PORK & PORK QUALITY                               PIH-42


                         Carcass Evaluation

Robert G. Kauffman, University of Wisconsin
Richard J. Epley, University of Minnesota
Tom R. Carr, University of Illinois

John C. Forrest, Purdue University
Allen Keppy, Wilton, Iowa


     Carcass evaluation is an important part of  determining  the
success of pork production.  Following reproduction, feeding, and
marketing of the hog, the final step is transformation into  food
for  humans.   Through these processes, pork producers can effec-
tively evaluate their progress in selection and  management.   In
addition  to  measuring  efficiency  in terms of producing large,
healthy litters that gain rapidly on minimum feed, producers also
should  be concerned about how much lean, edible pork is produced
and how desirable that lean is for processing and consumption.

     This fact  sheet  describes  compositional  and  qualitative
characteristics associated with pork carcass desirability, and it
identifies procedures that can be  standardized  and  applied  to
measure  these  characteristics  throughout  the  pork  industry.
Every market hog should have its carcass  evaluated  for  weight,
wholesomeness,  composition and quality.  Identification of these
traits serves  as  an  incentive  for  packers  to  differentiate
economic value.

Evaluating Pork Carcasses

     Identification. Marked with approved edible  ink,  each  hog
should  be  tattooed  at two locations on each side.  If hogs are
skinned rather than dehaired, tags can be clipped to  both  ears.
After  bleeding  and  before  the  head  is removed, the tags are
removed, placed in a plastic bag and securely pinned to the fore-

     Inspection. The inspector  at  the  slaughter  plant  should
record   information  concerning  abnormalities  observed  during
antemortem and postmortem inspection.  Even though carcasses pass
inspection,  abnormalities  such  as jowl abscesses, arthritis or
cryptorchidism should be reported to  producers.   It  is  recom-
mended  that  such  carcasses  not  be  evaluated further because
genetic stock susceptible to these  conditions  should  be  elim-
inated from the gene pool.

     Warm-carcass weight, belly dimension  and  trimming  losses.
The  warm-carcass weight should be written on the carcass with an
edible ink marker.  If time and space do not permit this,  weight
may  be  recorded  sequentially on a weigh sheet.  Writing on the
carcass helps minimize errors in matching weights with  identifi-
cation numbers.  If cold carcass weights are recorded, convert to
a warm-weight basis by dividing by 0.985 because  most  carcasses
shrink  about  1.5% during drying and chilling.  For skinned car-
casses, adjust to a skin-on basis by dividing the warm weight  by
0.94 (the skin accounts for about 6% of the warm-carcass weight),
or by another appropriate value provided by the plant management.

     If jowls are removed or if muscle, fat  or  bone  have  been
removed from locations where measurements are taken, or if exces-
sive (greater than 5% of warm-carcass weight) muscle, fat  and/or
bone  have  been removed by inspectors, the carcass should not be
included in a carcass  contest  because  the  carcass  cannot  be
evaluated  accurately.   If  the  trim  loss is less than 5%, the
amount missing should be estimated and added to the  warm-carcass

     Although a minimum carcass weight of 150 lb  is  recommended
for  carcass  contests,  the acceptable weight range should match
the weight preference of the cooperating packing plant.  If  thin
bellies  are  a  concern at this weight, then the minimum carcass
weight requirement should be increased.  To  date,  there  is  no
reliable  objective definition of a belly that is too thin.  Most
carcasses weighing 150 lb or more will be free of the  thin-belly
problem.   Once  bellies  meet  minimal dimensions for subsequent
processing, the major concern is desirable composition and  qual-

     Ribbing the carcass. To measure muscle composition and qual-
ity  characteristics,  the  vertebra  of the untrimmed carcass is
first cut perpendicular to the long axis of the loin between  the
10th and 11th ribs.  Start adjacent to the 11th rib and just cra-
nial to the 10th - 11th thoracic vertebrae junction to  permit  a
square cut across the loin muscle and avoid cutting the 10th rib.
After the vertebra is sawed, use a knife and extend  the  cut  no
more  than one inch beyond the outer side of the loin muscle sur-
face.  Extending the cut further will damage the belly.   Ribbing
should  be  done  only  on properly chilled carcasses (at least 6
hours for surface freezing procedures or  12  hours  for  conven-
tional  chilling  procedures after slaughter is recommended);  it
should be completed at least 10 minutes prior to visual  examina-
tion to allow for full expression of the quality characteristics.

