Lipids are a concentrated source of energy found in feed for dairy cows. They consist primarily of triglycerides made of glycerol bonded to three fatty acid chains. In the rumen, lipids are hydrolyzed into glycerol and fatty acids. Microbes hydrogenate unsaturated fatty acids. Excess lipids can inhibit fiber digestion. Hydrolyzed fatty acids pass through the small intestine where they are absorbed and transported to tissues as chylomicrons. Around 50% of milk fat comes from fatty acids absorbed from the intestine. The liver plays a role in metabolizing fatty acids, either using them for energy or converting excess amounts to ketones. Adding lipids to dairy rations in moderate amounts can increase energy

1. LIPID METABOLISM
UMAR HAYAT

2. TYPES OF LIPIDS
• Lipids are water insoluble, soluble in organic solvents (ether, chloroform,
hexane, etc.). Concentrated source of energy in feed. Usually, the diet of
cows contains only 2 to 4% lipids. Important for dairy cows, directly
contribute 50% to milk fat.
• Oilseeds contain more than 20% lipids. Oil from oilseeds can be hsed
unextracted in diets of cows. Only small amounts of lipids are found in
forage and seed.
• Triglycerides are found primarily in cereal grains, oilseeds and animal fats.
The basic structure of triglycerides consist of one unit of glycerol (a 3
carbon sugar) and three units of fatty acids.
• Glycolipids form a second class of lipids found in forage. Structure similar
to the triglycerides except that one of the three fatty acid has been
replaced by a sugar (usually galactose).

3. TYPES OF LIPIDS
• When one of the fatty acids is replaced by a phosphate bound
to another complex structure the lipid is referred to as
phospholipid. Phospholipids generally found in ruminal
bacteria.
• Melting point is influenced by the degree of saturation and to a
lesser extent by the length of the carbon chain.
• Plant lipids typically contain 70 to 80% unsaturated fatty acids
and they tend to remain in the liquid state (oils). Common fatty
acids found in plant lipids range from 14 to 18 carbons.
• Animal fats contain 40 to 50% saturated fatty acids and remain
in the solid state (fats). The degree of unsaturation affects
digestion by animal.
• It interferes with the fermentation of carbohydrates in the
rumen.

4. Common fatty acids in dairy cows diet
Common Name
Structure Abbreviation
Melting point (°C
................................................ Saturated acids ......................................................
Myristic CH3-(CH2)12-COOH (C14:0)
54
Palmitic CH3-(CH2)14-COOH (C16:0)
63
Stearic CH3-(CH2)16-COOH (C18:0)
70
.............................................. Unsaturated acids ............................
Palmitoleic
CH3-(CH2)5-CH=CH-(CH2)7-COOH (C16:1)
61
Oleic
CH3-(CH2)7-CH=CH-(CH2)7-COOH (C18:1)
13
Linoleic CH3-(CH2)4-CH=CH-CH2-CH=CH-(CH2)7-COOH (C18:2)
-5
Linolenic CH3-CH2-CH=CH-CH2-CH=CH-CH2-CH=CH-(CH2)7-COOH (C18:3)
-11
* The first number denotes the total number of carbons and the second number
denotes the number of double bonds in the molecule.

5. HYDROLYSIS AND SATURATION OF LIPIDS IN
THE RUMEN
• Lipids hydrolysis in the rumen: bonds between
the glycerol and the fatty acids broken down
to produce glycerol and three FAs.
• Glycerol fermentation to VFAs. Some FAs used
by bacteria for the synthesis of phospholipids
for build cell membranes.
• Ruminal microbes hydrogenate unsaturated
fatty acids. Fatty acid becomes saturated.

6. LIPIDS IN THE RUMEN

7. • Excess lipids in the diet (> 8%) have negative effect
on milk yield and fat % in the milk. Unsaturated have
more negative effect than saturated.
• FFAs in rumen attach to feed /microbial particles and
impede fibre fermentation.
• Protected Lipids slow down hydrolysis, make them
"inert“ . The seed coat protects lipids, less ruminal
hydrolysis.

8. • Industrial treatments involve the formation of
soaps (calcium salts) make FAs insoluble and
inert in the rumen.
• Microbial phospholipids 10 to 15% of the
lipids leaving the rumen, Saturated FAs 85 to
90% (bound to feed and microbial particles).
• Microbial phospholipids in the small intestine
make fatty acids pool and mix with bile and
pancreatic juice (enzymes +bicarbonate.

9. INTESTINAL ABSORPTION OF LIPIDS
• These secretions are essential to prepare the lipids for absorption by
forming water miscible particles called micelles that can enter the
intestinal cells.
• In the intestinal cells, fatty acids bound to glycerol to form triglycerides.
Triglycerides +free fatty acids+ cholesterol coated with protein form
triglyceride-rich lipoproteins (TG-rich LP) called chylomicrons / very low
density lipoproteins.
• The TG-rich LP enter lymph vessels and flow to the thoracic duct , enter
the blood system.
• In contrast to most nutrients absorbed from the gastro intestinal tract, the
absorbed lipids enter the general circulation directly and are used by all
body tissues without a preliminary processing by the liver.

12. UTILIZATION OF DIETARY LIPIDS BY
THE UDDER
• About 50% of milk fat derived from the uptake of fatty
acids by the mammary gland. Triglyceride-rich
lipoproteins during the intestinal absorption of lipids
provide the FAs.
• More long chain fatty acids (LCFAs, C > 16) in diet result
in their more secretion in milk, but less synthesis of
short- and medium-chain FAs in the mammary tissue.
• Thus, the marked depression in fat secretion when
cows are fed low fiber diets can be compensated only
partially by increasing fat in the diet.

13. THE ROLE OF LIVER AND FAT
MOBILIZATION
o During under feeding or early lactation period, fat mobilized
from adipose tissues to obtain energy in addition to dietary
fat. Fatty acids from the triglycerides stored in the adipose
tissues released into the blood.
o Mobilized fatty acids taken up by the liver , used as energy
source or converted to ketones, released in the blood and
used as energy source by many tissues.
o The liver does not have a high capacity to form and to export
TG-rich LP and the excess mobilized fatty acids are stored as
triglycerides within the liver cells.
o The fat deposited in the liver contributes to development of
metabolic disorders (e.g., ketosis and fatty liver) in early
lactation.

15. ADDED LIPIDS IN DAIRY RATIONS
o Lipids are "cold" nutrients, produce less heat
in the body.
o Several potential benefits:
– Increase energy density of the ration, in high
forage diet;
– Limit need for carbohydrate-rich concentrates
required in early lactation;
– Help to reduce the heat stress of a lactating cow.

17. Animal Response
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•
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Variable feed intake & milk production
responses according to the type of lipids.
Do not feed ore than about 1.5 kg/day of added
fat to dairy cows. Milk production is maximized
when lipids comprise 5% of the dietary dry
matter
Negative effects if fed more than 6%. Decreases
milk protein by about 0.1%. In addition, may
depress feed intake, milk production and milk fat
composition.