Serial Measurements Using Real-Time Ultrasound to Evaluate Relative Changes in Fat Thickness and Ribeye Area of Feedlot Steers

Abstract

Feedlot steers representing two breed-X groups (Salers-X, n = 46 and Brangus-X, n = 50) were measured ultrasonically at 28 d intervals to evaluate changes in fat thickness (FTU1), and area of the longissimus muscle (REAU1) for tbe possible development of prediction equations for time and weight effects on ultrasonic measurements. The Salers-X group was also measured (FTU2 and REAU2) with an additional ultrasound unit. Individual ages were not available on the cattle studied, so date of measurement was used as the time effect. Body weights were taken at time of isonification. Initial weight means were 649.5 and 798.3 (pooled SE = 61.1) lb for Salers-X and Brangus-X groups, while final weights were 1093 and 1087.9 (pooled SE = 81.3) lb, respectively. Regression equations for the Salers-X group indicated linear relationships (P < .01) between FTUI for both time and weight effects. Regression coefficients, b (and R2 values) for the Salers-X group were: b = .00045 (.51), b =-.0000079 (.57) for FTUI on weight and time, respectively. For the Brangus-X group, linear relationships existed (P < .01) between REAU1 on weight and time, respectively; b=.0091 (.51) and b=-.OOOI2 (.36). For the Salers-X group, correlation coefficients between the two machines ranged from .802 to .928 for FTU and .361 to .738 for REAU. These data could be useful for development of adjustment procedures of ultrasonic measurements for prediction of carcass merit.