9m

1.0
o
0
,. N
3 3
A... - m
m
9m
1. I
1.0
N
i .nu
. n\

2'9

 

 

 

-34-

c - v (19)
(Vc - V1) 7 +'v

v - volume of helium chamber
Vc - volume of empty animal chamber
V1 - volume of reference being used

7'111(P-p) (20)
To ( P )

Th temperature of helium at time of mixing‘

Tc temperature of animal chamber at time of mixing

P = barometric pressure or 740 mm.
p - vapor pressure of water at Tc and P

The plot of deflection versus concentration was assumed to be linear
over the range of the reference volumes. Thus, a linear equation express-
ing this relationship between these two variables was computed (equation
21). From equations 19, 20, and 21, the values for R1, R2, 30, $1, 82,
and 7 were computed for use in equation 18.
R1 - 245.2 c1 + 89.1 (21)

Sampling and Analysis of Carcass

The experimental animals were weighed, immediately put in the cham-
ber, and measured for body volume. Helium dilution was run first followed
by air displacement, without removal of .the animals from the chamber.
About 30 minutes were required to complete both measurements. The animals
were killed by bleeding within one hour after completing the measurements.

The amount of blood was computed from the difference in weights
taken before and after bleeding and a sample of blood was collected for
chemical analysis. The carcass was then dressed according to conventional
procedures. The scurf, hair, and toenails were collected quantitatively.
The composite was air dried, ground twice in a meat grinder and sampled
for chemical analysis. The values for the composition of hair reported

herein, were obtained from a composite sample of the hair of six animals.

-35-

These hair samples were randomly selected, ground together, and analyzed
as one sample. The head was removed, leaving the jowls on the carcass,
and sealed in a plastic bag. The carcass was eviscerated over a container
which served to catch any body fluids and blood clots that remained in

the body cavities. The carcass was then split and chilled for 24 hours
prior to being frozen at -20°F. Length and backfat thickness (lst rib,
last rib, last lumbar vertebra) measurements were taken on the chilled
carcass.

The viscera wasedivided into 3 parts in order to determine the con-
tribution of each to the intact animal. The lungs, trachea, esOphagus,
heart, liver, Spleen, and kidneys were removed and sealed together in a
plastic bag. The intestines and stomach were emptied and along with the
caul fat composed the second part. The third part included the intestinal
contents, blood clots, and any remaining body fluids. .All parts were
weighed and then frozen at -20°F. Thus, each animal was dissected into
7 separate components for chemical analysis. This method of dissection
yielded no less than 99% recovery of the weight of the live animal.

To get a homogenous sample of the frozen components for chemical
analysis, the following procedure was used: Each component was cut into
strips about 1/8 in. in thickness and up to 3 in. in width with an electric
meat saw. The frozen strips were then ground 6 times, after which a
sample weighing approximately 70 gms. was taken for analysis. Five
plates, ranging in size from 1/2 in. to 1/8 in. were used. The sample
was ground twice through the 1/8 in. plate. A 1.5 HP, Enterprise, model
2632 electric meat grinder was used. 'With this procedure, the bones in
the carcass and head were sufficiently macerated and mixed with the meat

to yield a homogenous sample. The teeth and some small pieces of bone

-36-

caused a little difficulty, since some of the fragments were still too
large to go through the 1/8 in. plate. .Also, the teeth dulled the saw
blade very quickly.

After grinding, the samples were stored at -20°F until analyzed.
Each sample was analyzed for moisture, ether extract, protein, and ash.
The amount of moisture was determined according to the procedure of
Benne gt 31. (26) with two exceptions. The disposable aluminum foil
dishes used in this study were approximately 15 mm. deep and did not
have lids. Also, all samples were dried for 24 hours at‘a temperature
of 100 to 105°C. ‘

The amount of ether extract was determined on the dried samples left
from the water determination. The samples were extracted with the Gold-
fisch Extractor, which was described by Hall (27). The dried samples
were enveloped with the aluminum dishes in a cylindrical manner, leaving
both ends open so that the extractant would thoroughly penetrate the
samples. The dish and contents were then inserted into the extraction
thimble. The samples were extracted with anhydrous diethyl ether for 4
hours. The ether was distilled into a collecting vessel and subsequently
re-utilized. The taredeeakers were then removed from the extractor,
dried in an oven at loo-105°C fpr about one hour, cooled to room tempera-
ture in a desiccator, and reweighed. The amount of ether extract was
determined from the weight of the residue collected in the beaker after
extraction.

The detenmination of protein was perfonmed according to the Kjeldahl
procedure as outlined by Benne‘gtngl. (26).

Ash content was determined on samples weighing approximately 5 gms.

The empty crucibles (Coors, #3, porcelain) were heated for 10 minutes at

-37..

525°C, cooled to room temperature in a desiccator, and tared. The same
ples were weighed into the crucibles and dried in a hot air oven for at
least 12 hours. The dried samples were then ashed at 525°C for 24 hours.
The crucibles and residue were removed from the furnace, cooled to room

temperature in a desiccator, and reweighed to obtain the amount of ash.

RESULTS AND DISCUSSION

Relationships between Various Density Values

The results of the density determinations are summarized in Appendix
Table l. The values for air displacement ranged from 0.975 to 1.222 with
a mean value of 1.075. The range for helium dilution was slightly lower
with values of 0.940 to 1.114 and a mean value of 1.017. The values for
helium dilution for the first 10 animals were omitted, since the tech-
nique of measurement was not valid on these animals.

Theoretical density values were computed with the following equation
of Kraybill g; 31. (23):

G - M (22)
§L_+-MPF
Df I’1

whole body density
weight of whole body
weight of body fat

density of pork fat = 0.914 (20)
density of lean body mass - 1.1 (21)

30

D
D

l-H-h'fl

These values were computed in order to compare them with the densities
obtained by helium dilution and air displacement. The values can be
assumed to be reasonably correct, since they were determined directly from
chemical analysis data. The values ranged from 1.015 to 1.042 with a
mean of 1.0312.