Composition Characteristics

     Composition refers to the proportionate amount of  lean  (or
muscle) that a carcass contains.  Degree of fatness and extent of
muscling (reflecting variations in muscle-bone ratio) are the two
important  factors  associated with composition.  It is desirable
to have as much muscle and as little fat, bone and skin  as  bio-
logically  possible without jeopardizing quality and live produc-
tion factors.  When comparing carcasses or  measuring  production
efficiency, it would be ideal to determine the proportion of mus-
cle by physical dissection and  chemical  analysis,  or  by  some
other  procedure  such as electromagnetic scanning (TOBEC).  How-
ever,  these  procedures  are  not  practical  under  most   cir-
cumstances.   Simpler  (and  less  accurate)  methods are used to
estimate composition.  The following measurements can be combined
to estimate the composition of the carcass:

o    Warm-carcass weight (adjusted for missing parts).

o    Fat depth (including skin) over the loin at  the  10th  rib.
     Visually  divide  the  longest  axis (the width) of the loin
     muscle surface into quarters.  Measure the fat  depth  oppo-
     site  a  point  that is 3/4 the distance along the long axis
     closest to the belly.  The measurement is taken in  .05-inch
     units  from the edge of the loin muscle to the outer edge of
     and perpendicular to the skin (see Figure 1).   For  skinned
     carcasses,  add  0.1  inch  to the measurement.  For greater
     accuracy, both sides of the carcass should be ribbed,  meas-
     ured and averaged and reported to the nearest 0.05 inch.  No
     minimum fat thickness is recommended because there is little
     or  no  information  to support a minimal acceptable fatness
     level.  As long as selection against fatness does not result
     in  muscle  quality  deficiencies,  thin  belly  concerns or
     reduced live production efficiency,  pork  producers  should
     continually attempt to reduce fatness.

o    Loin muscle area (LMA).  This measurement is made in  square
     inches  by  using  a  clear plastic grid (Grid AS-235e, Iowa
     State University, Ames).  Loin muscle area is determined  by
     measuring  the cross-sectional area illustrated in Figure 1.
     The area also can be measured by tracing the outer perimeter
     of the loin muscle on acetate paper and using a compensating
     polar planimeter to measure the area.   For  more  accuracy,
     both  sides of the carcass should be ribbed and measured and
     the values averaged and reported to the nearest  0.1  square

o    Carcass muscling score (See Figure 2).

o    Equations to estimate carcass lean.

     Combine warm-carcass weight, fat depth, and loin muscle area
or  muscling  score to estimate pounds or percentage of lean pork
(containing 5% fat).  The first two  equations  can  be  used  to
estimate  pounds  of lean pork when carcass weight is adjusted to
170 lb.  This adjustment is  needed  when  live  weight  and  age
differences  need to be minimized, for example, in comparing car-
casses in competition.

Equation 1.
Pounds of acceptable quality
lean pork (containing 5% fat) = 88.307
- (adjusted warm-carcass weight, lb x .036)
+ (loin muscle area in square inches x 3.734)
- (10th rib fat depth in inches x 18.574)

If the carcass cannot be  ribbed,  then  the  following  equation
should be used:

Equation 2.
Pounds of acceptable quality
lean pork (containing 5% fat)= 88.506
- (adjusted warm-carcass weight, lb x .045)
+ (muscling score x 6.062)
- (last rib fat thickness in inches x 15.077)
+ 3.957 (if sex = gilt)

     To determine percentage of lean pork in the carcass,  always
divide  pounds  of lean pork by 170 and multiply by 100 for equa-
tions 1 and 2.  When circumstances dictate that weight should not
be  held constant (i.e., when carcasses are evaluated for current
worth), then use Equations 3 or 4.

