Abstract:

The relationship between marbling (fat) and muscle (protein plus some fat) is generally antagonistic in beef cattle. Both traits are key components of breeding objectives with marbling determining meat quality aspects while muscle, particularly loin eye muscle area (EMA), has implications for yield especially of high value cuts. However, this antagonistic relationship does not appear to hold true in highly marbled carcasses, with high levels of marbling (intramuscular fat, IMF) pushing muscle fibre bundles apart and increasing EMA. The genetic correlation between IMF and EMA, measured using Meat Image Japan camera technology, was 0.23. Lean muscle area, calculated as EMA/(1-IMF), had a genetic correlation of -0.48 with IMF, which is more aligned to expectation from lower marbling breeds. In conclusion, caution is advised when including EMA breeding values in the breeding objectives of highly marbled animals as it is a function of IMF in addition to muscling.