Ultrasound intramuscular fat
Percentage of intramuscular fat (% IMF) is correlated with USDA marbling score. A minimum of four independent images should be collected, and the resulting % IMF measurement is the average of the images. The % IMF measurement is made from images that are collected across the 11th-13th ribs (or 12th-13th ribs) at a lateral position from the animal’s midline, at a point three fourths of the distance from the medial end of the longissimus dorsi muscle. Ultrasound technicians and image processing labs should be certified or accredited by the Ultrasound Guidelines Council.
Percentage of intramuscular fat is adjusted to a common age (e.g., 365 days of age), and in multiple-breed settings is also adjusted for breed composition.
Animals of the same sex, reared and managed together up until the time of scanning form a contemporary group. Scanning contemporary group definition includes the following: herd code, weaning date, weaning management group (pasture, creep, non-creep, etc.), scanning date, and post-weaning management group designation. For animals scanned at a central test, the contemporary group definition for an animal should include its herd of origin and other birth and weaning contemporary group information.
Given the ultrasound measure is an indicator of the economically relevant trait of carcass marbling, it is generally included in multiple-trait models that include carcass marbling and potentially other carcass-fat-related traits (e.g., back fat). There are no maternal effects fitted for ultrasound or carcass traits given the maternal influence declines post-weaning.
Most organizations publish only the marbling EPD and not an IMF EPD because IMF is not an ERT.