Marbling is the intramuscular fat (IMF) flecked through the beef, which gives the eating quality greater tenderness, juiciness and flavour and the Wagyu eating experience that consumers expect.

The marbling score is a component of the AUS-MEAT beef quality grading system, and refers to visible fat found between muscle fibre bundles and is assessed within the ribeye muscle. Marbling score is assessed visually by an AUS-MEAT qualified grader during the process of carcase grading using the scoring range 0 to 9 as shown below.

Marbling in Wagyu beef is as much about nutrition as it is about genetics. For breeding, producers look for animals that have a high potential for marbling to breed from. Nutrition from pregnancy through to carcase is designed to give the best possible outcomes for the cow and the calf for whole of life, ensuring the necessary roughage, protein and energy are present in their diet.

Reference