Equation 3.
Pounds of acceptable quality
lean pork (containing 5% fat) = 7.231
+ (adjusted warm-carcass weight, lb x 0.437)
+ (loin muscle area in square inches x 3.877)
- (10th rib fat depth in inches x 18.746)

Equation 4.
Pounds of acceptable quality
lean pork (containing 5% fat) = 8.179
+ (adjusted warm-carcass weight, lb x 0.427)
+ (muscling score x 6.290)
- (last rib fat thickness in inches x 15.596)
+ 3.858 (if sex = gilt)

     To determine percentage of lean pork in the carcass,  divide
pounds of lean pork by actual warm-carcass weight and multiply by
100 for Equations 3 and 4.

Qualitative Characteristics

     Desirable fresh pork quality is defined as a combination  of
traits  that  provide  an  edible product that loses a minimum of
water and nutrients, is wholesome after processing  and  storage,
is  attractive  in  appearance, and is appetizing, nutritious and
palatable after cooking.  Nutritive value is basic to pork  qual-
ity; the primary merit of pork as a food is its nutrient content.
Pork muscle contains proteins made  up  of  the  essential  amino
acids in biologically available form; the water-soluble vitamins,
especially thiamin; some minerals, notably  iron  and  zinc;  and
high-energy lipids, including the essential fatty acids.

     Wholesomeness refers to cleanliness  and  the  freedom  from
undesirable  microorganisms, which is influenced by the health of
the live hog and by proper sanitation during  slaughtering,  han-
dling  and storage of pork.  Together, nutritive value and whole-
someness satisfy the minimum requirements for pork to be used  as

     Suitability for processing relates to  pork  which  sustains
minimal  shrinkage because the muscle is not watery.  Attractive-
ness is an  aesthetic  factor  determined  by  color,  structural
appearance,  and  convenience (size of cut, amount of bone, etc.)
for use as food.   Palatability  characteristics  include  flavor
(taste and aroma), tenderness, texture and juiciness.

     For more  information,  refer  to  the  publication  by  the
National Pork Producers Council*(NPPC) that includes a discussion
on the variation in pork quality that  currently  exists  in  the
industry.  The following quality traits are related to shrinkage,
appearance and palatability; they are useful predictors for  pork

     Muscle color.  Fresh pork should be reddish  pink.   Indivi-
dual  muscles  are  usually  uniform in color, but muscle groups,
such as in the ham, often  display  considerable  variability  in
color.   Dark color may result from increased quantities of color
pigments, greater preslaughter physical  activity,  less  surface
oxygen  or  surface  dehydration, or minimal production of lactic
acid during carcass chilling.  A pale pinkish gray color  may  be
the  result  of  a  rapid conversion of muscle glycogen to lactic
acid immediately after slaughter.

     Muscles that are too pale or too dark are  objectionable  in
appearance in retail trade.  Abnormally pale muscles quickly turn
gray in the retail display  case  and  often  incur  considerable
shrinkage, resulting in economic losses, and dry-tasting products
after cooking.  Dark muscles  will  have  a  shorter  shelf  life
because  they  are  less  acidic  and therefore support bacterial
growth; they are considered by some consumers to  originate  from
older  animals.   The  five  color  scores shown in Procedures to
Evaluate Market Hogs** (1 = Pale pinkish gray, 2 = Grayish  pink,
3  =  Reddish  pink, 4 = Purplish red and 5 = Dark purplish red.)
represent normal  variation  of  pork  color.   Carcasses  having
either  of the two extreme color scores should be eliminated from
consideration in carcass competition.

     Muscle firmness-wetness condition.  If the  loin  muscle  is
soft and exudative, displaying obvious fluid accumulations on its
surface and exhibiting a coarse texture, the  carcass  should  be
eliminated  from  competition.   This condition is related often,
but not always, to the pale color, and such a product often  sus-
tains  excessive  shrinkage  during  processing.  The meat is dry
when eaten.  For visual firmness scores, see NPPC's Procedures to
Evaluate Market Hogs.**

     Marbling.  Marbling is the visible fat within the boundaries
of  the  loin  muscle  area.  Slight to small amounts as shown in
Procedures to Evaluate Market Hogs** are desirable to  provide  a
juicy  and  flavorful  cooked  product.  Pork with traces or less
marbling may be less flavorful and less juicy than desired.  How-
ever,  abundant  marbling does not make pork proportionately more
palatable but does supply more calories,  thus  making  the  pork
products  objectionable  to most consumers.  Carcasses possessing
muscles devoid of marbling or having abundant quantities of  mar-
bling  should  be  eliminated from competition unless it is for a
herd evaluation.

