html5-img
1 / 76

Lipid Metabolism In Ruminants

Lipid Metabolism In Ruminants. G. R. Ghorbani. Overview. Herbivores diets are normally quiet low in lipid because of the small quantity (2-5%) contained in most plant food sources.

arden-burke
Download Presentation

Lipid Metabolism In Ruminants

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lipid Metabolism In Ruminants G. R. Ghorbani

  2. Overview • Herbivores diets are normally quiet low in lipid because of the small quantity (2-5%) contained in most plant food sources. • These dietary characteristics have required both metabolic adaptations and methods for conserving essential fatty acids (EFA). • Plant lipids are altered extensively by the rumen fermentation, and the lipid actually received and absorbed by the animal differs from that ingested.

  3. Overview • The rumen is intolerant to high levels of fat, which may upset the fermentation. • This situation in functioning ruminant contrast with that in the newborn ruminant, which ingests milk at about 30% or more fat in the DM, representing 50% or more of its caloric intake.

  4. Overview • In most metabolic systems FA’s are derived from glucose. • Dietarily derived glucose is scarce in ruminant metabolism, however and ruminants have evolved mechanisms for its conservation, the most important of which is the lack of pathways for converting glucose into FA’s.

  5. Overview • About 90% of fat synthesis in ruminants occurs in the adipose tissue. • The liver, which is the major lipogenesis site in many non-ruminants species, accounts for only 5% in ruminants.

  6. Plant Lipids • Lipids can be grouped into storage compounds in seeds (TG), leaf lipids (galactolipids and phospholipids), and a miscellaneous assortment of waxes, carotenoids, chlorophyll, essential oils and other ether-soluble substances. • TG are negligible in forages. • Leaf lipids are mainly galactolipids involving glycerol, galactose, and unsaturated FA’s.

  7. Plant Lipids • The leaf lipids are generally more polar than TG’s and have a lower energy value than would be estimated by the 2.25 factor used to calculate TDN. • The FA’s associated with GL and many of the TG’s of the seed organs are relatively unsaturated and contain high amounts of linoleic and linolenic acids (Table 1).

  8. Table-1. content and composition of EE from forage leaves

  9. Triacylglycerol Triglycerides R-COO-CH2 R-COO-CH R-COO-CH2 • Triglycerides found in seeds and • animal adipose. • Diglycerides found in plant leaves, • one fatty acid is replaced by a sugar • (galactose).

  10. Triglyceride Containing Linoleic Acid Omega-6

  11. Linolenic Acid Omega-3

  12. Fatty Acid Isomers

  13. Lipolysis • Shortly after esterified plant lipids are consumed, they are hydrolyzed extensively by microbial lipases, causing the release of constituent FA’s. • Anaerovibrio lipolytica , which is best known for its lipase activity, produces a cell bound esterase and a lipase. • The lipase is an extracellular enzyme packaged in membranous particles composed of protein, lipid, and nucleic acid.

  14. Lipolysis + 3H20 + Lipases Esterified Plant Lipid Free Fatty Acids

  15. Lipid DigestionRumen -galactosidase DigalDigly MonogalDigly Galactose Propionate Diglyceride Glycerol Triglyeride Fatty acids Saturated FA CaFA Ca++ Feed particles -galactosidase Lipase Anaerovibrio lipolytica H+ Reductases Lipase

  16. Lipolysis • The lipase hydrolyzes acylglycerols completely to FFA, glycerol and galactose with little accumulation of mono or diglycerides. • Glycerol and galactose are fermented rapidly, yielding propionic and butyrate acid as a major end product. • Despite its high lipase activity, the general esterase activity in A.lipolytica is lower than in many non lipolytic bacteria.

  17. Hydrolysis of lipids in the rumen (Bath & Hill 1969) % of Total Lipid Total Lipid % TG DG MG PL FFA Diet* 6.3 72.4 13.7 1.7 1.2 11 Rumen digesta, 0 h 5.1 .1 .0 .1 15.2 85 Rumen digesta, 1 h 6.2 30.4 1.7 .0 7.1 61 Rumen digesta, 5 h 6.4 11.1 .0 .0 12.4 76 *Diet consisted of 1 kg chopped hay + 50 g of palm oil

  18. Lipolysis • Fay et al identified 74 strains of ruminal bacteria that were capable of hydrolyzing the ester bond. • Known lipolytic strains, including A lipolytic, and Butyrivibrio fibrosolvens, had low hydrolysis in that assay. • Also, bacteria with general esterase activity are not necessarily capable of hydrolyzing lipid esters. • Hespell and O’Bryan-shah found a wide variety of ruminal bacteria with esterase activity, including 30 strains of B. fibrosolvens, but only a few bacteria could hydrolyze long chain fatty acids (LCFA)

  19. Lipolysis • The extent of hydrolysis is very high for most unprotected lipids: 85-95%. • This % is higher for diets rich in fats than for conventional diets, in which most lipids are in cellular structures. • Hydrolysis seems to be highest for diets rich in protein.

