Importance of Selection for Fine Marbling
Marbling is a driving force in beef quality and pricing around the world. Our typical thought process in the early days of Wagyu breeding was the more marbling, the better. However, with more research and technological developments we now know fine marbling is superior to course marbling in terms of healthiness and palatability even at similar marbling levels that exceed 50% intramuscular fat (Asa et al., 2017). Below is an image from the Asa et al., 2017 paper that illustrates high level marbled beef with differences in marbling fineness. Carcasses A & D exhibit finer marbling than B & C.
According to Motoyama et al., 2016, fine marbled beef is significantly higher palatable. Additionally, consumers do not prefer beef with a high degree of coarse marbling, especially in heavily-marbled beef. Also stated is consumers in Japan and Korea tend to prefer evenly distributed marbling in beef which is typically priced higher.
Compared to course marbling, fine marbling has a more preferable lipid profile. Fine marbling melts at lower temperatures due to more oleic acid content. In fact, the most desirable marbling (i.e., with the lowest melting point) melts at a temperature less than the normal body temperature of cattle (101F or 38C). This means it exist in an oily state rather than solid state inside the muscles and virtually undetectable by conventional ultrasound. Course marbling is chunky and requires higher temperature to melt due to higher saturated fat content.
I served on the Ph.D. committee of now Dr. Jose Valenzuela at Murdoch University in Western Australia. His dissertation was characterizing how marbling invades the muscle in Wagyu cattle by monitoring histology and melting temperature. His research concluded that marbling is invasive, hyperplastic and hypertrophic. This differs from simple accumulation by adipogenesis. As the melting point of marbling decreases, the invasiveness becomes more aggressive. The invading adipocytes typically degenerate the muscle fibers from contact. This shows similarities to human muscular dystrophy (Valenzuela et al., 2020).
Okay…..so how do we select and feed for finer marbling? Short answer: genetics, days on feed and feed ingredients. Lloyd et al., 2017 show that low melting point is heritable and present data on a couple sires. Dr. Sally also presents data that show melting temperature of marbling lowers with more days on feed in both Black Wagyu and Akaushi.
Carcass cameras have the ability to objectively score marbling fineness. This is the easiest way to capture data to use in your selection criteria. AuWA has an EBV for fineness that producers can use. Personally, I have been visually observing marbling texture for around 10 years mainly to select against course marbling. The courser marbled steaks seemed more grizzle-ly and tasted like the outside fat/backfat. I also have been trying to compare marbling quality to other eating characteristics like mouth coating and juiciness, etc. We still have much to learn and I credit the Japanese for being the first to measure and select for higher oleic acid content and marbling fineness. This has paved the way for us to look further into improving our craft.
Asa, R., M. Okamoto, K. Sasaki, M. Ooi, K. Hagiya, and K. Kuchida. 2017. Relationship between the finesness of marbling and sensory evaluation in Japanese Black cattle. Nihon Chikusan Gakkaiho. 88(2): 139-143.
Lloyd, S., J. Valenzuela, E. Steele, and R. Dawkins. 2017. Genetics of marbling in wagyu revealed by the melting temperature of intramuscular and subcutaneous lipids. Int. J. Food Sci.
Motoyama, M., K. Sasaki, and A. Watanabe. 2016. Wagyu and the factors contributing to its beef quality: A Japanese industry overview. Meat Science, 120(2016), 10-18.
Valenzuela, J., S. Lloyd, F. Mastaglia and R. Dawkins. 2020. Adipose invasion of muscle in Wagyu cattle: Monitoring by histology and melting temperature. Meat Science, 163.
