LIPID DIGESTION
• References
–
–
–
–
Church: 298-312
Jenkins et al. 2008. JAS 86:397-412
French et al. 2000. JAS 78:2849-2855
McGuire and McGuire. 2000. JAS 77:1-af-8-af
• Lipids in ruminant diets
– Usually a low percentage of the diet, 1-4% of
the DM
• Amounts have been increasing
– Lipids in feeds
Feed
% EE
Corn and
4-20
other seeds
Forages
4-6
Form
Triglycerides
Galactosyl
glyceryl esters
+ pigments
waxes, essential
oils
– Structure
• Triglyceride
O
||
O C-O- C-R
||
|
R-C-O-C
O
|
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C-O-C-R
– 46% oleic acid (18:1) and 42% linoleic acid (18:2)
• Galactosyl diglyceride
O C-O-gal O gal
||
|
R-C-O-C
O
|
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C-O-C-R
– 31-61% linolenic acid (18:3)
– Common fatty acids in ruminant diets
Fatty acid
Myristic
Palmitic
Palmitoleic
Stearic
Oleic
Linoleic
Linolenic
Arachidonic
Eicosapentaenoic
Docosahexaenoic
Carbon:Double Bonds
14:0
16:0
16:1
18:0
18:1
18:2
18:3
20:4
20:5
20:6
Double bond position
Cis-9
Cis-9
Cis-9, 12
Cis-9, 12, 15
Cis-5, 8, 11, 14
Cis-5, 8, 11, 14, 17
Cis-5, 7, 10, 13, 16, 19
– Unsaturated fatty acid isomers
• Cis isomers (Naturally found in feeds)
H
H
\
/
C=C
/
\
C
C
/
\
R
R
• Trans (Found in ruminant meat and milk as well as
hydrogenated oils)
R
\
C
H
\
/
C=C
/
\
H
C
\
R
•
Lipid digestion in the rumen
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•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
alpha-galactosidase
beta-galactosidase
O CH2-O-Gal-Gal
O CH2-O-Gal
O CH2OH
||
|
||
|
||
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R1-C-O-CH2
O
-------------------- R1-C-O-CH2
O --------------------- R1-C-O-CH2
O
|
||
|
||
|
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CH2-O-C-R2
CH2-O-C-R2
CH2-O-C-R2
Galactosyl diglyceride
Lipases
Galactose
|
|
Propionate ------------Glycerol-------Unesterified
FA
(Rn)
O
||
O CH2-O-C-R1
||
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R2-C-O-CH2
O
|
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CH2-O-C-R3
Triglyceride
Lipases
– Lipid hydrolysis
• Two lipases are produced by the bacteria,
Anaerovibrio lipolytica
– One is cell bound
– One is extracellular
• Hydrolysis is a rapid, two-step process
– Slower on a high grain diet
– Intermediates are rapidly metabolized in the rumen
• Factors influencing lipid digestion
– Dry matter intake
» Decreases digestibility
– Amount of fat consumed
» Decreases digestibility
– Fatty acid saturation
» Decreases digestibility
– Fatty acid metabolism
• Minimal absorption or degradation of long
chain fatty acids in the rumen
• Lipids leaving the rumen
– 80-90% are free fatty acids bound to feed particles or
microbes
– 10% leaves as microbial phospholipids
– If not protected, small quantities of undigested fats
may pass
– More fat leaves the rumen than enters
• Long chain fatty acid alterations in the rumen
– Biohydrogenation
– Microbial synthesis of long-chain fatty acids
• Results of long-chain fatty acid metabolism
Fatty acid
Saturated
14:0
16:0
18:0
Unsaturated
16:1
18:1
18:2
18:3
Saturated
14:0
16:0
18.0
Unsaturated
16:1
18:1
18:2
18:2 CLA
18:3
Corn
7.0
2.4
Feed
Barley-SBM-Tallow conc
2.5
32.7
20.6
45.6
45.0
-
.8
25.1
16.5
1.9
Intramuscular fat
Swine
Beef
Barley-SBM-Tallow conc
2.3
27.4
16.0
2.0
23.8
10.6
3.7
45.1
12.8
0.8
4.0
38.6
3.0
0.4
0.7
Grass
4.6
20.8
3.3
2.4
5.7
14.0
49.2
Grass
2.7
22.8
14.7
3.9
40.6
2.1
1.1
1.1
• Biohydrogenation
– Microorganisms
• Primarily bacteria, particularly cellulolytic bacteria
• Protozoa
–
–
–
–
Contain 75% of the microbial fatty acid in rumen
Not actively involved in biohydrogenation
Contains high concentrations of 18:2 CLA
Obtained by ingesting bacteria
• Fungi have capability for biohydrogenation, but make up
