Essay About Partitioning Of Fat And Abdominal Cavity

The Partitioning Of Fat In Ruminantscan
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The partitioning of fat in ruminantscan
nutrition be used as a tool to
regulate marbling?
D.W. Pethick1, L. Mclntyre2, G. Tudor3 and J.B. Rowe4
�School of Veterinary Studies, Murdoch University, WA, 6150
*Agriculture Western Australia, South Perth, WA, 6151
3AgricuIture Western Australia, Bunbuty, WA, 6231
4Department An imal Science, University of New England, Armidale, NSW, 2351
Summary
In this paper we propose that regulation of the glucose/
insulin axis by diet will result in increased fattening at
the marbling (intramuscular) depot. The pattern of fat
accretion in the whole carcass is first described to
emphasise that the marbling depot is relatively late
maturing. The pathways of fat metabolism are then
discussed with the aim of examining the possibility of
regulating fat partitioning between depots in ruminants.
The importance of acetate versus glucose + lactate as
substrates for lipogenesis differs between depots in
the ruminant and it is proposed that this might allow for
differential control of lipogenesis. The role of diet in the
manipulation of pathways for lipogenesis in ruminants
is then explored. Both glucose infusion and diets
promoting starch digestion in the small intestine
increase the activity of enzymes (ATP citrate lyase)
associated with lipogenesis from glucose indicating a
greater relative importance of glucose as a lipogenic
substrate and this may have an impact on the relative
growth of different fat depots via the glucose/insulin
axis. Chromium supplementation to ruminants
consuming a diet low in chromium also increases the
relative importance of glucose as a precursor for
lipogenesis and causes redistribution of fat away from
the subcutaneous site. Finally the effects of feeding
different cereal grains and chromium supplementation
to 150 day fed steers on visual marbling score are
discussed. It is concluded that starch digestion in the
small intestine is associated with increased visual
marbling score.
Introduction
Consumer preferences and the need to maximise
profitability in the rural sector have resulted in an
enormous research effort to maximise muscle and
minimise fat in meat producing animals such as pigs,
sheep and cattle. However, leanness at all sites is not
always desirable and some markets will pay a premium
for beef meat containing extra levels of fat (marbling). In
this review we first discuss the development of fat tissue
during growth and how this relates to consumer
preferences. We then examine the biochemical pathways
for lipogenesis in ruminants and discuss dietary
mechanisms for regulating these pathways. Finally, the
possibility for altering the distribution of fat between
depots in ruminants is explored with particular emphasis
on marbling.
Growth of adipose tissuepractical
aspects
Adipose tissue is deposited in specific depots which
are similar for all mammals. The primary depots are within
the abdominal cavity (perirenal, mesenteric and
omental), intermuscular, subcutaneous and
intramuscular. However, the proportions differ between
the species and are influenced by age. Thus the pig has
more subcutaneous fat (70% of total body fat) and less
abdominal fat than sheep and beef cattle (Wood, 1984).
Adipose tissue depots are thought to develop in
the order of abdominal, intermuscular, subcutaneous
and finally intramuscular (Vernon, 198 1). The
progressive development of some fat depots in cattle is
shown in Figure 1. The data suggest that abdominal fat
changes largely in line with carcass (or body) weight
while all other depots increase relative to carcass weight.
Thompson et al. (1987) measured chemical fat content
at all sites in mature Merino sheep and found
intramuscular fat was 7% of total body fat. This
compared with subcutaneous at 24%, intermuscular
20%, kidney fat 1 1%, omental fat 16% and mesenteric at
6%. Therefore the marbling depot is of moderate to small
size.
Beef produced for the Australian domestic market
originates from cattle yielding a carcass weight of about