The correlation coefficients between the 3 sets of density values
are given in Table I. The air displacement densities were correlated
inversely and nonsignificantly with both the helium dilution and the
theoretical densities. The helium dilution densities were correlated
directly but non-significantly with the theoretical values. Thus, the

correlation coefficients indicated that the helium dilution densities were

-38-

-39-

Table I. Summagz of correlation coefficients

 

 

 

Density
Variable Air Helium

displacement dilution Theoretical
Air displacement density ------ -0.126 -0.021
Helium dilution density ------------ 0.134
Z carcass moisture -0.056 0.239 0.918**
Z carcass protein -0.113 0.209 0.825**
Z carcass ether extract 0.001 -0.176 -0.931**
Z carcass ash -0.362* -0.145 0.417*
Z ether extract of whole body -0.008 -0.216 -0.944**
Z ether extract of empty body -0.016 -0.200 -0.935**
Backfat thickness 0.326 0.082 -0.546**
Z ether extract: empty body vs carcass 0.99l**
Z ether extract of carcass vs backfat thickness 0.690**
Z ether extract of empty body vs backfat thickness 0.667**

Z moisture of empty body vs Z ether extract of body@w#7)-0.974**
Z moisture of whole body vs Z ether extract of

whole body -0.976**
Z moisture of whole body vs Z ether extract of
empty body -0.971**

Z moisture of ether extract-free, empty body vs Z ether

extract of empty body -0.579**
Z protein:ether extract-free, empty body vs ether

extract-free, carcass 0.862**
Z moisture: ether extract-free, empty body vs ether

extract-free, carcass 0.86$**
Z ash: ether extract-free, empty body vs ether

extract-free, carcass 0.867**
Z carcass protein vs backfat thickness -0.599**
Z carcass protein vs length 0.180
Z carcass ether extract vs length 0.245

 

** Significance at the 1% level
* Significance at the 5Z level

-40-

somewhat more predictive of body composition than the air displacement
densities. Table I also includes correlation coefficients for carcass
and body composition with the density values obtained by the various
methods. The correlation for the densities detenmined by air displace-
ment with both Z carcass protein and Z carcass water should theoretically
show a positive instead of a negative relationship. Likewise, the values
for Z ether extract in the carcass and backfat thickness should be in-
versely related to density, but were both positive. The values under
helium dilution are higher than those under air diSplacement, but all are
statistically non-significant. The correlation coefficients discussed
above indicated that the helium dilution technique of measuring volume
was slightly superior to the air displacement method.
Errors in Measuring Density By Air Displacement

As was previously mentioned in the procedure, the greatest diffi-
culty encountered with the air diaplacement method was its lack of pre-
cision in.measuring volumes from day to day. In an attempt to correct
for this variation, the volume of the empty animal chamber (an average
of 3 determinations) was made each day, prior to measuring the volune of
the experimental animals. These data were analyzed statistically in
order to ascertain the magnitude of the variation. The values obtained
for the volume of the empty chamber ranged from 454.71 to 470.83 liters,
with a mean of 464.61 and standard deviation of i 4.7 liters. An analy—
sis of variance of the data is given below. The analysis showed that
there was a significant difference between the means obtained from day
to day. There was alsoasignificant difference between the 3 samples

that composed each mean.

-41-

Table II. Analysis of variance of values obtained for the volume of the
empty animal chamber

 

Source of variation Degrees of freedom Mean square F ratio
Total 38 ----- ---
Between means 12 66.42 110.7**
‘Within means 2 3.57 5.95**
Error 24 0.60 ---

 

An estimation of errors was performed on equation (16) in order to
ascertain the source of the variation that consistently occurred in com-
puting volumes. For this estimation, the following limits were estab-
lished: (l) the maximum error in reading pressure was i 0.1 mm. on each
limb of a U-tube mercury manometer, (2) the maximum error in reading
temperature was i 0.l°C, (3) the maximum error in reading relative humid-
ity was lZ (the accuracy of the electric hygrometer was i 2Z of full
scale), (4) the air in the standard chamber was kept dry so that relative
humidity corrections were not required in this chamber. Under these
conditions, the maximum percentage error in computing a gas volume of
445.43 liters was 2.54Z. A maximum percentage error was also computed
using equation 15 in order to ascertain the effect of relative humidity
on the total error. The limits on this equation were the same as above,
with the exclusion of the relative humidity corrections. The maximum
error was reduced to 0.79Z. Thus, it appeared that relative humidity
was a potential source of large error.

In this study, a cistern-type manometer instead of a U-tube was

used to read pressure. An estimation of errors was computed with this

-42-

type of manometer using equation 15 in order to see its effect on the
total error. The value thus obtained for the maximum percentage error
was 0.72Z. This was a slight reduction over using the U-tube, primarily
because readings are taken from only one limb with a cistern-type mano-
meter.

The above estimation assunes that all the errors are additive, but
this does not usually happen in actual practice. However, other sources
of error which are inherent in.measuring live animals are likely to occur
and contribute even more to the overall error. For instance, the magni-
tude of the error resulting from a non-representative temperature reading
in the chambers was difficult to ascertain. Since the temperature of
each chamber was recorded with a single thermistor, it seems likely that
errors as great as i 0.5°C were possible. Furthermore, uncertainties in
temperature readings undoubtedly increased as the ratio of body tempera-
ture to room temperature increased.

The estimation showed that uncertainties in reading relative humidity
contributed greatly to the overall error. Furthermore, the accuracy in
reading this variable was limited to the accuracy of the electric hygro-
meter. In view of this, it would appear desirable to delete vapor press-
ure corrections from the equation used to compute volume. This could be
done provided the relative hunidity of the air in the chambers was main-
tained at a constant level of saturation, at least during the duration
of a run. However, the assunption of a constant level of saturation may
not be valid, since relative humidity is quite sensitive to temperature
changes. Also, vapor pressure is affected slightly by barometric press-

ure according to the Carrier equation, (equation 23).