     Abnormalities.  Pork fat should be firm  and  white.   Soft,
oily  or  slightly  brownish-colored  fat  is not attractive when
displayed at the market place and is more susceptible  to  ranci-
dity during processing and storage.

     Other abnormalities affecting the acceptability of pork mus-
cle  include fatty infiltration and blood splashing.  Such condi-
tions are rare, but if present, the carcass should be  eliminated
from competition.

Table 1.  Recommended minimum standards for pork carcasses to  be
eligible for competitive evaluation program**.
             Carcass trait           Minimum eligible values
             Cryptorchidism          must be absent
             Adjusted warm weight    >150 lb
             Length                  > 29.5 in
             Muscling Score          > 2.0
             10th-rib fat depth      < 1.30 in
             Last rib fat thickness  <  1.20 in
             Loin muscle area        > 4.5 in
             Total lean content      > 43.0%

             Color                   Grayish pink to purplish red
                                     (NPPC Scores 2-4)
             Firmness/Wetness        NPPC Score > 3
                                     (Slightly firm and moist)
             Marbling                Traces to slightly abundant
                                     (NPPC Scores 2 to 4)
**  National  Pork  Producers  Council.   1991.   Procedures   to
Evaluate  Market  Hogs,  3rd  Ed., P.O. Box 10383, Des Moines, IA

Combining Composition and Quality Traits
of the Carcass with Live Production Traits

     If carcasses are to be ranked on the basis of overall merit,
then  (a)  each  carcass should be free of all abnormalities; (b)
the loin muscle must meet minimum standards  for  muscle  quality
and have a warm-carcass weight of at least 150 lb (See Table 1).

     Carcass excellence in itself is desirable  but  is  not  the
ultimate  answer  to successful pork production.  Factors indica-
tive of carcass quality and composition should be  combined  with
live  visual  traits  and production records as described in Pro-
cedures to Evaluate Market Hogs**. Pounds of  acceptable  quality
lean  pork  gain per day on test should be implemented to measure
more realistically overall progress in  pork  production,  rather
than simply to evaluate carcasses on the basis of their lean per-
centage and quality.  The following equation can be used to  cal-
culate quality lean gain per day on test.

Pounds of acceptable quality lean pork (containing 5%  fat)  gain
per day on test
= [Pounds of lean in the carcass
  - Pounds of lean in the pig at the start of the test]
- days on test

Where pounds of lean in the carcass
= 7.231
+ (0.437 x adjusted warm-carcass weight, lb)
- (18.746 x 10th rib fat depth in inches)
+ 3.877 x 10th rib loin muscle area in square inches)

And where pounds of lean in the pig at the start of the test
= (0.418 x starting live weight, lb) - 3.650


     Equations in this publication were developed  from  a  study
that  included  361  carcasses  that  possessed a mean _ standard
deviation for 3/4 fat depth at the 10th rib (1.16 _ 0.3  inches),
for  loin muscle area (4.9 _ 0.7 square inches), for warm-carcass
weight (171 _ 14 lb) and for percent lean (46.9 _ 4.8, containing
5%  fat).   Researchers  randomly  purchased  231 barrows and 130
gilts from many sources.  This sample represented a population of
hogs  typically  found  at  the  market.   (Orcutt,  M. W., J. C.
Forrest , M. D. Judge, A.  P. Schinckel and  C.  H.  Kuei.  1990.
Practical  means  for  estimating  pork  carcass composition.  J.
Anim. Sci. 68:3987.)

* Kauffman, R. G.,  R. G.  Cassens,  A. Scherer and D. L. Meeker.
1992.Variations in Pork Quality. National Pork Producers Council,
P.O. Box 10383, Des Moines, IA

List of Figures
Figure 1.  Loin muscle area and fat depth at 10th rib location.

Figure 2. Carcass muscling scores

REV 12/92 (7M)

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