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Marbling biology - what do we know about getting fat into muscle?
Conference proceeding   Open access

Marbling biology - what do we know about getting fat into muscle?

David W. Pethick, Greg S. Harper, Jean-François Hocquette and Yong Hong Wang
Proceedings of Australian beef – the leader! The impact of science on the beef industry, pp.103-110
Australian Beef - The leader conference! The impact of science on the beef industry
Australian beef – the leader! The impact of science on the beef industry (University of New England, Armidale, NSW, Australia, 07/03/2006–08/03/2006)
2006
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Abstract

Computer Science Life Sciences
Key findings of research: • Intramuscular fat content (% fat) or marbling score is clearly late maturing. • However fat development within muscle is not late maturing and the expression of marbling is due to maintained fat synthesis in combination with declining muscle growth as animals get older. • A growth curve for the development of marbling is discussed - key concepts include (i) a period up to about 200kg where intramuscular fat does not increase (ii) a period of linear development as carcass weight increases from 200-450kg and (iii) the suggestion that intramuscular fat content reaches a maximum at mature body size (around 500kg carcass weight depending of course on genotype). • Expression of intramuscular fat after extended grain finishing is driven by 3 primary genetic loci (i) overall fatness (ii) the degree of muscle development which also interacts with mature body size and (iii) the extent of fat distribution bias toward the intramuscular site. The interaction of these 3 factors requires further modeling to understand the how these genetic factors (including new gene markers) effect final marble score. • The level of intramuscular fat at the start of finishing is a key determinant of the final level of intramuscular fat after finishing. This raises the feasibility of using ultrasound estimates of intramuscular fat content at the start of finishing as a means of selecting superior marbling animals. • Recent results from Beef CRC research in collaboration with International partners using modern biochemical and genomic tools suggest that (i) intramuscular fat cells are different to other fat depots (i.e. subcutaneous) and (ii) intramuscular fat cell development is determined relatively early in life (3-8 months of age) which is consistent with the conclusions of our growth and development studies. The possibility for control of intramuscular fat development separately from other depots will be explored in the new CRC. • The major nutritional and/or management tool for increasing the development of marbling is to maximise the availability of net energy (and glucose) for fat synthesis during finishing. • Net energy available for fattening is the most likely reason why grain feeding (compared to grass) results in a higher marbling score at equal carcass weights. • In heavier ‘British’ type cattle (LW≥540kg, P8=12mm) it is difficult to increase the net energy for fattening by reducing protein supply (that is these cattle have a low protein requirement) and this is clearly an avenue for reducing feed costs. • Increased processing of the ration (i.e. steam flaking versus dry rolling) will increase the net energy intake and glucose supply and increase marbling. The mechanism is to maximise starch digestion in the rumen (of course within animal health limits) and also the small intestine and so reduce starch loss in the large intestine and faeces.

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