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Ultrasound intramuscular fat
Phenotype
Percentage of intramuscular fat (% IMF) is correlated with USDA marbling score. A minimum of four independent images should be collected and the resulting % IMF predictions averaged for this trait. The % IMF measurement is made from an image that is 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.
Adjusted Value
Percentage of intramuscular fat is adjusted to a common age (e.g., 365 days of age) and in multi-breed settings is also adjusted for breed composition.
Contemporary Grouping
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.
Genetic Evaluation
Given the ultrasound measure of back fat is an indicator of the economically relevant trait of carcass back fat, it is generally included in multi-trait models that include carcass back fat and potentially other carcass fat related traits (e.g., percentage of intramuscular fat, marbling). There are no maternal effects fitted for ultrasound or carcass traits given the maternal influence declines post-weaning.
