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LETTERS TO THE EDITOR |
Department of Animal Sciences, Colorado State University, Fort Collins, CO 80523-1171, email: Keith.Belk{at}ColoState.edu
The objectives of our study were to determine whether the Computer Vision System (CVS) could: 1) predict differences in fabricated yields in beef carcasses and 2) augment the application of USDA Yield Grades to beef carcasses. Our study did not presume to evaluate all other possible methods of predicting beef carcass composition, including the use of other mechanical or ultrasonic measures of fat thickness. In fact, "mechanical or ultrasonic fat thickness measurements" from "several critical points" would most likely not be allowed for use in assignment of USDA Yield Grades given current Official U. S. Standards for Grades of Carcass Beef because such methodology would deviate from the regulated methods for assessing fatness. Furthermore, use of invasive fat measurement probes would clearly prove to be a food safety concern.
Manufacturers of carcass assessment instrumentation have determined that evaluation of beef carcasses using ultrasonic scanning technology (e.g., SFK AutoFom) is not effective in predicting beef carcass yields, or that such measures are not logistically possible, and have therefore not initiated commercial marketing campaigns for such technologies, even though similar instruments are marketed for use by the pork industry. Because video-imaging technology was considered ready for commercial testing, and because it was ranked first for research funding by the National Beef Instrument Assessment Planning Symposium (NLSMB, 1994
), our efforts in this article focused on research needs identified by the beef industry.
We fail to see how another type of mechanical or ultrasonic evaluation system would simplify or speed up the carcass evaluation process; CVS can evaluate and report all the necessary measures to the USDA grader in much less than 1 s, and can do this with greater carcass-to-carcass and plant-to-plant repeatability than traditional methods. Based on the computations by M. L. Thonney, the instrument augmentation system proposed in Table 5 of our study (which includes the independent variables of hot carcass weight [HCWT], CVS-determined longissimus muscle area [CVSREA], and adjusted fat thickness [ADJFAT]) would clearly provide producers with the best estimate of carcass fabrication yields and impart the greatest confidence when used to valuate carcasses, while also addressing the stated concerns related to inclusion of kidney, pelvic and heart (KPH) fat in the prediction equation. Our manuscript clearly acknowledged that ADJFAT was the single most important carcass assessment factor in the prediction of carcass fabrication yields.
Although subcutaneous fat measurements usually have the highest partial r2 when used in prediction equations to forecast carcass cutability, we do not agree that "subcutaneous fat thickness is the most logical predictor of wholesale cut yield" as a "single predictor." This is because 1) a single linear measurement of subcutaneous fat thickness must be "adjusted" by the evaluator to adequately reflect differences in carcass fat distribution and, thus, carcass fatness, according to current Official U. S. Standards for Grades of Carcass Beef, and 2) it does not adequately account for variation in muscle:bone ratios (e.g., see Cross et al., 1973). Hot carcass weight was included in the prediction model of Murphey et al. (1960) because the use of a "two-dimensional" measurement of longissimus muscle area to reflect musculature in predictions of percentage fabrication yields requires a size register; in other words, the effect of longissimus muscle area on the predicted value is constrained by the effects of carcass size in the model. Larger carcasses (including "larger mature-sized" carcasses) have larger longissimus muscles than smaller carcasses, but not necessarily greater muscle:bone ratios. Murphey et al. (1960) did not include carcass weight in the model as an indicator of obesity, and the use of longissimus muscle area by those researchers was not intended to predict the volume (the weight of a "three-dimensional object") of the longissimus muscle. Many studies, including that of Abraham et al. (1980), have repeatedly validated the effectiveness of using ADJFAT, HCWT, longissimus muscle area, and percentage of KPH fat to predict beef carcass fabrication yields. Our study simply reflected an attempt to provide the same information to USDA graders using instrumentation.
Literature Cited
Abraham, H. C., C. E. Murphey, H. R. Cross, G. C. Smith, and W. J. Franks Jr. 1980. Factors affecting beef carcass cutability: An evaluation of the USDA yield grades for beef. J. Anim. Sci. 50:841–851.
Cross, H. R., Z. L. Carpenter, and G. C. Smith. 1973. Equations for estimating boneless retail cut yields from beef carcasses. J. Anim. Sci. 37:1267–1272.
Murphey, C. E., D. K. Hallett, W. E. Tyler, and J. C. Pierce Jr. 1960. Estimating yields of retail cuts from beef carcasses. J. Anim. Sci. 19:1240.
NLSMB. 1994. National Beef Instrument Assessment Plan—1994. National Live Stock and Meat Board, Chicago, IL.
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