-43-

PH " wa' (am) (23)

tdb, twb - temperature of dry bulb and wet bulb, reSpectively
PH - partial pressure of water vapor

wa I saturation pressure of water vapor at twb
p - barometric pressure

Since pressure and temperature changes occurred in both chambers, it ap-
peared likely that the assumption of a constant level of saturation
introduced a considerable error in computing volumes.
Errors in MeasuriggiDensity by Helium Dilution

A detailed estimation of errors involved in the instrumental design
of the helium dilution method was given by Siri (16). He defined the
limits in which each variable must be controlled in order to measure
volume within a standard deviation of i 0.1 liter; fifith the apparatus
used in the current study, the volume of an inert object was determined
with a mean deviation of 0.81 liter for 8 determinations. Most of this
variation appeared to be a function of current adjustment. The power
supply was highly stable at any particular current setting. However,
the precision with which current could be adjusted from day to day ap-
peared to be the major cause of deviation. The degree of precision was
in turn limited by the accuracy with which current could be set on the
milliammeter. The meter on the power supply could not be adjusted more
accurately than i 0.1 ma. Ideally, current adjustment should be made
with a precision of at least i 0.01 ma. Thus, the greatest source of
error in measuring the volume of inert objects appeared to be adjustment
of the current.

The equations and method for computing volume by helium dilution
assume that all variables remain constant or that they change at a con-

stant rate throughout the duration of a run. However, the variables did

not change at a constant rate, since the animals displayed various degrees
of activity while in the chamber. The effect of these variables on the
concentration of helium passing through the cell can be seen by inspection
of equations 19 and 20. As the relative hunidity of the air in the
chamber increased, 7 decreased; thus concentration increased. Likewise,
as the temperature of the animal chamber increased, so did the concentra-
tion of helium. Thus, the effect of temperature and humidity on heliun
concentration was additive. It is conceivable that these variables may
have changed at a more rapid rate immediately after putting the animal
in the chamber than at the end of the run. Consequently, the lepe of
the helium concentration curve would be different at the beginning of a
run than at the end. Any change in the lepe of this curve introduced
uncertainties into its accurate extrapolation to zero time (Figure VIII).

The magnitude of the errors caused by changes in temperature and
relative humidity can be approximated by inspection of Figure IX. The
points at the bottom of the graph were obtained on measurements of refer-
ence 1. Likewise, the points at the top were obtained on measurements of
reference 2. The diapersion of these points was due to changes in temper-
ature and relative humidity of the air in the animal chamber. The
temperature of the helium at the time of injection also affected the
final concentration of heliun in the animal chamber. However, subsequent
changes in the temperature of the helium chamber had no appreciable effect
on the final concentration.

In order to remove the effects of changes in temperature and rela-
tive humidity, they will necessarily have to be maintained constant or

controlled to change at a constant rate throughout the duration of a

-45-

measurement. The effect of relative humidity could be minimized by main-
taining the air of the animal chamber in a saturated condition. Saturation
of the animal chamber can be accomplished most conveniently by wetting
the skin of the animal with water prior to putting it in the chamber.
Temperature changes are more difficult to control. The thermal expansion
of the air-helium mixture in the chamber is a probable source of error.
If expansion of the gas mixture exceeded the rate at which it was being
minitored through the cell, some of the helium would be forced out of the
chamber. For instance, a temperature increase of 0.5°C per minute would
expand the gas at a rate of about 1 liter per minute, yet the flow rate
of the gas sampling system did not exceed 500 ml. per minute. In this
study, the temperature of the chamber was considerably lower than the
body temperature of the animal. Temperature differences up to 10°C were
commonly observed. Thus, it appeared likely that the thermal expansion
of the air-helium mixture was a possible source of error. The thermal
expansion of the mixture could be somewhat minimized by maintaining the
temperature of the animal chamber somewhere near body temperature.

The greatest source of error in measuring body volume appeared to be
due to the activity of the animals inside the chamber. iMost of the ani-
mals became excited when enclosed in the chamber. Some fought continu-
ously and to the point of exhaustion in an attempt to escape from the
chamber. Others were less excited and fought only intermittently. Thus,
the degree of excitement affected the rate of respiration and consequently
the rate of heat and moisture accumulation in the chamber. These changes
in temperature and humidity were reflected in the slope of the helium
concentration curve. The gaseous exchange due to respiration was impor-

tant, since the cell was responsive to all the gases that passed through

-46-

it. The accumulation of carbon dioxide and depletion of oxygen effected
a change in thermal conductivity in a direction opposite to that of helium.
Thus, this effect was superimposed on the helium concentration curve.

The method of correcting for the gaseous exchanges consisted of extrapo-
lating the helium curve to zero time (time of known respiratory gas
composition). The accuracy of this correction in turn depended upon a
straight line for the slope of the curve that represented the changes in
these gases (Figure VIII). Since the activity of the animals was not
constant during a run, the slope of the curve was affected in proportion
to the degree of activity. Consequently, the slope was not constant and
an accurate extrapolation to zero time was virtually impossible. An
attempt was made to minimize the accumulation of carbon dioxide in the
chamber by absorbing it with Ascarite. A tray of absorbent was placed
inside the chamber so that it would absorb the carbon dioxide as the air
was circulated around it. This procedure resulted in greater variation
in the slope of the curve than when no absorbent was used. This appeared
to be due to the degree of activity of the animal. When the animal was
restless, its carbon dioxide production apparently exceeded the rate at
which it was absorbed by the Ascarite. The opposite appeared to occur
when the animal lay quiet.

The carbon dioxide content of the air in the chamber affected the
helium concentration in the same manner as did water vapor. Both gases
served as diluents for the helium. Thus, if either or both gases are
removed from the air-helium mixture, the resultant helium concentration
passing through the thermal conductivity cell will be affected propor-

tionally. An appropriate correction can be made for the quantitative

-47-

removal of water vapor from a knowledge of relative humidity (equation
20). However, the equation contains no factor to compensate for the
removal of carbon dioxide. Consequently, the absorption of carbon
dioxide was not valid, since the quantity removed could not be ascer-
tained. A carbon dioxide absorbent was used in the procedure for deter-
mining the volume of the first 10 animals in this study. Thus, their
values for density were omitted, since the results were not valid.

