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 feedsFeed % EE FormCorn and 4-20 Triglyceridesother seedsForages 4-6 Galactosyl glyceryl esters

+ pigmentswaxes,

essential oils

– Structure• Triglyceride O || O C-O- C-R || | R-C-O-C O | || 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 | || C-O-C-R

– 31-61% linolenic acid (18:3)

– Common fatty acids in ruminant diets Fatty acid Carbon:Double Bonds Double bond

position Myristic 14:0 Palmitic 16:0 Palmitoleic 16:1 Cis-9 Stearic 18:0 Oleic 18:1 Cis-9 Linoleic 18:2 Cis-9, 12 Linolenic 18:3 Cis-9, 12, 15 Arachidonic 20:4 Cis-5, 8, 11, 14 Eicosapentaenoic 20:5 Cis-5, 8, 11, 14, 17 Docosahexaenoic 20:6 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• • 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)• • • • O • ||

• O CH2-O-C-R1 • || | • R2-C-O-CH2 O • | || Lipases • CH2-O-C-R3 • Triglyceride

– 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 FeedFatty acid Corn Barley-SBM-Tallow conc GrassSaturated14:0 - 2.5 4.616:0 7.0 32.7 20.818:0 2.4 20.6 3.3Unsaturated16:1 - .8 2.418:1 45.6 25.1 5.718:2 45.0 16.5 14.018:3 - 1.9 49.2 Intramuscular fat

Swine Beef Saturated Barley-SBM-Tallow conc Grass14:0 2.0 2.3 2.716:0 23.8 27.4 22.818.0 10.6 16.0 14.7Unsaturated16:1 3.7 4.0 3.918:1 45.1 38.6 40.618:2 12.8 3.0 2.118:2 CLA - 0.4 1.118:3 0.8 0.7 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) Palmitoleic acid (16:1)» Stearic acid (18:0) 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

– 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 Triglyceride Phospholipidfatty acids

Pancreatic Phospholipase A1 lipase Phospholipase A2

Unesterfied Monoglyceride Lysolecithinfatty acid

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

– Breed differences

Delta-9 desaturase activity

Wagyu Holstein

Muscle 3.3 0.8

Adipose 132.1 39.5

CLA c9, t11

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0.20

0.40

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0.80

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1.20

1.40

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– 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 balanceReduce insulin and increase progesterone

Increases follicle size and numberReduce 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 seedsCalcium salts of long chain fatty acidsPrilled 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 sourceHeat-treated soybeansDDGS

– 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 5-point scale