The use of real-time ultrasound (RTU) to measure body composition in livestock started in the 1950s. The first publication of researchers attempting to measure body composition in live beef cattle was in 1956. Temple et al. (1956) used a somascope to measure backfat thickness in beef cattle. Thereafter, many other researchers throughout the world started doing research with ultrasound to predict body composition. The first instruments used were called amplitude mode (A-mode), and were capable of measuring fat and muscle depth. The second instruments were called brightness mode (B-mode), and were capable of measuring fat thickness and longissimus muscle area. The third advancement in instrumentation used to measure carcass traits in livestock which is widely used today, was RTU (a form of B-mode). This instrument is capable of measuring subcutaneous fat (SC) thickness, longissimus muscle area, intramuscular fat, internal fat in real time. Real-time ultrasound is a non-invasive technique to measure body composition in live animals and has been used for genetic evaluation, management and research purposes for the past 30 years. Research has shown that it can accurately predict carcass traits in beef cattle (Ribeiro, 2006), swine (Houghton and Tourlington, 1992) and sheep (Ribeiro et al., 2010), internal fat in beef cattle (Ribeiro and Tedeschi, 2012), and BCS in cattle (Gates, 2011), sheep (Carter, 2011) and goats (Duff, 2010). The use of RTU is inexpensive and allows producers to increase speed in genetic selection for terminal traits, estimate days on feed and assess body energy reserves.