The repeatability of ultrasound image measurements of the longissimus dorsi muscle (AOL) and of the rumpfat (EGG) and backfat (EGL) subcutaneous thickness was evaluated. Ultrasound images taken from the back (between 12th and 13th ribs) and from the rump (between gluteus medium and biceps femoris muscles) of Nelore heifers at 14 and 22 months of age were classified as acceptable, marginal and rejected. The acceptable and marginal images were measured twice by three technicians at different levels of training. It was estimated repeatabilities among and within technicians by class of image quality in order to determine effect of image quality and of the technician at the absolute difference value between the first and second measurement of those traits. The repeatability for acceptable images was higher than for marginal images, for both among and within technicians. Regarding to the absolute difference analyses between the first and second interpretation, the effects of the technician for AOL and EGL and quality class of image for AOL were significant. In general, the repeatability was higher for the most experienced technician. It is advisable that measurements of images in the same contemporaneous group should be done by one single technician.
backfat thickness; beef cattle; image quality; longissimus dorsi muscle area; ultrasound
