LIPID DIGESTION

1
LIPID DIGESTION

• References
• Church 298-312

2

• 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 Form
• Corn and 4-20 Triglycerides
• other seeds
• Forages 4-6 Galactosyl
• 
  glyceryl esters
• pigments
• waxes, essential
• 
  oils

3

• Structure
• Triglyceride O
• 
  
• O C-O- C-R
• R-C-O-C O
• 
  
• C-O-C-R
  
• 46 oleic acid (181) and 42 linoleic acid
  (182)
• Galactosyl diglyceride
• 
  
  
  
• O C-O-gal O
  gal
• 
  
• R-C-O-C O
• 
  
• C-O-C-R
• 31-61 linolenic acid (183)

4

• Common fatty acids in ruminant diets
• Fatty acid CarbonDouble Bonds
  Double bond position
• Myristic 140
• Palmitic 160
• Palmitoleic 161 Cis-9
• Stearic 180
• Oleic 181 Cis-9
• Linoleic 182 Cis-9, 12
• Linolenic 183 Cis-9,
  12, 15
• Arachidonic 204 Cis-5, 8, 11, 14
• Eicosapentaenoic 205 Cis-5, 8, 11,
  14, 17
• Docosahexaenoic 226 Cis-5, 7, 10,
  13, 16, 19

5

• Unsaturated fatty acid isomers
• Cis isomers (Naturally found in feeds)
• H H
• \ /
• CC
• / \
• C C
• / \
• R R
• Trans (Found in ruminant meat and milk as well as
  hydrogenated oils)
• R
• \
• C H
• \ /
• CC
• / \
• H C
• \
• R

6

• Lipid digestion in the rumen
• 
  alpha-galactosidase
  beta-galactosidase
• O CH2-O-Gal-Gal
  O CH2-O-Gal
  O CH2OH
• 
  
  
  
• R1-C-O-CH2 O --------------------?
  R1-C-O-CH2 O ---------------------?
  R1-C-O-CH2 O
• 
  
  
  
• CH2-O-C-R2
  CH2-O-C-R2
  CH2-O-C-R2
• Galactosyl diglyceride
  
  
• 
  
  
• 
  
  
  Lipases
• 
  Galactose
  
• 
  
  
• 
  
  
• 
  Propionate
  ?------------Glycerol?--------
• 
  
  
• 
  
  
  Unesterified
• 
  
  FA
• 
  
  (Rn)

7

• 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
• Major alterations of long chain fatty acids in
  the rumen
• Biohydrogenation
• Microbial synthesis of long-chain fatty acids

8

• 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 182 CLA
• Obtained by ingesting bacteria
• Fungi have capability for biohydrogenation, but
  make up a small proportion of the microbial
  biomass

9

• Processes
• From Linoleic acid
• High roughage diet
• Linoleic acid (cis-9, cis-12 182)
• cis-9, trans-12
  isomerase
• from Butyrvibrio
  fibrisolvens
• (Rapid)
• Conjugated linoleic acid (CLA, cis-9,
  trans-11 182)
• Also called Rumenic
  acid
• cis-9 reductase
• from Butyrvibrio
  fibrisolvens
• (Rapid)
• Vaccenic acid (trans-11 181)
• trans-11 reductase
• from Clostridium
  proteoclasticum
• (Slow)
• Stearic acid (180)

10

• High grain diet (Low pH)
• Linoleic acid (cis-9, cis-12 182)
• trans-9, cis-12
  isomerase from
• Megasphaera elsdenii,
  Streptococcus bovis
• (Rapid)
• Conjugated Linoleic Acid isomer (trans-10,
  cis-12 182)
• cis-12 reductase from
• Megasphaera elsdenii,
  Streptococcus bovis
• (Rapid)
• Trans-10 181
• trans-10 reductase
• (Slow)
• Stearic acid (180)

11

• From Linolenic acid
• High roughage diet
• Linolenic acid (cis-9, cis-12, cis-15 183)
• Cis-9, trans-11, cis-15 183
• Trans-11, cis-15 182
• Vaccenic acid (trans-11 181)
• Stearic acid (180)

12

• Why do bacteria reduce unsaturated fatty acids
• Mechanism to use excess hydrogen
• Detoxify unsaturated fatty acids

13
Results of biohydrogenation in the rumen

• On all diets
• Higher concentration of saturated fatty acids
  leave than the rumen than enter in the diet
• Higher concentration of stearic acid (180) leave
  the rumen than enter in the diet
• High roughage diets
• High concentrations of CLA (cis-9, trans-11 182)
  and vaccenic acid (trans-11) 181 in the rumen
• High concentrate diets
• High concentrations of trans-10, cis-12 182 and
  trans-10 181 fatty acids in the rumen
• These fatty acids will be absorbed in the small
  intestine and represent a high proportion of the
  fatty acids presented to tissues

14

• Results of long-chain fatty acid metabolism
• 
  Feed
• Fatty acid Corn SBM Barley-SBM-Tallow Grass
• Saturated
• 140 - - 2.5 4.6
• 160 7.0 11.0 32.7 20.8
• 180 2.4 4.1 20.6
  3.3
• Unsaturated
• 161 - - .8
  2.4
• 181 45.6 22.0
  25.1 5.7
• 182 45.0 54.0 16.5 14.0
• 183 - 7.5 1.9 49.2
• 
  Intramuscular fat
• Swine
  Beef
• Saturated Barley-SBM-Tallow Grass
• 140 2.0 2.3
  2.7
• 160 23.8 27.4 22.8
• 18.0 10.6 16.0 14.7
• Unsaturated