Another possible source of error was the loss of helium from the
chamber due to the rapid respiration of an excited animal. It was ob-
served that some gas (air-helium.mixture) was forced out of the chamber
with each expiration of the animal. An equal amount of gas (air only)
was in turn drawn into the chamber with each inspiration. Thus, the
helium concentration of the chamber was being constantly reduced. A
correction for this loss can again be effectively performed by extrapo-
lation of helium concentration curve. However, an error would result if
the loss of helium did not occur at a constant rate. Any variation in
the rate of dilution would cause the slope of the helium curve to changeu
and an accurate extrapolation would be impossible.

Results indicated that the activity of the animals must necessarily
be controlled before accurate results can be expected. It is recommended
that volume measurements be attempted on anesthesized animals. This
would tend to prevent radical changes of the variables resulting from
changes in the respiration rate of excited animals. It is also recommended
that the animal be moistened with water in order to maintain saturated
conditions of the air in the chamber. Also, the temperature of the cham-
ber should be maintained close to body temperature in order to minimize

the errors due to the thermal expansion of the air-helium mixture.

-43-

Bodngquosition Relationships

The moisture content of the dressed carcasses ranged from 38.31 to
49.50Z with a mean of 45.81Z. The moisture content of the empty bodies
(the entire live animal minus the contents of the G.I. tract) ranged from
41.73 to 52.54Z with a mean of 48.49Z (Appendix Table 12). Mitchell and
Hamilton (28), working with pigs, reported mean values of 41.41 and 47.92Z
for the moisture content of the dressed carcasses and empty bodies, re-
Spectively. Their data were obtained from animals representing the chuffy,
intermediate, and rangy types and were slaughtered at 175 and 225 lbs.

The ether extract content of the dressed carcasses ranged from 31.89
to 46.84Z with a mean of 37.45Z. The ether extract content of the empty
bodies ranged from 27.97 to 41.50Z with a mean of 33.50% (Appendix Table
12). iMitchell and Hamilton (28) reported mean values of 43.13 and 37.07Z
for the fat content of the dressed carcasses and empty bodies, respectively.
Thus, the pigs used in their study contained about 5Z more fat in the
dressed carcasses and about 3.5Z more fat in the empty bodies.

The protein content of the dressed carcasses ranged from 11.90 to
14.32Z with a mean of 13.19Z. The protein content of the empty bodies
ranged from 12.54 to 14.77Z with a mean of 13.78Z (Appendix Table 12).
Mitchell and Hamilton (28) reported mean values of 12.14 and 12.04Z for
the protein content of the dressed carcasses and empty bodies, respectively.
Thus, the pigs used in the current investigation had about lZ more protein
in the carcasses and about 1.7Z more protein in the empty bodies than
those used by Mitchell and Hamilton.

The ash content of the dressed carcasses ranged from 1.99 to 3.18%

with a mean of 2.75Z. The ash content of the empty bodies ranged from

-49-

2.20 to 3.15Z with a mean of 2:14Z (Appendix Table 12). Mitchell and
Hamilton's data (28) showed mean values of 2.76 and 2.42Z for the ash
content of the dressed carcasses and the empty bodies, respectively. The
composition of Mitchell and Hamilton's group of animals was slightly dif-
ferent from the group used in this study, with the exception of ash con-
tent. Some of the differences in composition of the carcasses may have
been due to the fact that the head was apparently included in their car-
cass analysis. Also, their group of animals was fatter than the group
used in this study.

The average weight of the air dried hair (including scurf and toe-
nails) was l.l lbs. for the group of animals used in this study (Appendix
Table 2). This value was slightly higher than the 0.7 lb. obtained for
these components reported by Mitchell and Hamilton (28) on pigs weighing
225 lbs. These authors obtained values of 6.81, 2.49, 87.0, and 5.64Z
for the moisture, fat, protein, and ash content, respectively, of the air
dried hair. The values obtained in this study were 8.25, 1.91, 89.0, and
1.31Z for moisture, ether extract, protein, and ash, reSpectively (Appen-
dix Tables 3 through 6). Thus, the moisture content of the hair was about
1.5Z lower in Mitchell and Hamilton's group of animals. This difference
may have been due to the degree of air drying of the material. The values
for fat and protein agreed favorably between the two groups of animals.
The ash content of the hair was about 4% lower for the animals used in
the current study.

The composition of blood for the group of animals used in this study
was 79.75, 0.1, 18.95, and 1.22% for moisture, ether extract, protein,
and ash, reSpectively, (Appendix Tables 3 through 6). IMitchell and Hamil-

ton (28) reported values of 80.20, 0.04, 18.6, and 1.22Z for moisture,

-50-

ether extract, protein, and ash, reSpectively. Thus, the composition of
blood for the two groups of animals agreed favorably.

A summary of the means and standard errors for the contribution of
each component to the whole animal (Appendix Tables 7 through 10) are
shown in Table III. The values indicate the maximun percentage errors
resulting from the exclusion of any one component or any combination of
components from the analysis of the total animal. The choice of either
excluding or including the analysis of any component will depend upon the
degree of accuracy desired in the total analysis. However, the use of
average values would reduce the maximum errors shown in Table 111, without
having to completely analyze the various minor components. This would be
desirable from a practical standpoint, since only the weights of the com-

ponents would need to be recorded.

Table III. Contribution of each component to the whole animal as percent-
ages of total moisture, ether extract, protein, and ash.

 

 

 

 

 

Moisture Ether extract Protein Ash

Mean S.D. Mean S.D. Mean S.D. ‘Mean S.D.
Carcass 74.08 1.80 89.79 1.44 76.13 1.30 79.11 3.53
Intestines* 5.99 0.68 5.07 0.94 3.95 0.41 1.63 0.31
Viscera** 5.87 0.40 0.95 0.18 4.55 0.25 1.68 0.18
G.I. contents 2.82 0.68 0.19 0.08 0.95 0.29 1.34 0.35
Head tongue 5.38 0.54 3.86 0.78 5.59 0.47 14.39 3.49
Blood 6.13 0.89 0.01 .005 5.19 0.87 1.68 0.33
Hair*** 0.09 0.02 0.03 .007 3.63 0.55 0.27 0.06

 

* Includes the intestines, stomach, and caul fat.

