Comparison of Ultrasound and Actual Beef Carcass Measurements as Influenced by Stockering Performance and Finishing System

A total of 216 Angus-crossbred steers (270 ± 19.3) kg were used in a three-year study to assess the effects of winter stocker growth rate and finishing system on beef carcass parameters as measured by ultrasound, a United States Department of Agriculture grader at a commercial slaughter facility, and laboratory analysis. During winter months (December to April) steers were randomly allotted to one three stocker growth rates: low (0.23 kg d-1; LOW), medium (0.45 kg d-1; MED), or high (0.68 kg d-1; HIGH). Upon completion of the winter phase, steers were randomly allotted within each stocker treatment to either a corn silage-concentrate (CONC) or pasture (PAST) finishing system. All steers, regardless of finishing treatment, were finished to an equal-time. Upon completion of the finishing period, steers were ultrasounded to obtain estimates of loin muscle intramuscular fat percent (US-IMF), ribeye area (US-REA), and rib fat (US-RF). Steers were harvested and carcass data collected. Ultrasound-IMF measurement detected a finishing system effect (P<0.0001) but no evident impact of stocker system. Laboratory determined IMF (actual-IMF) resulted in detection of both a stocker treatment and finishing system effect (P<0.05). When actual-IMF and US-IMF were each converted to a USDA quality grade (QG) equivalent, and compared with the USDA grader QG (grader-QG), US-QG and grader-QG over estimated (P<0.05) actual IMF-QG for all treatment subgroups except HIGH-CONC, where US- and actual-QG were in agreement. Grader-QG and actual IMF-QG detected both stockering and finishing treatment effects, while US-QG did not. Our results clearly demonstrate that US-IMF measurement was unable to identify changes in loin muscle IMF deposition due to stockering plane of nutrition, whereas laboratory analysis and the USDA grader could identify changes in loin muscle IMF deposition due to stockering plane of nutrition.