Abstract:
Animal Production in Australia 1998 Vol. 22 THE USE OF COMMERCIALLY DETERMINED EYE MUSCLE AREA IN THE APPRAISAL OF BEEF CARCASES C. PORTERA and E.R. JOHNSONB A B PO Box 509, Sutherland, NSW 2232 Division of Farm Animal Studies, The University of Queensland, PO Box, 125, Kenmore, Qld 4069 SUMMARY Eye muscle area, measured four ways in 100 heavy steer carcases, was examined to determine its usefulness in the quantification of carcase lean. The four measurement techniques were fastbatelectronic pen, video image analysis, cellulose acetate grid with no time limit on the operator, and the grid used for a few seconds by the chiller assessor. The mean measurements of the four methods did not differ significantly, although the video image analysis measurements had a higher standard deviation. Areas measured by each of the four methods were highly correlated and each was very highly correlated with estimated lean meat yield calculated without using eye muscle area. This suggested that area, derived by any one of the four methods, was of approximately equal value. However, because all estimated lean meat yields calculated with the respective area measurement were very highly correlated with estimated lean meat yield calculated without area, and none of these yields differed significantly, eye muscle area did not contribute to the quantification of carcase lean. The measurement is not recommended for use in the quantification of lean meat yield. Keywords: beef cattle, eye muscle area, carcase appraisal INTRODUCTION There are two major concerns when considering the usefulness of eye muscle area in predicting carcase lean. The first is, can it be measured accurately in the live animal? The second question is, how useful to the prediction is an accurate eye muscle area? In relation to in vivo scanning and carcase measurements, Jansen et al. (1985) noted that a high relation does not necessarily imply a good prediction of body composition. In fact, over 50 years, accumulated evidence suggests that eye muscle area, used alone, is a poor indicator of carcase muscle (Walker and McMeekan 1944; Cole et al. 1960; Goll et al. 1961; Kempster et al. 1981; Priyanto 1993). When Kempster et al. (1981) included eye muscle area in multiple regression equations to predict carcase lean, they found it of little use. Johnson (1996) noted that the contribution of eye muscle area to the quatification of carcase lean depended on the weight range of the carcases being studied. Priyanto (1993) found fat thickness a poor predictor of carcase composition in heavy, fat carcases whereas Johnson and Priyanto (1991) showed that in such carcases, it was necessary to add eye muscle area to carcase weight and fat thickness in order to obtain a modestly accurate prediction of carcase muscle. The authors of the current paper have noted, that in many Australian meat processing plants, chiller assessors, using a cellulose acetate grid, measure eye muscle area very quickly, taking only a few seconds. This paper reports the relative accuracies of eye muscle area, measured four different ways in the carcase, in quantifying muscle. MATERIALS AND METHODS A meat processing plant on the east coast of Australia provided 100 carcases for measurement. The carcases were derived from 100 grass-fed steers (89 Brahman cross-bred and 11 Hereford or Limousin crossbred) and weighed from 210.5 kg to 395.0 kg (mean 327.1). Measurements were made on the right side of each carcase which weighed from 105.3 kg to 197.5 kg (mean 163.6; s.d. 17.5). Rump P8 fat thickness ranged from 4 to 34mm (s.d. 5.6). Eye muscle area at the 10th rib was measured in four ways: with a fastbat electronic pen (FB), by video image analysis (VIA), with a grid by one of the authors with no time limit (CP), and by a chiller assessor using a grid for a few seconds (CA). Estimated lean meat yield was calculated from carcase weight and fat thickness, and from carcase weight, fat thickness and eye muscle area, using areas measured by the four different methods. The equations, which were developed by Johnson (unpublished), using data from 74 grass-fed heavyweight, Brahman cross-bred carcases, anatomically dissected to determine composition, were: 209 Animal Production in Australia 1998 Vol. 22 y = 7.453 - 0.395 P8 + 0.546 HSW (s.e.m. � 4.28 kg; R2 = 0.83) where: y is side muscle weight (kg); P8 fat thickness in mm; HSW is hot side weight (kg). y = -3.544 - 0.313 P8 + 0.459 HSW + 0.316 EMA 2 (s.e.m. � 3.73 kg; R 2 = 0.88) EMA is eye muscle area at 10th rib (cm ) measured with a transparent cellulose acetate grid. Data were analysed using Pearson correlation coefficients and tests of significance. RESULTS The mean and range of the eye muscle areas, measured by four techniques are shown in Table 1. Video image analysis measured a greater range of eye muscle areas with a higher standard deviation, and the CA means were the highest, but no means differed significantly. Correlations between the four eye muscle area measurements and the other carcase measurements are shown in Table 2. All area measurements were highly correlated with each other. Video image analysis showed slightly lower correlations (0.86 and 0.88) than the other techniques (0.94 and 0.95) but none of the methods of measurement differed significantly. Side weight was moderately correlated with all eye muscle area measurements (0.55 to 0.58). Table 3 shows correlations between eye muscle area measurements and estimated lean meat yields. Correlations of all four area measurements with estimated lean meat yield, calculated without eye muscle area, were modest (0.61 to 