PSIV-A-5 - Comparison of Left vs Right Body Composition Endpoints in Beef Cattle Using Carcass Ultrasound

Abstract: Feedlot cattle (n = 50) were ultrasounded to compare ultrasound vs carcass measurements, and to test the hypothesis that the left and right side of an individual animal are not statistically different during the Ultrasound Guidelines Council (UGC) Carcass Certification live animal exam at West Texas A&M University (WTAMU). Cattle (steers, heifers and bulls) represented a variation in breed types. A UGC certified technician scanned the cattle at the WTAMU Research Feedlot on their right side. The following day, the same technician scanned animals on the left side. Carcass ultrasound measurements included 12-13^th ribeye area (REAU), subcutaneous fat thickness (FTU), intramuscular fat percentage (IMFU) and rump fat thickness (RFU). Carcass measures included 12-13^th ribeye area (REAC) and fat thickness (FTC) along with marbling score (MS). Correlations between REAC and REAU were 0.83 for the left side and 0.80 for the right side, correlations between REAC left vs right were 0.94 and REAU left vs right were 0.77 (P < 0.01). A minor difference (2.27 cm²) in left vs right sides of REAC (P = 0.04) was detected. A larger difference (4.03 cm²) in left vs right REAU (P < 0.01) was noted; REAC right vs REAU right also differed (P < 0.01) by 8.13 cm² with REAU being larger. No differences were observed between FTC left vs right (P = 0.26), FTU left vs right (P = 0.94) or FTC right vs FTU right (P = 0.15). A difference was detected between the FTC left and FTU left (P = 0.01). Correlations between REAU/REAC, FTU/FTC, and IMFU/IMFC were all significant (P < 0.05). These data present strong correlations between ultrasound and carcass traits, as well as the point that one side of an animal should be scanned as opposed to another side.