** Includes the liver, lungs, heart, kidneys, Spleen, esophagus, and
trachea.

***Includes scurf and toenails.

The carcass contributed 74.08Z of the moisture, 89.79Z of the ether

extract, 76.13Z of the protein, and 79.11Z of the ash to the composition

-51-

of the whole animal. Thus, the carcass had the greatest influence on

the composition of the live animal. The viscera, contents of the G.I.
tract, blood, and hair contributed negligibly to the total ether extract
content of the whole animal. The intestines, viscera, contents of the
G.I. tract, and blood each contributed about the same amount to the total
ash content in the whole animal (about 1.5Z). The data also showed that
the carcass and head combined, contributed 93.5Z of the total ash content
of the animal. The carcass, intestines, and head contributed a total of
98.72Z to the total ether extract for this group of animals.

The data suggest that the moisture, ether extract, and ash content
of the hair could be excluded from the total analysis without introducing
much error. However, average values could be used for percent moisture,
ether extract, and ash of the hair to further minimize the percentage
errors shown in Table III. The protein of hair contributed appreciably
to the total protein (3.63Z), but an average value could also be used for
percent protein since it is the major constituent of hair, scurf, and
toenails. Analysis of the blood for ether extract could be disregarded,
since it contributed only 0.011Z to the total ether extract of the whole
animal. The average weight of the contents of the G.I. tract was 3.44
lbs. for this group of animals. Thus, the percentage errors indicated
that average values could also be used for percent moisture, ether extract,
protein, and ash without introducing an appreciable error. However, this
‘may not be valid if the G.I. contents constituted a greater part of the
live weight.

The data showing the various relationships between the carcasses and
the whole bodies are given in Appendix Tables 11 through 13. The corre-

lation coefficients between the various carcass and body parameters are

-52-

given in Table I. The percent ether extract of the carcass was correlated
significantly with that of the empty body (r = 0.991). The following re-
gression equation for estimating percent body ether extract from the
percent ether extract of the carcass was derived from the experimental
data:

9 - 0.881X + 0.489, Sx-y =- i 0.9437. (24)
This relationship indicated that the ether extract of the carcass can be
used as a reliable means for estimating the ether extract content of the
body. For instance, if the ether extract content of the carcass were in
error by i lZ, the resulting error for the ether extract content of the
body would be about i 0.88Z. The standard error of regression for equa-
tion 24 is indicative of this accuracy. From a practical standpoint,
equation 24 implies that an accurate estimate of body ether extract can
be obtained from an analysis of the carcass only. However, it is possible
that this relationship may not be applicable to animals of a different
weight gauge.

Harrington (29) recently reviewed the methods of estimating total
body fat from measurements of total body water. .A knowledge of total
body water can be used to estimate total body fat with considerable accur-
acy. From the experimental data obtained in this study, the following
regression equation was derived for estimating the percent ether extract
of the empty body from total body water.

3? - 97.16 - 1.298): (25)
Sx-y - i 0.52Z
rxy - -0.971
This relationship shows that the degree of accuracy for predicting total
body fat is about equal to the degree of accuracy of measuring body water.

For instance, a lZ error in.measuring body water will result in a 1.3Z

-53-

error in estimating body fat.

Clawson st 31. (30) analyzed the data of previous workers on the
chemical composition of the whole empty bodies of 127 pigs ranging in
weight from 10 to 350 lbs. and in age from 26 to 300 days. An examina-
tion of the data revealed that the percentages of water and fat are
highly and inversely correlated (r - -0.98). The data showed a curvi-
linear relationship according to the following equation:

9 - 178.83 - 0.63x - 66.62 logX , sx. - i 1.4%

X = percent water in whole empty bodyy
From the experimental data obtained in this study, the relationship be-
tween the percentages of water and fat in the empty bodies was computed
according to equation 26.

f - 96.40 - 1.297X (26)

sx-y - i 1.5Z

rxy - -0.974
A linear relationship was found, since this group of animals was rela-
tively homogenous with respect to age and weight. However, the correla-
tion coefficient obtained between the percentages of fat and water in
the empty bodies agreed favorably with that reported by Clawson 55 £1.
(30). Likewise, the standard errors of estimate agreed favorably.

Keys: and Brozek (31) and Harrington (29) have reviewed the dilution
technique of estimating total body fat from the percent water of the fat-
free body. The validity of this technique depends upon a non-significant
relationship between total body fat and percent water of the fat-free
body. The assumption is that the percent water of the chemically mature
body is constant, when expressed on a fat-free basis. From the data of

Pace and Rathbun (32) on 32 male guinea pigs, Keys and Brozek (31) com-

puted a correlation coefficient of 0.450 between total body fat and percent

-54-

water in the fat-free body. Kirton and Barton (33) obtained non-signifi-
cant, positive relationships between percent water of the fat-free carcass
and percent carcass fat of ewes. From the experimental data obtained in
the current study, the following equation was derived for predicting
percent ether extract of the empty body from the percent water of the

ether extract-free, empty body.

9 - 306.26 - 3.66X (27)
Sx-y - i 2.92%
rxy I -0.579

The correlation coefficient indicated that the water content of the fat-
free, empty body was not independent of ether extract content of the body.
The significance of this relationship suggested that the animals used in
this study were not chemically mature. This is in agreement with the
work of Moulton (34). He stated that the age at which swine attain chem-
ical maturity is between 6 and 12 months. Thus, the validity of estimat-
ing body fat from the water content of the fat-free body would be quest-
ionable for this group of animals. Also, the magnitude of the standard
error would limit the accuracy of predicting body fat from body water.
The results obtained by Clawson 35 El. (30) on the chemical analysis of
pigs weighing 225 lbs., showed an inverse relationship between the fat
content of the whole body and the water content of the fat-free body.
Thus, their work supports the results obtained in the current study.

The percentages of moisture, protein, and ash of the fat-free body
and of the fat-free carcass were computed to determine the constancy of
the values for this gram of animals. The results are sunmarized in

Table IV.

