Marbling is the visible form of intramuscular fat (IMF) which appears as fine flecks within the muscle. The presence of marbling has a very positive effect on the eating quality of beef in terms of tenderness, juiciness and flavour.
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 carcass grading using the scoring range 0 to 9 below, and is therefore a subjective measure. In addition to the quantity, the distribution and texture of visible fat flecks within the ribeye are considered during assessment of marbling score.
More precisely, intramuscular fat may be measured by chemical extraction of lipid from a thin facing of the exposed ribeye muscle. Therefore, percent intramuscular fat is an objective measurement that quantifies the total fat content within the ribeye muscle. Percentage intramuscular fat may also be measured objectively using the digital camera technology developed at the Obihiro University, Hokkaido, Japan and used by AWA in its research.
Wagyu Fullblood 100% has the highest propensity to marble of any beef breed. Through its higher marbling, Wagyu beef possesses a higher proportion of monounsaturated fat, compared to other beef. According to Tim Crowe, Ph.D., senior lecturer of nutrition at the School of Exercise and Nutrition Sciences at Deakin University in Australia, the Monounsaturated Fatty Acid to Saturated Fatty Acid ratio runs up to three times higher in Wagyu beef than other beef. Crowe says half of all marbling in a Wagyu carcass is comprised of monounsaturated fats. Because of its beneficial fatty acid profile, Wagyu beef can be eaten in place of other varieties of red meat within the context of overall red meat intake recommendations as part of a healthy and balanced diet.
Marbling potential is determined by both genetics and nutrition. While Wagyu will develop considerable marbling from quality grass feeding, most are feedlot fed on carefully designed rations of straw for roughage and grain for protein and carbohydrates. In Australia Wagyu Fullblood are fed for 400 – 650 days with the aim of producing Marble Score 8+, achieving carcase weights of 300 – 450 kgs and Marble Score 4 to 9+ or 15% to 60% intramuscular fat.
Crossbred Wagyu are fed for 350 – 450 days with the objective of producing Marble Score 5 – 7+, achieving similar carcase weights as Fullbloods but with much greater marbling variability.
EBVs for IMF (intramuscular fat) may be used to select Wagyu Fullblood and Purebred males and females to improve marbling levels.