Plants and animals material contain a group of substances insoluble in
water but soluble in ether, chloroform and benzene, which are commonly called
Like carbohydrates the fats contain carbon, hydrogen, oxygen but in the
first two elements (C and H) are present more in fats.
Primary sources of fatty acids for
Mobilization from cellular stores
LIPID DIGESTIONThere is no enzyme in the saliva capable of attacking
In the case of ruminants, microbial lipase break down fats into
fatty acids which are subsequently hydrogenated (converted from unsaturated
fatty acid to saturated fatty acids)
Whereas in the case of monogastrics, warming, softening, dispersion
and mechanical separation of lipids from the other nutrients occurs in the
The small size of fat particles allow for greater surface exposure to
pancreatic and intestinal lipases, which absorb on the particle surface and
attack fatty acids resulting in
hydrolysis of triglycerides to b-monoglycerides and free fatty acids
Free fatty acids then combine with salt-phospholipids – cholesterol
micelles to from mixed micelles for efficient absorption.
Digestibility of fatty acid decreases when the length of carbon chain
A coarse fat emulsion enters the duodenum, which is the site of the
major process of fat digestion and absorption.
Emulsification of fat occurs in the small intestine after contact with
bile salts – sodium glycocholate and sodium taurocholate. This process reduces the lipid particle size
to 500-1000 Ao (500-1000mm diameters).
The bile salts form aggregates called micelles where the polar or water
soluble portion is towards the periphery and the inner core comprises of the
apolar or water insoluble fraction.
METABOLISMFatty acids must be activated in the cytoplasm before
being oxidized in the mitochondria.
Activation is catalyzed by fatty acyl-CoA
The net result of this activation process is the
consumption of ATP.
Fatty acid + ATP + CoA ——-> Acyl- CoA +
PPi + AMP
Oxidation of fatty acids occurs in the
The transport of fatty acyl-CoA into the mitochondria is
accomplished via an acyl-carnitine intermediateThe process of fatty acid
oxidation is termed b-oxidation since it occurs through the sequential removal
of 2-carbon units by oxidation at the b-carbon position of the fatty acyl-CoA
Each round of b-oxidation produces one mole of
NADH, one mole of FADH2 and one mole of acetyl-CoA.
The acetyl-CoA— the end product of each round
of b-oxidation— then enters the TCA cycle, where it is further oxidized to
CO2 with the concomitant generation of three moles of NADH, one mole of FADH2
and one mole of ATP.
The NADH and FADH2 generated during the fat
oxidation and acetyl-CoA oxidation in the TCA cycle then can enter the
respiratory pathway for the production of ATP.
During high rates of fatty acid oxidation,
primarily in the liver, large amounts of acetyl-CoA are generated.
These exceed the capacity of the TCA cycle, and
result is the synthesis of ketone bodies, or ketogenesis.
The ketone bodies are
Mobilization of Adipose Fatty Acids
• During fasting or starvation, stored fuel needs to be
• the body secretes hormones such as epinephrine and
• These hormones release the second messenger cAMP
• HSL hydrolyzes stored TG to release FA.
• The mobilized fatty acids are released into the
bloodstream where they associate with albumin and cirulate to various tissues
in need of fuel.
Ketotic cows often have low blood glucose (blood sugar) concentrations.
When large amounts of body fat are utilized as an energy source to
support milk production, fat is sometimes mobilized faster than the liver can
properly metabolize it.
If this situation occurs, ketone production exceeds ketone utilization
by the cow, and ketosis results.
Dairy cattle normally produce ketones at low levels for use as energy
It is only when ketone production exceeds demand that problems arise and
Ketosis is important because it decreases feed intake in affected cows
and greatly increases the risk of other diseases.
Prevention is by feeding niacin in ration of cows prior to calving at
the rate of 6-10 grams/head/day.
Feed glucose precursors. Glucose precursors should increase glucose
production by the liver, thereby reducing the need to mobilize body fat to meet
The two commonly available glucose precursors are propionate, in the
form of Ca+ propionate and propylene glycol
Fatty liver in cattle.
v Increase in triacylglcerol in hepatocytes