Department of Animal Science Florida Agricultural
Mimeograph Series No. 62-7 Experiment Station
November, 1961 Gainesville, Florida
VARIABILITY OF RIB EYE AREA AND APPARENT DEGREE OF MARBLING OF
BEEF CARCASSES AS INFLUENCED BY METHOD OF RIBBING-/
J. W. Carpenter, A. Z. Palmer and R. L. ReddishZ/
Rib eye area has been shown to be a useful indication of the degree of
muscling or meatiness of the beef carcass. A highly significant correlation
coefficient of 0.853 between percentage of edible portion and area of the
L. dorsi muscle at the 12th rib was reported by Cahill et al, 1956. Yield
grading of beef carcasses as developed by the U.S.D.A. is based upon rib-eye
area, thickness of fat over the eye, percent kidney fat and carcass weight
to estimate carcass meatiness of carcass cut out value. A procedure for
obtaining rib eye area presented by Naumann (1952) indicates that the L.
dorsi muscle should be cut between the 12th and 13th ribs with the knife held
perpendicular to the carcass and following the contour of the 12th rib.
Many packers vary this cut from just below the 13th rib to the other extreme
of burning the 12th rib. It appears that many variations of Naumann's recom-
mendation are being used in carcass evaluation studies and in carcass contests.
With such an emphasis being placed on rib eye area, it would seem that
the measurement procedure should be standardized and accurately taken if
it is to be used with confidence in evaluation the muscling, meatiness or
cut out value of beef carcasses.
The purpose of this study was to compare the rib-eye areas of the
right and left sides of beef carcasses ribbed by different methods. Another
purpose was to determine the difference, if any, in apparent degree of
marbling due to method of cutting assuming degree of marbling to be equal
in each side of the carcass.
One hundred and forty-nine beef carcasses were used in this study from
cattle of mixed British, Brahman, and Charolais breeding, fed at Florida
Branch Experiment Stations and slaughtered at the University Meats Labor-
atory. The cattle were approximately sixteen months of age at the time of
slaughter and had been fed in dry lot for 180 days.
The left side was ribbed by cutting across the lumbar vertebra half
way between the 12th and 13th rib and continuing the cut midway between the
ribs following the contour of the ribs. The right side was ribbed by
cutting across the lumbar vertebra half way between the 12th and 13th rib
I/ The assistance of Mrs. Norma Bowles and Mr. Richard Newman, Laboratory
Assistants, and Jeff Jeter, Meats Laboratory Manager, Animal Science
Department, University of Florida, is acknowledged.
2/ Carpenter, Asst. Meat Scientist; Palmer, Assoc. Meat Scientist; Reddish,.
Assoc. Extension Meats Specialist; Animal Science Department University'r .
of Florida, Gainesville, Florida. ,
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perpendicular to the long axis of the L. dorsi muscle and striking the top
of the 12th rib just beyond the eye muscle. Outline tracings were made of
each L. dorsi muscle and the area determined from the tracings by use
of the compensating polar planimeter. :
Degree of marbling was determined on each rib eye.by,a Federal Meat
Grader. Terms used in this'study to indicate degree of marbling were:
devoid, practically devoid, traces, slight, small, modest, moderate, slightly
.abundant, moderately abundant, abundant, very abundant and extremely abun-
dant; scores were assessed on a plus, minus or average basis.
Differences,between paired sides in rib eye area and degree of marbling
were tested by use of the "t" test.
RESULTS AND DISCUSSION
In general, rib eyes exposed by cutting on the bias were larger than
those obtained by cutting perpendicular to the L. dorsi. Left side rib eye
areas were from 0 to 35 percent larger than right side areas. In three
.carcasses right side eyes were slightly larger thah left side eyes; the
greatest difference was only 0.13 sq. in. and such a difference could have
been due to a tracing or measuring error rather than a real difference.
The extent to which the left side eyes were larger than right side eyes
is shown in Table I. It may be seen that in 93 percent of the carcasses the
left eye area exceeded the right eye area from 0 to 25 percent; in 70 percent
of the carcasses, the left eye area exceeded the right eye area from 5 to 20
percent. Average rib eye areas were 9.44 sq. in. and 8.76 sq. in. for the
left and right sides, respectively. Differences between left and right
side rib eye areas were highly significant (P<0.005).
THE EXTENT TO WHICH LEFT RIB EYE AREAS EXCEEDED RIGHT RIB EYE AREAS AND
DIFFERENCES IN AVERAGE DEGREE OF MARBLING BETWEEN LEFT AND RIGHT RIB EYES.
No. of Carcasses Left eye area larger Degree of Marblingil
in each group than right eve area Left eye, av. Right eye, av.
3 by 0 % 14.67 14.00
18 by 0-5 % 13.22 13.61
S 24 by 5-10 % 11.74 11.09
48 by 10-15 j 12.96 12.10
33 by 15-20 13.94 12.72
16 by 20-25 % 12.19 11.44
3 by 25-30 % 15.75 13.25
4 by 30-35 % 11.00 9.50
1/ 9 traces 10 = slight -, II slight, 12 = slight +,
13 = small-, 14= small, 15 = small + and 16 = modest -.
Differences in degree of marbling between the left and the right
sides were highly significant (P<0.05). The left side cut packer style,
or on the angle, appeared to have a greater amount of marbling than did
the right side ribbed perpendicular to the long axis of the L. dorsi
muscle. Table I shows a consistently greater amount of marbling in the
left eye over the right eye in all but one group. In this group the
variations in loin eye area from right to left ranged from zero to five
per cent and the right side had slightly more marbling than the left.
Perhaps by cutting on an angle, marbling appeared larger, denser or more
evenly distributed over a greater area than when confined to the smaller
area of the right eye. The average difference in marbling between the
left and right eyes amounted to slightly less than one-third degree of
marbling, however, as much as two full degrees of marbling difference
was noted in several carcasses.
These data suggest that it would be advantageous, in-so-far as
quality grade is concerned, to cut a long angle eye rather than straight
across the rib eye since a larger percentage of the carcasses cut larger
eyes and displayed more marbling in the left eye than in the right eye.
Cahill, V. R., L. E. Kunkle, E. W. Klosterman, F. E. Deatherage and E.
Wierbicki. 1956. Effect of Diethylstilbestrol implantation on
carcass composition and the weight of certain endocrine glands of
steers and bulls. Ohio Agr. Exp. Sta., Columbus. J. Animal Science,
Haumann, H. D. 1952. A recommended procedure of measuring and grading
beef for carcass evaluation. Proc. of the 5th Annual Reciprocal Meat
Conference, p. 108.