a small proportion of the microbial biomass
– Processes
• From Linoleic acid
– High roughage diet
Linoleic acid (cis-9, cis-12 18:2)
cis-9, trans-12 isomerase
from Butyrvibrio fibrisolvens
(Rapid)
Conjugated linoleic acid (CLA, cis-9, trans-11 18:2)
Also called Rumenic acid
cis-9 reductase
from Butyrvibrio fibrisolvens
(Rapid)
Vaccenic acid (trans-11 18:1)
trans-11 reductase
from Clostridium proteoclasticum
(Slow)
Stearic acid (18:0)
– High grain diet (Low pH)
Linoleic acid (cis-9, cis-12 18:2)
trans-9, cis-12 isomerase from
Megasphaera elsdenii, Streptococcus bovis
(Rapid)
Conjugated Linoleic Acid isomer (trans-10, cis-12 18:2)
cis-12 reductase from
Megasphaera elsdenii, Streptococcus bovis
(Rapid)
Trans-10 18:1
trans-10 reductase
(Slow)
Stearic acid (18:0)
• From Linolenic acid
– High roughage diet
Linolenic acid (cis-9, cis-12, cis-15 18:3)
Cis-9, trans-11, cis-15 18:3
Trans-11, cis-15 18:2
Vaccenic acid (trans-11 18:1)
Stearic acid (18:0)
– Why do bacteria reduce unsaturated fatty acids
• Mechanism to use excess hydrogen
• Detoxify unsaturated fatty acids
– Results of biohydrogenation
• High roughage diets
– High concentrations of CLA (cis-9, trans-11 18:2) and
vaccenic acid (trans-11) 18:1 in the rumen
• High concentrate diets
– High concentrations of trans-10, cis-12 18:2 and trans-10
18:1 fatty acids in the rumen
• On all diets
– High concentrations of stearic acid
• These fatty acids will be absorbed in the small intestine
and represent a high proportion of the fatty acids
presented to tissues
– Tissue metabolism of trans isomers of fatty acids
• Conversion of trans-11 18:1 to CLA (cis-9, trans-11 18:2)
– Occurs in mammary gland and adipose
– Major source of CLA (cis-9, trans-11 18:2) in meat
and milk
– Mechanism
9
- desaturase
Trans-11 18:1
CLA (cis-9, trans-11 18:2)
2H
– Other pathways for delta-9 desaturase
» Palmitic acid (16:0)
» Stearic acid (18:0)
Palmitoleic acid (16:1)
Oleic acid (18:1)
– Effects of biohydrogenation of unsaturated fatty
acids in ruminants
• Increased concentrations of saturated fatty acids in meat
and milk
• Increased concentrations of CLA (cis-9, trans-11 18:2) in
ruminant meat and milk
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–
–
–
–
–
Anticarcinogenic
Reduces atherosclerosis
Alter body composition
Diabetes control
Improved immune response
Improved bone mineralization
• Milk fat depression in lactating dairy cows
– trans-10 18:1 produced from linoleic acid in cows fed high
grain diets will directly inhibit long chain fatty acid
synthesis in the mammary gland
• Reduces the vitamin E requirement of ruminants
• Indicates a low essential fatty acid requirement in mature
ruminants
– Microbial synthesis of fatty acids
• Distribution of lipid in the rumen
% of total lipid (Wet digesta)
Bacteria
4.1
Protozoa
15.6
Feed particles in rumen fluid
80.3
• Bacterial synthesis
– C18:0 and C16:0
» From acetate and butyrate
– Long straight-chain, odd-numbered fatty acids
» From propionic acid or valeric acid at the initial step
» Increase in cobalt-deficient animals because vitamin B12
is needed for animals to use propionate for glucose
– Long branched-chain fatty acids
» From branched chain VFAs (Isobutyrate, Isovalerate) at
initial step
» Flavor components in meat and milk
– 15-20% of the bacterial fatty acids are monounsaturated
» Can not synthesis polyunsaturated fatty acids
– Bacterial synthesis increases on low fat, high concentrate
diets
• Lipid digestion in the small intestine
– Mechanism similar to nonruminants
– Ether extract digestibility in small intestine is
lower than in nonruminants
– Saturated fatty acids are better absorbed in
ruminants than nonruminants
– Unsaturated fatty acids are less absorbed in
ruminants than nonruminants
