Biological determinants of intramuscular fat deposition in beef cattle: Current mechanistic knowledge and sources of variation

Summary

Marbling is a beef quality trait that is loaded with contradictions. On one hand, Australian beef is considered by some in the Japanese markets to have too little marbling. On the other hand, Australian domestic consumers avoid beef that has too much marbling, because they don't want saturated fats in their diets. In the abattoir, meat graders value carcasses that contain some marbling more highly, based on the understanding that eating quality is improved by marbling. And at the feedlot, producers seek animals that can marble without becoming overfat (and thus expensive to feed). These contradictions taken together, explain why Australian beef cattle producers would like to have better control over marbling in their cattle. In part because of the above market contradictions with respect to dietary fat, but also because of the multifaceted nature of the biology of intramuscular fat animal science has made relatively slow progress towards understanding marbling.

Consequently there has been only limited progress toward development of technologies to increase the incidence of marbling and reduce its variation. Historically, considerable work has been committed to definition of nutritional strategies that could increase the age-dependent development of marbling in cattle of generally poorly defined genotype. A significant proportion of this work has been difficult to evaluate due to the interacting effects of genotype and environment (nutrition, temperature, disease) on development of fat deposition in beef cattle.

This project was commissioned to establish an overview of this field of research and from this overview develop a framework for future research. What is marbling? Marbling is the accumulation of fat in meat. It becomes visible to the naked eye once a beef carcass has been chilled, because fat molecules become opaque. The visible deposits of fat are really accumulations of adipocytes (fat cells) and when examined with a microscope, smaller groups of fat cells and droplets also exist, that won't necessarily be easily visible. These small deposits correspond to the snow-flake marbling that is valued highly within some markets and hence by beef graders. Abundant marbling is highly valued by Japanese consumers and actively avoided by Australian domestic consumers. Consistent and abundant marbling are goals for many Australian cattle production enterprises and considerable expense is directed towards achieving them. Likewise considerable research effort has been expended on understanding the trait and maximising the efficiency of producing it.

This review collected, and evaluated past research into the biology that underlies deposition of fat within muscle. A team of six brought their knowledge together to try to understand what has been discovered in cattle and other mammals, and to integrate it into a series of recommendations for future research into the trait in cattle. The review encompasses quantitative and molecular genetics, molecular biology, developmental biology and physiology as well as nutrient biochemistry and disease effects. The release of the review to MLA will be followed by its presentation for publication in a reputable scientific journal. The findings of the review team should assist MLA in setting medium to long-term goals for a program of research into marbling. To this end, a series of recommendations for R&D activities, which will improve the understanding of the biological basis of marbling and its application within the beef industry, are provided.