15

• Tissue metabolism of trans isomers of fatty acids
• Conversion of trans-11 181 to CLA (cis-9,
  trans-11 182)
• Occurs in mammary gland and adipose
• Major source of CLA (cis-9, trans-11 182) in
  meat and milk
• Mechanism
• 9 - desaturase
• Trans-11 181
  CLA (cis-9, trans-11 182)
• 
  2H

16

• 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
  182) in ruminant meat and milk
• Anticarcinogenic
• Reduces atherosclerosis
• Alter body composition
• Diabetes control
• Improved immune response
• Improved bone mineralization
• Milk fat depression in lactating dairy cows
• trans-10 , cis-12 CLA 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

17

• 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
• C180 and C160
• 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

18

• 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

19

• Mechanism of lipid digestion in small intestine
• Unesterfied Triglyceride
  Phospholipid
• fatty acids
• Pancreatic
  Phospholipase A1
  lipase
  Phospholipase A2
• Unesterfied Monoglyceride
  Lysolecithin
• fatty acid
• Bile salt
• 
  Phosphatidylcholine
• 
  Phosphatidylethanolamine
• Micelles
• Absorbed into
  mucosa
• Micelles break
  up
• Fatty acids lt 14 C are transported directly
  in the blood
• 10 of the 180 is
  desaturated to 181
• Long chain fatty acids combine with
  lipoproteins to produce VLDL and
  chylomicrons

20

• 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
• Freeesterified cholestrol ratio is 41 compared
  to 11 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

21

• 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

22

• Fat depots
• Location
• Subcutaneous
• Inter and intramuscular sites
• Visceral sites
• Fatty acid composition
• General
• 80 of FA are 140, 160, 180, and 181
• Small amounts of 182 and very little 183
• 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

23
Roles of lipid stores in the body of ruminant
animals

• Provides an energy reserve when needed
• Provides internal insulation against cold stress
• Maintenance of reproduction
• Long-term feed intake control

24
Proportion of empty body lipid at each condition
score and the amount of energy provided by losing
1 body condition score unit (9-point scale)
25
Effects of excessive mobilization of fat stores

• Metabolic diseases
• Ketosis in dairy cattle
• Pregnancy disease in sheep
• Causes
• Animal factors
• Dairy cows
• High production
• Reduced feed intake immediately before and after
  calving
• Ewes
• Multiple fetuses
• Metabolic factors
• Excessive mobilization of fat reserves
• Inadequate blood glucose

26

• Ketosis-fatty liver syndrome (Dairy cattle)
• In early lactation, energy must be
  mobilized from tissue reserves
• 
  Inadequate
  glucose
• Excessive mobilization of adipose tissue
  
• 
  
  Lack of OAA
• 
  
  Lack of carnitine
• 
  
  Lack of niacin
• Overcomes limit of fatty acids to be
• transported from liver as VLDL
• oxidized in TCA cycle in liver
• Fat accumulates Acetyl-CoA
  
• in hepatocytes
• (Fatty liver)
  Acetoacetate
• 
  B-OH-Butyrate Impairs gluconeogenisis
• Impairs feed intake
  Appear in milk Reduces
• 
  
  glucose

27
From Van Soest, 1994
28

• Symptoms
• Metabolic profile
• Normal
  Ketosis (2-4 weeks PP)
• Blood
  mg
• Glucose 52
  28
• Ketones 3
  41
• Plasma
• Free fatty acids 3
  33
• Poor appetite
• Loss of body weight
• Gaunt and dull appearance
• Irregular rumen contractions
• May stagger or appear uncoordinated
• Milk production will decrease
• Complications
• Displaced abomasum, milk fever, retained
  placenta, and mastitis
• In ewes,
• Death

29

• Ketosis or pregnancy disease prevention
• Avoid excessive fatness (or thinness) in cows or
  ewes
• Maximize intake immediately before calving (or
  during pregnancy in ewes)
• Avoid abrupt change to high grain lactation diet
  at calving
• Feed balance ration
• Use high quality forages
• Drench cows with propylene glycol (1L/day) for 1
  week daily before calving
• Propylene glycol is metabolized to lactate that
  can be used for gluconeogenisis
• Supplement with nicotinic acid (6 12 g/d) ?????
• Increases DMI
• Reduces lipolysis
• Recommendations
• Use in ketosis prone cows
• Use from 14 days prepartum to 120 days postpartum
• Use palatable carrier

30
ROLE OF LIPID STORES ON FEED INTAKE

• Leptin
• Produced primarily by white adipose tissue
• Also duodenum and mammary gland
• Concentration increases with increasing fatness
  or plane of nutrition
• Binds to Neuropeptide Y in the dorsomedial,
  ventromedial and arcuate nuclei of the
  hypothalamus
• Reduces long-term food intake and maintains
  energy balance

31
RELATIONSHIP OF LEPTIN WITH ENERGY BALANCE, BODY
CONDITION, FEED INTAKE IN LACTATING DAIRY COWS
(Reist et al., 2003)
32
EFFECTS OF LEPTIN ON REPRODUCTION

• Cows with higher leptin concentrations has
• Earlier first estrus after parturition
• Stronger estruses
• Accelerated puberty
• Mechanism
• Stimulation of GnRH in the hypothalamus
• Greater Follicle Stimulating Hormone
• Greater Luteinizing Hormone