– Mechanism of lipid digestion in small intestine
Unesterfied
fatty acids
Unesterfied
fatty acid
Triglyceride
Pancreatic
lipase
Monoglyceride
Phospholipid
Phospholipase A1
Phospholipase A2
Lysolecithin
Bile salt
Phosphatidylcholine
Phosphatidylethanolamine
Micelles
Absorbed into mucosa
Micelles break up
Fatty acids < 14 C are transported directly in the blood
10% of the 18:0 is desaturated to 18:1
Long chain fatty acids combine with lipoproteins to produce VLDL and
chylomicrons
• Lipid transport in the blood
– Transport from the intestine
• Very low density lipoproteins
– Major transport structure from the small intestine
– Favored by saturated fatty acids
• Chylomicrons
–
–
–
–
Less prevalent than in nonruminants
Smaller than nonruminants
Contain 2x more phospholipid than nonruminants
Free:esterified cholestrol ratio is 4:1 compared to 1:1
for nonruminants
– VLDLs and chylomicrons contain apoprotein-C
• Inhibits liver removal of VLDLs and chylomicrons
• Activates lipoprotein lipase at muscle, adipose, and
mammary tissue
– VLDLs and chylomicrons are very short-lived in
ruminants
• 70% of lipids are on HDL
• 20% of lipids are on LDL
• Liver synthesis of lipoproteins
– Little synthesis of fatty acids in liver and
lipoproteins from intestinal mucosa are not
utilized by liver
– Liver synthesis of triglycerides are dependent on
the concentrations of circulating non-esterified
fatty acids (NEFAS) and glycerol from glucose
• If glucose is limiting glycerol synthesis and fatty acid
oxidation, the NEFAS are oxidized to ketones
– Synthesized triglycerides are incorporated into
VLDL to be transported throughout the body
• Fat depots
– Location
• Subcutaneous
• Inter and intramuscular sites
• Visceral sites
– Fatty acid composition
• General
– 80% of FA are 14:0, 16:0, 18:0, and 18:1
– Small amounts of 18:2 and very little 18:3
– Unsaturated fatty acids will have both cis and trans
isomers
– Odd-numbered chain length fatty acids
– Branched chain fatty acids
• Effects of body location of fatty acid
composition
– Subcutaneous fat has more unsaturated fatty acids
the inter and intramuscular fat which has more than
internal fat
– Most external subcutaneous fat and fat in limbs is
more unsaturated than more internal subcutaneous
fat
• Methods to alter fatty acid composition of
meat and milk
– Increasing the CLA content of meat or milk
• Feeding unsaturated fatty acids
– Dose-dependent
» Excessive amounts may inhibit intake and
digestion
– Greater with polyunsaturated oils than
monounsaturated oils
– Processed oil seeds
» More effective than whole seeds
» Less detrimental than pure oils
– Ca-salts
– Fish oil
• Grazing forages
– More effective than stored forages
– Most effective if forages are immature
• Breed differences
• Seasonal changes in CLA in dairies in NE Iowa
CLA c9, t11
1.40
1.20
% of total fatty acids
Baker
1.00
Bushman
0.80
Cline
Kime
0.60
Langland
0.40
0.20
0.00
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
2003
– Breed differences
Muscle
Adipose
Delta-9 desaturase activity
Wagyu
Holstein
3.3
0.8
132.1
39.5
– Increasing the concentrations of polyunsaturated
fatty acids in meat and milk
• Processes
– Feeding whole oil seeds
– Binding of unsaturated fatty acids with Ca
• Limitations
– Expense
– Undegraded fat in the duodenum may reduce rumen
motility and feed intake
– Ca complexes are unpalatable
– Product quality concerns
• Fat supplementation of ruminant diets
– Amounts
• Added fat should be limited to 3-4% of diet DM
• Since normal diet contains 3% fat, the total dietary fat
should be limited to 6-7% of DM
– Types
• Unprotected oils
– Vegetable oils
» Highly unsaturated
» Expensive
» Most adverse effects on digestion, intake and
milk fat
– Animal fats (Tallow, grease etc.)
