The use of real-time, linear array ultrasound techniques to predict final carcass composition in beef cattle
Perkins, Thomas Lee
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Recent technological advances have increased the interest in using ultrasonic imaging technology for estimation of carcass composition in the livestock industry. The objectives of this research were: (1) to determine the accuracy of 12th rib ultrasonic measures of subcutaneous fat thickness, longissimus muscle area and intermuscular fat as indicators of carcass composition in beef cattle; (2) to determine the effect of technician on the capture and interpretation of 12th rib ultrasonic images of external fat thickness, longissimus muscle area and intermuscular fat as indicators of carcass composition in beef cattle; and (3) to develop alternative sites of ultrasonic measure which serve as indicators of yield and quality differences in beef cattle. Crossbred feedlot cattle (n = 646) were ultrasonically measured with an Aloka 210Dx, split screen ultrasound unit at the 12th rib interface to evaluate the accuracy of ultrasonic measurements of fat thickness and longissimus muscle area for prediction of actual carcass measures. Average actual differences between ultrasonic and carcass measures of fat thickness and longissimus muscle area indicated that underprediction occurred more often than overprediction for both measures. Correlation coefficients between ultrasonic and carcass measures were .75 (P < .01) for fat thickness and .60 (P < .01) for longissimus muscle. Feedlot steers (n = 36) representing four breedtypes (Brown Swiss, Average Mexican, Rough Mexican and typical British crossbred) were isonified to estimate accuracy and repeatability of fat thickness and longissimus muscle area. Repeated measures of fat thickness and longissimus muscle area were taken by two technicians on 2 consecutive days with an Aloka 500V non-split screen ultrasound unit equipped with a new prototype transducer. Pooled simple correlation coefficients (P < .01) were .87 and .86 for fat thickness and .76 and .82 for longissimus muscle area for technician 1 and 2, respectively. Repeatabilities estimated by intraclass correlation methods were .91 and .81 for images repeated over days and .95 and .83 for images repeated over technicians for fat thickness and longissimus muscle area, respectively. Repeatability estimates of longissimus muscle area interpretation from videotape were .86 within technician -and .76 between technicians. Ultrasonic measurements of 12th rib intermuscular fatness and body wall thickness were not satisfactory predictors of yield and quality grade. Hereford feedlot steers (n = 276) were isonified to evaluate the ability of ultrasonic ellipse measurements of the longissimus muscle area at the 12th rib and fat depth on the rump to predict yield and quality grade. Ultrasonic rump fat was a moderate estimator and ellipse a low estimator of yield grade. However, neither measure was an adequate predictor of quality grade. This research indicates that ultrasonic measures of fat thickness and longissimus muscle area are accurate predictors of carcass composition but further refinement of alternative sites are needed for optimum estimation of yield and quality grade factors in beef cattle.