-55-

Table IV. Percentages of moisture, protein, and ash in the fat-free body
and fat-free carcass

 

 

 

Fat-free empty body Fat-free carcass
Moisture Protein Ash Moisture Protein Ash
Mean 74.51 21.26 4.23 74.17 24.41 4.46
Standard error 0.550 0.481 0.302 0.667 0.533 0.396
Mean* 76.18 19.1 3.84

 

*From Mitchell and Hamilton (28).

The means for percent moisture and percent protein between the body
and the carcass were not significantly different. The means for percent
ash were significantly different at the 5Z level. This significance may
have been due to the low ash content of the components other than the
carcass and head, since they each contributed about 1.5Zito the total ash
content of the whole animal (Table III). The relationship between the
values for percent moisture of the fat-free empty bodies and the fat-free
carcasses was highly significant (r = 0.951). Likewise, the relationships,
with respect to protein and ash, were highly significant (r = 0.881 for
protein and r = 0.867 for ash). The data of Mitchell and Hamilton (28)
in Table IV, showed that the moisture content in the fat-free bodies was
about 2Z higher than the moisture content of the animals used in the
current study. iMitchell and Hamilton (28) concluded from their study
that the composition of the carcasses was not much different from the
composition of the empty bodies. The results of the current study also
suggest that the composition of the fat-free carcass can be used to
accurately estimate the composition of fat-free body.

The estimation of live animal body composition from carcass composi-

tion is of limited value. From a practical standpoint, the composition

-56-

of the carcass is the most important economically. Yet, there is little
advantage in predicting the composition of the live animal from the car-
cass, since the animal has already been sacrificed and is no longer
available for further experimentation or breeding purposes. Since the
composition of the carcass and body is closely related, the most practi-
cal way of estimating carcass composition would be from body composition.
Thus, from this standpoint, an accurate indirect measure of live body
composition would be of great value. The density of a live animal would
be such a measure. If the density of an animal could be determined
accurately, it could then be used to predict the composition of a live

animal and in turn of the dressed carcass.

SUMMARY

The densities obtained on 24 market weight pigs by air displacement
were correlated non-significantly with the densities obtained by helium
dilution. The densities obtained by each method were correlated non-
significantly with percent moisture, ether extract, protein, and ash of
the dressed carcasses. Although neither method of measuring body volume
was reliable, the heliun dilution technique was more closely related to
actual body composition than the air displacement technique.

An estimation of errors for the air diSplacement technique was per-
formed. The greatest source of error appeared to result from inaccura-
cies in reading relative humidity. Other appreciable sources of error
were the uncertainties with which temperature and pressure could be read.

The major difficulties involved in the helium dilution technique
were caused by the activity of the experimental animals inside the cham-
ber. The changes in temperature, relative humidity, and the composition
of the respiratory gases were the major sources of error.

A chemical analysis of each animal was performed, and the contribu-
tion of each component to the composition of the whole animal was presented.
Data are presented which show the magnitude of errors resulting from the
exclusion of any body compartment, such as blood, hair,or head from the
chemical analysis of thevhole animal. The data suggested that average
values could be used for the composition of many of the minor components
without appreciably altering the composition of the total animal.

A regression equation was derived relating the percentages of ether
extract in the whole animals and the dressed carcasses. The equation
showed that body fat could be estimated from carcass fat with a standard

-57-

-58-

error of i 0.943Z. Also, a lZ error in carcass fat would result in an
error of 0.88Z in body fat.

A regression equation for estimating the percent ether extract of
the empty bodies from total body water was also presented. The regression
coefficient for the relationship was 1.29 and the standard error was
i 0.527..

A regression equation expressing the relationship between the fat
content of the empty bodies and the water content of the fat-free empty
bodies was computed. A statistically significant relationship was found
(r - -0.579). A 1% error in estimating the water content of the fat-free
empty bodies resulted in an error of 3.66Z for the fat content of the
empty bodies. Thus, the validity of estimating body fat from the water

content of the fat-free bodies would be questionable for market weight

pigs.

10.

11.

12.

13.

14.

LITERATURE CITED

Sears, F. W., and M. W. Zemansky. 1957. University Physics. 2nd ed.
AddisonAWesley Publishing Co., Inc., Reading, Mass. pp 210-219.

Spivak, 0. D. 1915. The Specific Gravity of the Human Body. Archiv.
Int. Med. 15:628-642.

wedgwood, R. J., J. R. Breckenridge and R. W. Newman. 1953. Measure-
ment of body volume by air disPlacement. Fed. Proc. 12:151.

Pfaundler, M. 1961. Korpermass-Studien an Kinder. IV. Vom Korper-
volumen und der Korperdichte. Ztschr. f. Kinderheilk. 14:123.

‘Murlin, J. and B. R. Hoobler. 1913. The energy metabolism of normal
and Marasmic children with special reference to the specific gravity
of the child's body. Proc. Soc. Exper. Biol. Med. 11:115-116.

Pfleiderer, H. 1929. ‘Methodik der Bestimmung dis spezifischen
Gewichts am Libenden (AntropOpyknometrie). Klin. WSchr. 49:2191-
2193.

Kohlrausch, W. 1929. Methodik zur quantitativen Bestimmung der
Korperstoffe in vivo. ArbeitSphysiol. 2:23-45.

Kohlrausch, W. 1929. Zur Kenntnis deS Trainingszustandes. Arbeits-
physiol. 2:46-60.

Bohnenkanp, H. and J. Schmah. 1931. Untersuchungen zu den Grundlagen
des Energie-und Stoffwechsells. IV. Mitteilung. Das Reinvolumen
sowie die spezifische Dichte des Menchen und die Bestimmungsweise
dieser Grossen. Pfluger's Archiv. 228:100-124.

Noyons, A. K. M. and J. Jongbloed. 1935. Uber die Bestimmung deS
wahren Volumens and deS spezifischen Gewichtes von Mench und Tier
mit Hilfe von Luftdruckveraanderung. Pfluger's Archiv. 235:588—596.