» Most commonly added to beef and dairy diets
» More saturated
» Less adverse effects
» Difficult to mix in cold weather
• Whole oil seeds
– Whole soybeans, cottonseed, high oil corn
– Increases proportion of oil escaping ruminal
metabolism
– Less adverse effects than free oils
– Easy to use
– Cost effectiveness
• Ruminally inert fats
– Types
» Ca salts of long chain fatty acids
» Prilled fat (Saturated fat processed in small
spheres)
– Escapes ruminal digestion of fat
– Less adverse effects than free oils
– Will reduce feed intake
– Expensive
» Use only if fat percentage from feed sources is
greater than 5% of the diet dry matter
– Advantages of fat supplementation
• Increase energy concentration of the diet
– Energy content of fats
» Gross energy of tallow is 9.4 Mcal/kg
» Digestible energy of fats = Metabolizable energy
» Little fermentative energy loss
• Can increase dietary energy concentration without
decreasing forage level of diet
– It is essential to maintain adequate forage in the diet
to minimize the negative effect of fat on milk fat
percentage indairy cows
– Also need to maintain adequate levels of nonfiber
carbohydrates (30-40%)
• Fats increase energy without increasing heat increment
• In lactating dairy cows, it may elevate fat test
– Particularly if protected fats are fed
– Milk fat depression may occur after use
• Improved reproduction
– Conception rate may be increased by 17%
– Mechanism
» Increased energy balance
Reduce insulin and increase progesterone
Increases follicle size and number
Reduce prostaglandin F2alpha
Increases persistence of corpus luteum
– Response may not occur if the cows use the
supplemental energy for milk production
• Improved diet characteristics
– Reduce dust
– Increase pellet strength
– Limitations of fat supplementation
• Reduced fiber digestion in the rumen
– Mechanisms
» Physically coating the fiber
» Toxic effects on microbes
» Decreased cation availability
– Free fatty acids are more toxic than triglycerides
• Reduced feed intake
– Mechanisms
» Reduced fiber digestion
» Reduced gut motility
» Reduced palatability
» Oxidation of fat in liver
• Milk fat depresssion
– Mechanisms
» Production of trans fatty acids
» Reduced fiber digestion
• Decreased mineral digestion
– Mechanism
» Formation of soaps with Ca and Mg
• Reduction in milk protein % in dairy cows
– Relationship
Milk protein, % = 101.1-.6381x+.0141x2
where x = total dietary fat, %
– Caused more by increased milk production than a
decrease in protein synthesis
– Approaches to limit negative effects of fat
supplementation
• Effects on intake, digestibility and milk fat
– Method of feeding
» Do not feed greater than 4% supplemental fat
» Feed small amounts several times daily
» Feed fats in total mixed rations (TMRs)
» Meet fiber requirement
– Type of fat
» Feed saturated fats instead of unsaturated fatty
acids
» Feed inert fats
Whole seeds
Calcium salts of long chain fatty acids
Prilled fat
• Effects on mineral absorption
– If feeding unsaturated fats, the amounts of Ca and
Mg fed should be increased by 20 to 30%
• Effects on milk protein percentage
– Supplementing ruminally undegraded amino acids
– Supplementing nicotinic acid at 12 gm/d
– Considerations in choosing a supplemental fat
source
• Inertness
– CaLFA or > Whole oil seeds > Tallow > Vegetable oils
Prilled fat
• Other nutritional concerns
– Protein
» In no protein needed, supplement tallow
» If degradable protein needed, supplement raw
seeds
» In undegradable protein needed, supplement
with undegradable protein source
Heat-treated soybeans
DDGS
– Fiber
» If fiber is needed, supplement whole cottonseed
– Antiquality factors
» Gossypol in whole cottonseed
Limit whole cottonseeds to 8 lb/day
• Price per pound of fat
– Protected fats ($1.50/lb fat)
– Oil seeds (.82-1.12/lb fat)
– Tallow ($.25/lb fat)
– Vegetable oil ($.49/lb fat)
• Timing of supplementation for dairy cows
– Delay supplementation of fat until weeks 6-7 of
lactation
» If can’t delay because of feeding TMR, limit
maximum supplementation to 2.5% of DM
– Fat supplementation should be terminated to prevent
the cow’s body condition to not go above 3.5 on a 5point scale