Evaluation of ultrasound measurements of fat thickness and longissimus muscle area in feedlot cattle: Assessment of accuracy and repeatability

Data from two cattle feeding trials were used to estimate accuracy and repe atability of ultrasound measurements of 12-13th rib fat thickness and longi ssimus muscle area. In each trial, images from the last scan prior to slaug hter were interpreted by two certified technicians. Each technician interpr eted the image of each steer twice on two different days. Overall technicia n biases for ultrasound measurements of fat thickness and longissimus muscl e area were -0.17 cm and 0.63 cm(2), respectively. Mean bias in measurement of fat thickness by the two technicians was similar in amount and directio n (-0.14 cm vs. -0.20 cm); however, bias in the measurement of longissimus muscle area by the two technicians took an opposite direction (-1.28 cm(2) vs. 2.54 cm(2)). Repeatability of ultrasound-measured fat thickness was the same for both technicians (0.96 to 0.97). However, measurements of technic ian A showed a better repeatability (0.92) than technician B (0.79) for ult rasound-measured longissimus muscle area. Generally, except for minor diffe rences, degree of experience did not show a consistent difference in the ac curacy of ultrasound estimation of fat thickness and longissimus muscle are a. Hence, it was concluded that technicians could easily be trained to make accurate predictions of fat thickness and longissimus muscle area.