Jongbloed, J. and A. K. M. Noyons. 1938. Die Bestimmung des wahren
Volumens und des spezifischen Gewichtes von Menschen mittels Luftdruck-
veraanderung. Pfluger's Archiv. 240:197-201.

wedgwood, R. J. and R. W. Newman. 1953. Measurement of body fat by
air displacement. Amer. J. Phys. Antropol. 11:260.

Liuzzo, J. A., E. P. Reineke and A. M. Pearson. 1958. An air dis-
placement method for determining specific gravity. J. Ani. Sci.
17: 513-520o

Gnaedinger, R. H. 1960. Comparison of air and water diSplacement for
‘measuring the Specific gravity of the human body. IM.S. Thesis.
Nuchigan State University.

-59-

15.

16.

17.

18.

19.

20.

21.

22.

23.

24.

25.

26.

27.

28.

.. 60-

‘Walser, M. and S. N. Stein. 1953. Determination of Specific gravity
of intact animals by helium: comparison with water diSplacement.
Proc. Soc. Expt. Biol. Med. 82:774-777.

Siri, W. E. 1955. Apparatus for Measuring Human Body Volume. Rev.
Sci. Instr. 27:729-738.

Mbrales,'M. F., E. N. Rathbun, R. E. Smith and N. Pace. 1945. Stu-
dies on body composition. 11. Theoretical considerations regarding
the major body tissue components, with suggestions for application
to men. J. Biol. Chem. 158:677-684.

Rathbun, E. N., and N. Pace. 1945. Studies on body composition. 1.
The determination of total body fat by means of the body Specific
gravity. J. Biol. Chem. 158:667-676.

Pitts, G. C. 1956. Body fat accumulation in the guinea pig. Amer.

Hodgman, C. D. 1958. Handbook of Chemistry and Physics. 39th ed.
Chemical Rubber Publishing Co. Cleveland, Ohio. p. 1404.

Behnke, A. R. Jr., B. G. Feen, and W. C. welham. 1942. The Specific
gravity of healthy men. J. Amer. Med. Assoc. 118:495-498.

Messinger, W. J. and J. M. Stelle. 1949. Relationship of body Speci-
fic gravity to body fat and water content. Proc. Expt. Biol. Med.
70:316-318.

Kraybill, H. F., H. I. Bitter and 0. G. Hankins. 1952. Body composi-
tion of cattle. 11. Determination of fat and water content from
measurement of body Specific gravity. J. Applied Physiol. 4:575-
583.

Kraybill, H. F., E. R. Goode, R. S. B. Robertson and H. S. Sloane.
1953. In vivo measurement of body fat and body water in swine. J.
Applied Physiol. 6:27-32.

Siri,‘W. E. 1953. Fat, water and lean tissue Studies. Fed. Proc.
12:133.

Benne, E. J., N. H. Van Hall, A. M. Pearson. 1956. Analysis of fresh
meat. J.A.0.C. 39:937-945.

Hall, J. L. 1953. Ether extraction method of estimating degree of

fatness in carcasses and cuts. Proc. 6th Reciprocal Meats Conference.
p. 122-126.

JMitchell, H. H., and T. 8. Hamilton. 1929. Swine type studies. III.
The energy and protein requirements of growing swine and the utili-

zation of feed energy in growth. Univ. of 111. Agre. Expt. Sta.
Bull. 323.

29.

30.

31.

32.

33.

34.

-61..

Harrington, G. 1958. Pig Carcass Evaluation. Commonwealth Agricul-
tural Bureaux. Farnham Royal, Bucks, England.

Clawson, A. J., B. E. Sheffy, and J. T. Reid. 1955. Some effects of
feeding chlortetracycline upon the carcass characteristics and the

body composition of swine and a scheme for the resolution of the
body composition. J. Ani. Sci. 14:1122-1132.

Keys, A., and J. Brozek. 1953. Body fat in adult man. Physiol. Rev.
33:245-325.

Pace, N. and E. N. Rathbun. 1945. Studies on body composition. III.
The body water and chemically combined nitrogen content in relation
to fat content. J. Biol. Chem. 158:685-691.

Kirton, A. H., and R. A. Barton. 1958. Live weight loss and its com-
ponents in Romney ewes subjected to L-thyroxine therapy and a low
plane of nutrition. 1. Effects of live weight, carcass weight and
carcass composition. J. Agri. Sci. 51:265-281.

‘Moulton, C. R. 1923. Age and chemical deve10pment in mammals. J.
Biol. Chem. 57:79.

APPENDIX

-62-

Table 1. Summa of bod wei;ht and densit values
Live weight Live body density

 

Pig Air Helium
No. lbs Egg displacement dilution Theoretical
1 205.0 93.0 1.020 -- 1.033
2 196.0 88.9 1.066 -- 1.037
3 193.0 87.5 1.029 -- 1.035
4 220.0 99.8 1.031 -- 1.031
5 210.0 95.3 1.056 -- 1.015
6 183.0 83.0 1.106 -- 1.042
7 203.0 92.1 1.059 -- 1.026
8 206.0 93.4 1.066 -- 1.038
9 198.0 89.8 1.024 -- 1.030
10 211.0 95.7 1.023 -- 1.027
11 205.0 93.0 0.975 1.031 1.034
12 186.0 84.4 1.023 0.960 1.033
13 199.0 90.3 1.002 1.078 1.034
14 184.0 83.5 1.004 1.009 1.031
15 181.0 82.1 1.094 1.114 1.031
16 200.0 90.7 1.153 1.043 1.041
17 198.0 89.8 1.080 1.066 1.018
18 209.0 94.8 1.165 1.055 1.030
19 216.0 98.0 1.222 0.997 1.035
20 201.0 91.2 1.221 0.955 1.025
21 181.0 82.1 1.111 1.063 1.037
22 206.0 93.4 1.065 0.940 1.031
23 188.0 85.3 1.103 0.961 1.021
24 182.0 82.6 1.091 0.963 1.025
Mean 198.4 89.99 1.0745 1.0168 1.0308

 

-63..

669-36 88.- H .62 we...

