Photographic Methods of Measuring Longissimus Dorsi
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85. PHOTOGRAPHIC NETHOOS OF MEASURING LONGISSINUS DORSI JOHN Me STULL .......................................................KANSAS STATE COLLEGE The cross section view of the longissimus dorsi muscle has been accepted as a useful objective measurement of the quality of beef cattle car- casscs by the Committee on Cooperative Meat Investigations and the North Central Regional Beef Cattle Breeding Laboratory. This paper will describe the photogrcphic methcd of collecting these measurements as developed by Mr. William Stalls at the Kansas Agricultural Experiment Station. This technique was developed to facilitate the ease wfth which these msasuremcnts could be collected. The equipment used consisted of a Kodak 35 camera, econo-flash strobe light, SGries VI lens attachment with a one and one-fourth inch adapter ring, +1 portra lens and a frame on which to rest the camera. The lens attachment, adapter ring and the portra lens wcre required as the photographs wure taken at a close focal range of twenty-four inches. The frame was neccssary to hold the comer stationary and to insure the same focal range in each photograph. The frame was constructed of copper tubing, consisting of a ten by fifteen inch rectangular bottom piece to rest on the ribbcd carcass and two uprights which fastened on the camera. The two uprights were adjustriblo as to focal range and position over the rib face, A transparent ruler was taped across the upper end of the frame so that when the pictures were projected on a screen, they could be scaled to actual size (Slide No. 1). Several tests were conducted to determine the accuracy of the photographic method and to develop a satisfactory technique. In the first test, fine grained plus X Panchromatic film and a focal range of twenty-four inches were used. The camera lens opening was set at F8, referred to as the F stop and the exposure time or shutter spaed at 1/100. Although these photographs were satisfactory for measuring purposes, they exhibited a tendency to be slightly over-exposed and the optimum amount of desired detail was not present. Further tests were conducted using Pantomic X film, an ultra fine grain film, different F stops and shutter speeds. Most satis- factory results were secured by using Pantomic X film and a camera adjustment of F/16 lens opening and a shutter speed of 1/100. A model 3A Kodaslide Projector was used to project the negative of the rib cut on a sixteen by twenty-five inch frosted glass field (Slide No. 2). The actual .siee of the rib cut was obtained by holding a plastic ruler on the frosted &ass, adJusting the projector until the ruler in the projected negative coincided with the ruler being held against the glass. Tracings were made of the rib cut in the projected negative by taping a sixteen by sixteen inch sheet of parchment paper on the frosted glass facing the projector and tracing the outline of the cross-scction of the longissimus dorsi and adjoining parts of the parchent paper. The measursments of the rib eye and external fat were madc from this tracing (Slide No. 3). The measurements made are illustrated in Slide No. 4. The area measurement was made with an Amsler compensating polar planimeter. Tha werage of three readings from the planimeter w&s used to determine the total area of the eye muscle. The length measurement was the longest 86. distance across the eye muscle (AB). The width was an average of the follow- ing measurements: A line (CD) perpendicular to AB and one-half the distance from A to B; a line (GH) perpendicular to AB and one-half the distance from B to P; a line (EF) perpendicular to AB and one-half the distance from A to P. The thickness of fat was an average of three measurements (LF,MD,NH), measured from the outside of the fat where the surface of tho fat is perpen- dicular to these points, F,D and H. A rib eye index was calculated by dividing the rib eye width into rib eye length and multiplying the answer by 100. The accuracy of the photographic method was checked against measure- ments made from original tracings. Slide No. 5 gives the measurements and the correlation coefficient obtained. A correlation coefficient of +0.982 between the two methods indicates that the photographic method can be used with confidence. To f’urther test the accuracy of the photographic method, ten parchment Faper tracings and ten photographs were taken of the same rib cut. The error variance and the coefficients of variability (.9$ and 1.1%) of the two methods were determinod. The results are shown in Slide No. 6. The coefficients of variability me extremely low, rendering both methods equally accurate and highly reputable. This photographic method is recornended for facilitating the ease with which these measurements can be made, in decreasing the confusion caused by a data-collecting crew in the packing house cooler, and permitting the tracings to be made at a later date. 87. CORRELATION BETWEEN PHOTOGRAPHIC METHOD AND THE ORIGINAL TRACING ----METHOD X Y carcass Measurements Obtained Measurements Obtalned Number From Projected Negative- From Original Tracing Square Inches Square Inches 1 9.55 9.39 2 10.46 10.77 3 9.45 9.46 4 8.82 8.97 5 10.17 10.22 6 9.55 9.75 7 7.43 7.73 8 9.26 9.46 9 8.36 8.60 10 10.60 10.33 - X ( X2 ) 885.5425 S (Y2)903,5418 COEFFICIENT OF CORRELATION +o. 982 ___ __ - I_ I___ - ERROR VARIANCE AND COEFFICIENTS OF VARIABILITY OF THE TWO ME230DS OF--- MEASURING THE EYE MUSCLE Number of Tracing -From - Square Inches Square Inches 1 12.12 I 12.26 2 12.06 I 12.45 3 12.19 I 12.30 4 12.33 I 12.18 5 11.97 12.33 6 12.14 12.12 I 7 12.12 I 12.18 8 12.30 1 12.09 9 11.97 I 12.06 10 12.19 I 12 .oo ERROR VARIANCE = 0.37 COEFFICIENT OF VARIABILITY = 0.9%,1,1'% 88. MR. NAUMANN: Thank you. Marshall Heck, of the University of Arkansas, will now lead the discusslop. MR. HECK: How much time does it actually save? How long does it take? MR, McINTOCH: Well, it takes about a fraction of a minute to take the photograph after the carcass is in position. On one pasticu- lar setup where we were using Army beef we made all our measurements in the afternoon when the beef carca8ses were selected and the next morn- ing when they were going on the cutting floor we caught them just as they were passing and we got our measurements that time in that manner. In other cam8 we just flashed them and we had the record when the carcass wa8 free. It is usually necessary to borrow a stool, but we find these shrouding benches a very convenient height, and since most of them are on wheels you can wheel them down the line and get several carcasses on the line. MR, BUTLER: This may be a little extraneous, but you drew your lines out for measuring the thickness of fat covering the rib eye 88 shown in this diagram? MR, BECK: Correct. MR. BUTLER: I thought the tracing handed out last year recom- mended that the line from the rib surface of the eye be perpendicular instead of straight out. MR. McXSlQSH: This particular picture and the one we used were made from some measurements we were making in the cooperative grading project which stated that they should be made in this manner. In other words, it was a projected procedure in this case. CEAIRMAN COLE: Dr. Peareon and his Research Methods Committee have worked very hard. He has a pretty ambitious report to give to us, dividing it up into two sections, degree of fatness on the live animal and in the carca8s. So, Dr. Pearson, without any further ado, we are going to let you take over. ####### .