0.65). All estimated lean meat yields (using eye muscle area) were highly correlated with their respective eye muscle area measurement (0.68 to 0.74). Side weight was the primary determinant of estimated lean meat yield. All estimated lean meat yields, using areas measured by the various techniques, were very highly correlated (r = 0.99). Estimated lean meat yield, calculated without eye muscle area, was very highly correlated with estimated lean meat yield, calculated with each eye muscle area measurement (r = 0.99). Table 1. Eye muscle areas recorded by the four methods of measurement Eye muscle area (cm ) Measurement FB VIA CP CA a a 2 Range 4 4 4 5 6 4 9 0 1 1 1 1 0 1 0 1 1 8 4 6 Mean 73.9 73.6 74.3 77.8 s.d. 11.4 13.1 11.6 11.7 Eye muscle area measured by one of four methods: FB, fastbat electronic pen; VIA, video image analysis; CP, one of the authors using a cellulose acetate grid with unlimited time; CA, chiller assessor, measuring rapidly with a cellulose acetate grid. Table 2. Pearson corr elation coefficients for eye muscle area measurements Measurement FB VIA CP CA SW P a 8 b b a CP 0.943 0.856 1.00 0.937 0.565 -0.250 FB 1.00 0.878 0.943 0.950 0.584 -0.192 VIA 0.878 1.00 0.856 0.864 0.549 -0.231 CA 0.950 0.864 0.937 1.00 0.581 -0.246 SW 0.584 0.549 0.565 0.581 1.00 0.565 P 8 -0.192 -0.231 -0.250 -0.246 0.064 1.00 All correlations significant (P < 0.001). FB, VIA, CP and CA Eye muscle area measurements made by fastbat, video image analysis, one of the authors (grid) and chiller assessor (grid) respectively; SW side weight; P Rump P fat thickness. 8 8 210 Animal Production in Australia 1998 Vol. 22 Table 3. Pearson corr elation coef ficients between eye muscle area measurements and estimated a lean meat yields Measurement FB VIA CP CA SW P 8 ELMY ELMY ELMY ELMY ELMY a b b ELMY 0 ELMY 0.717 0.685 0.717 0.729 0.873 -0.414 0.992 1.00 0.996 0.998 0.999 1 ELMY 0.708 0.719 0.713 0.725 0.867 -0.419 0.989 0.996 1.00 0.995 0.996 2 ELMY 0.708 0.682 0.727 0.727 0.868 -0.422 0.992 0.998 0.995 1.00 0.998 3 ELMY 0.708 0.683 0.716 0.737 0.869 -0.421 0.992 0.999 0.996 0.998 1.00 4 0 1 2 3 4 0.622 0.609 0.633 0.645 0.870 -0.436 1.00 0.992 0.989 0.992 0.992 All correlations significant (P< 0.001) FB, VIA, CP and CA: eye muscle area of the authors (grid) and chiller assessor estimated lean meat yield using carcase yield using carcase weight, fat thickness respectively. measurements made by respectively fastbat, video image analysis, one (grid); SW, side weight; P , rump P fat thickness; ELMY , 8 8 0 weight and fat thickness; ELMY to ELMY , estimated lean meat 1 4 and eye muscle area 1 to 4, measured by FB, VIA, CP and VA DISCUSSION Observations and conclusions from this study are tempered by two facts. Lean meat yield was determined by calculation, not by anatomical dissection, and the eye muscle area measurements do not indicate which was the most precise method. In relation to the latter, however, the authors are confident that their grid measurements, made carefully without regard to time, are relatively accurate. They believe that there were no areas of 118 cm2 or 116 cm2 which were recorded by video image analysis and the chiller assessor, respectively. Although lean meat was estimated, this study does provide some legitimate comparative observations. Relative to the areas measured by the other three methods, the chiller assessor (CA) mean for the 100 carcases was non-significantly greater. Video image analysis measurements had a higher standard deviation than those measured by the other techniques. Side weight, which was correlated highly and equally (0.87) with each estimation of lean meat yield, demonstrated its importance in the quantification of carcase lean. Because all measurements of eye muscle area were highly correlated with each other, and were moderately correlated with estimated lean meat yield, calculated without area, it is likely that area, by whichever method calculated, was of about equal value in the quantification of lean. All estimations of lean meat yield, calculated with their respective area measurement, were very highly correlated with each other and very highly correlated (0.99) with estimated lean meat yield calculated without area. This suggests that all four methods of measuring eye muscle area were of approximately equal value. Furthermore, tests between estimated lean meat yield, calculated without eye muscle area, and yields calculated using area measured by each method, were not significantly different. This means that eye muscle area, measured by any one of the four methods, is unlikely to be of great use in quantifying lean meat yield. Eye muscle area measured by the fastbat, video image analysis, cellulose acetate grid (rapidly) and cellulose acetate grid (time unlimited) were of approximately equal value in carcase studies but none appears to be of great value in quantifying carcase lean. The addition of eye muscle area to measurements in order to determine the yield of meat on a carcase, adds little, and is not recommended for quantification in commercial practice. REFERENCES COLE, J.W., ORME, L.E. and KINCAID, C.M. (1960). J. Anim. Sci. 19, 89-100. GOLL, D.E., HAZEL, L.N. and KLINE, E.A. (1961). J. Anim. Sci. 20, 264-67. JANSEN, J., BECH ANDERSEN, B., BERGSTROM, P.L., BUSK, H., LAGERWEIJ, G. W. and OLDENBROEK, J.K. (1985). Livestock Prod. Sci. 12, 231-40. 211 Animal Production in Australia 1998 Vol. 22 JOHNSON, E.R. (1996). Aust. Vet. J. 73, 233-40. JOHNSON, E.R. and PRIYANTO, R. (1991). Proc. 37th Int. Conf. Meat Sci. Techol., Kulmbach, Germany, p. 123. 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