 

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505 0.000 5.0 5.0 5.0 5.H 0.5 0.5 5.505 05
005 0.005 0.5 0.0 0.0 0.0 0.5 5.0a 5.005 05
005 0.00H 5.H 0.5 0.5 0.0 0.0 5.05 5.005 55
H05 0.005 0.H 0.0 0.5 5.0 0.0 5.0 0.005 H5
505 0.505 0.5 5.5 5.05 0.0 5.0 H.5H 5.505 05
055 5.005 0.5 0.0 5.05 5.0 0.5 5.HH 5.005 55
505 5.505 0.5 5.0 5.5 5.0 0.0 0.5 0.505 0a
055 0.505 0.0 5.0 5.5 5.0 5.5 5.5 0.005 5a
005 0.005 0.5 0.5 0.5 0.0 5.0 0.55 H.HOH 05
505 5.005 0.H 0.5 0.05 5.0 0.5 5.05 0.005 05
00a 0.505 5.0 5.0 0.0 0.0 0.5 5.5 5.005 05
555 5.505 0.5 0.0 0.05 0.5 0.5 5.0 5.005 0a
005 5.00H 5.5 5.0 0.5 5.0 5.5 5.5 H.50H 55
005 0.50H 0.5 0.0 5.55 0.5 5.5 0.55 0.005 AH
555 0.005 5.5 0.5 5.55 5.0 5.0 5.55 5.50H 05
055 5.505 0.5 0.5 0.HH 5.5 5.0 5.05 0.505 5
005 0.500 0.H 5.0 5.aH 0.0 0.5 0.55 0.50H 0
005 0.005 5.5 0.5 0.05 0.0 5.0 0.05 0.00H 5
005 5.505 0.5 0.5 0.5 0.0 0.5 5.5 5.505 0
055 0.005 0.5 0.5 0.05 0.5 0.5 0.05 0.50H m
055 0.055 5.5 0.5 0.05 5.0 5.0 5.55 0.505 0
055 5.005 0.5 0.0 5.5 0.0 5.55 0.005 0
05a 0.00H 0.5 5.5 5.05 0.0 5.0 5.5 0.505 5
005 0.005 0.05 5.5 0.0 0.0 0.5 0.05. 0.505 *5
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Hair

scurf

 

   
 

Kidneys-spleen
esophagus-trachea

Stomach

Percent ash of animal bod c

Table 6.

Head
tongue

Intestinal

caul fat
intestines

Dressed

carcass

Pig

toenails

Blood

contents

liver-lungs-heart

No.

 

0.92
1.31
1.31
1.31

1.20
1.20
1.20
1.20

10.22

2.05
2.41

1.27
1.16
1.19
1.17

0.88
0.99
1.08
0.87

3.27
2.61
2.69

9.07
7.71
8.49

2.08

C)
a:

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1.94
2.04
1.56
1.83
2.17
1.70

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F;

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0.90
0.88
0.80
0.85
0.77
0.75
0.79

2.99
2.95
3.07
2.71

2.

18
19
20
21

1.31
1.31
1.31
1.31

1.20
1.50
1.06
1.08

9.38
8.85
7.74
6.74

1.13
1.16
1.13

91

22

3.06
2.82

23
24

29.29 30.13

183.18

47.78

27.79

20.23

67.81

Total

1.31

1.22

7.63

2.08

1.16

0.84

2.83

Mean

 

-68-

 

 

 

 

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00000 0000 5005000005 0000000a000000000 00m 5000 0000000 00000 05m
0500 000500u000005x 0000000 50009

 

 

 
 

0000000 00000 0000 50000 00 00000 0 0000 0 00000500000 0000000 00000 000000m .0 05009

-70-

 

 

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50.05 05.0 «0.0 05.0 50.0 «5.0 55.50 00.0« 5
05500000 00050 000000 00000000 00000-00005u00>55 0005000005 0000000 0500000‘ .02
00000 0000 5005000005 0000000n000000000 000 5000 0000000 50009 050

0500 000500-0000050 0008000 .005

 

 
 

050000 000 50000 00 00000 800 0000 0 00000500000 050000 0000000 .0 05009

-71-

 

 

 

 

 

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-72-

 

 

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-73-

00000 .5.0 00 00000000 000005000 u 00-
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.00 00000

 

-74-

Table 13. Length! backfat thickness! and dressing gercentage data

Backfat thickness inches

 

 

Pig Length First Last Last lumbar Dressing
No. inches rib rib vertebra Average 4percent
1 -- - - - - --
2 -- - - - - 78.3
3 -- 1.5 _ 1.0 1.1 1.2 78.3
4 30.8 1.7 1.0 1.3 1.3 77.9
5 29.3 2.5 1.5 1.7 1.9 77.6
6 29.4 1.4 0.9 0.9 1.1 76.0
7 30.4 1.9 1.1 1.3 1.7 76.0
8 30.9 1.5 0.9 1.2 1.2 74.5
9 29.6 1.8 1.1 1.1 1.3 77.5
10 30.8 2.1 0.9 1.5 1 1.5 75.3
11 28.5 1.9 1.3 1.4 1.5 76.4
12 28.8 1.5 1.0 1.2 1.2 76.0
13 29.9 1.8 1.1 1.3 1.4 78.5
14 28.7 1.5 1.0 1.1 1.2 78.5
15 29.5 1.9 1.0 1.2 1.4 75.7
16 30.5 2.0 0.9 1.0 1.3 76.0
17 29.1 2.2 1.3 1.8 1.8 78.6
18 30.0 2.2 1.4 1.3 1.6 78.1
19 31.2 2.1 1.1 1.2 1.5 76.4
20 29.8 2.8 1.5 1.5 1.9 76.4
21 28.8 2.0 1.1 1.0 1.4 78.2
22 31.1 1.8 1.0 1.2 1.3 78.5
23 28.3 2.0 1.4 1.5 1.6 78.8
24 28.3 1.8 1.1 1.4 1.4 78.9

Mean 29.7 1.90 1.12 1.28 1.44 77.15

 

RGGé‘A USE LiY.

 

 

—~:_‘

     

   

LIBRAR'ES

“wrugmmmfli[1111171 "'1'“

4808

 

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