Abstract
A Simple Ultrasound Instrument is an Effective Tool in Predicting
Body Composition of Live Pigs.
Lee I. Chiba
Background Information & Objective
Assessing the body composition of live pigs is important in making
selection and marketing decisions and in studying nutrition,
physiology or growth of pigs. The use of the ultrasound technology
to estimate in vivo body composition of animals has a long history.
At present, numerous ultrasound instruments with varying complexity
are available, but there seem to be considerable variations among
complex, real-time ultrasound instruments in the efficacy of
estimating body composition. The use of complex ultrasound instruments
can be justified only if their additional costs of instruments
and operation are more than offset by benefits in extra precision.
Data collected from pigs that had been used in several nutrition
experiments were used for regression analyses to evaluate the
efficacy of a simple ultrasound instrument capable of measuring
only backfat (BF).
Source of Data, Procedures, Results & Summary
Data collected from 177 crossbred gilts (n = 88) and castrated
males (n = 89) were used to describe the relationship between
ultrasound BF measurements and(or) other independent variables
and carcass traits and lean in market weight pigs. Pigs were
housed either individually (n = 69) or as a group (six per pen;
n = 108) and were fed diets containing diverse levels of amino
acid (4.75 to 11.20 g lysine/kg) from 20 kg to market weight
(91 to 124 kg). When pigs approached market weight, BF thicknesses
were measured 4 to 5 cm from the midline at the third rib, last
rib and last lumbar vertebra using a simple, digital readout
ultrasound instrument (Renco Lean-Meater). After slaughter, carcass
BF were measured at the midline of corresponding positions. In
addition, other standard carcass measurements were collected,
and carcass specific gravity was determined by hydrostatic weighing
of the right side. The age of pigs at the time of slaughter was
also recorded. Appropriate statistical analyses were conducted
to describe the relationship among variables and to develop multiple
regressions. The best equations were chosen based on R2, standard
error of estimate and P-value for the regression coefficient
and standard deviation for the regression model (Sy.x). All regressions
were developed within sex, and for the combined data set. The
ultrasound instrument seemed to underestimate carcass BF, which
agrees with previously published reports. Differences in the
anatomical location of measurements and(or) changes in fat tissues
during the chilling process may partly explain those differences
between ultrasound and carcass BF. The average ultrasound BF
was highly correlated with carcass BF (r = .82) and percentage
of carcass lean (r = -.79), but only modestly with weight of
lean (r = -.32). The equations based on ultrasound BF and live
measurements accounted for 78 to 83% of variation in predicting
average carcass BF and weight of lean in gilts and castrated
males. Similarly, the equations based on live measurements accounted
for 80 and 79% of variation in predicting carcass BF and weight
of lean, respectively, in the combined data set. Regression analyses
for the 10th rib BF resulted in similar R2 value (.79), but the
Sy.x was higher than that obtained for the average BF. For the
percentage of lean, prediction models had slightly lower R2 (.73),
and the Sy.x was 1.44% for the combined data set.
In summary, partial correlations between ultrasound measurements
obtained by using a simple instrument and actual carcass traits
in the present research were very similar to those reported
for the real-time ultrasound instruments. The precision for
the prediction equations for carcass BF or weight of lean,
likewise, seemed to be equal to or better than those reported.
Measuring BF with an instrument used in this research is very
simple because of its size, weight and simplicity of operation.
Although neither a contemporary comparison of different instruments
nor actual dissection of carcass to estimate lean was made
in this research, the results indicate that the use of a simple
ultrasound instrument is a practical and effective means to
estimate carcass traits and composition of live pigs in studies
of nutrition, physiology or growth, or in making selection
and(or) marketing decisions.
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