  20. Lipolysis • Gerson et al. have shown that lipase was more active with diets rich in fiber than for diets rich in starch, but that a short-term supply of starch in a fiber diet could increase lipolysis. • This suggests either that the rate of lipolysis could depend on the microbial ecosystem, or that variations of ruminal pH control lipase activity.

  21. Lipolysis • Protozoa are not involved to any great extent in hydrolysis, except for that of phospholipids. • Salivary lipase present in ruminants has a very low activity, whereas in monogastric animals it plays a more important role

  22. Biohydrogenation • Unsaturated FFA have relatively short half lives in ruminal contents because they are rapidly hydrogenated by microbes to more saturated end products. • The initial step in biohydrogenation (BH) is an isomerization reaction that converts the cis-12 double bond in unsaturated FA’s to a trans-11 isomer.

  23. Biohydrogenation • Reduction of double bonds • Result: fatty acids that are more saturated with hydrogen Unsaturated Saturated

  24. Linolenic Acid Omega-3

  25. Hydrogenation of Fatty Acids in the Rumen Polyunsaturated fatty acids (all cis) Isomerase (from bacteria) Needs free carboxyl group and diene double bond Shift of one double bond (cis & trans) Hydrogenation Hydrases (from bacteria, Hydrogenated fatty acid mostly cellulolytic) (stearic and palmitate)

  26. Hydrogenation of Fatty Acids in the Rumen • All unsaturated fatty acids can be hydrogenated • Monounsaturated less than polyunsaturated • 65 to 96% hydrogenation • Numerous isomers are produced • Biohydrogenation is greater when high forage diets fed • Linoleic acid depresses hydrogenation of FA

  27. Biohydrogenation • The isomerase is not functional unless the FA has a free carboxyl group, and in the case of PUFA;s such as C18:2, a cis-9, cis-12 diene double bond configuration is present. • The requirement of a free carboxyl group establishes lipolysis as a prerequisite for biohydrogenation .

  28. Biohydrogenation • Once the trans-11 bond is formed by action of the isomerase, then hydrogenation of the cis-9 bond in C18:2 occurs by a microbial reductase. • The extent to which trans-11 C18:! Is hydrogenated to C18:0 depends on conditions in the rumen. • For example, complete hydrogenation to stearic acid is promoted by the presence of cell-free ruminal fluid and feed particles, but it is inhibited irreversible by large amounts of linoleic acid.

  29. Biohydrogenation • Linolenic acid is often completely hydrogenated in stearic acid. • The hydrogenation of linleic acid is not complete.. • It provides stearic acid and different monounsaturated isomers, of which trans-vaccenic acid is characteristic of ruminal metabolism

  30. Biohydrogenation 18:2 converted (%) Time (h) • (adapted from Harfoot et al., 1973)

  31. Conjugated Linoleic Acid - RumenMost Common Pathway (High Roughage) Linoleic acid (cis-9, cis-12-18:2) Conjugated linoleic acid (CLA, cis-9, trans-11- 18:2) Vaccenic acid (Trans-11-18:1) Stearic acid (18:0) Cis-9, trans-12 isomerase Butyrivibrio fibrosolvens At low rumen pH, trans-10, cis-12 isomer of CLA is produced.

  32. CLA absorbed from the intestines available for incorporation into tissue tryglycerides. Reactions from linoleic acid to vaccinic acid occur at a faster rate than from vaccinic acid to stearic acid. Therefore, vaccinic acid accumulates in the rumen and passes into intestines where it is absorbed. Quantities of vaccinic acid leaving the rumen several fold greater than CLA.

  33. Conversion of Vaccinic Acid to CLA • In mammary gland and adipose • Trans-11-18:1 CLA, cis-9, trans-11 18:2 • Stearoyl CoA Desaturase • ‘9-desaturase’ • This reaction probably major source of CLA in • milk and tissues from ruminants. • Also transforms • Palmitic Palmitoleic • Stearic Oleic

  34. CLA Isomers - Rumen (High Concentrate)Low Rumen pH Linoleic acid (cis-9, cis-12-18:2) Cis-9, trans-10 isomerase CLA Isomer (trans-10, Cis-12-18:2) This isomer is inhibitory to milk fat synthesis. Trans-10-18:1

  35. Effect of CLA isomers on milk fat % Infusion 3.5 3 c/t 10,12 CLA Milk Fat, percentage 2.5 c/t 9,11 CLA Control 2 1.5 -2 -1 1 2 3 4 5 6 7 8 Day Baumgard et al. (2000)

  36. Potential Value of CLA in Foods of Ruminant Origin • Anticarcinogenic effects in lab • animals given chemicals to cause cancer • Reduce atherosclerosis • Direct evidence with rabbits • Indirect evidence with humans • Reduce fat accumulation in the body • Laboratory animals and pigs • Evidence not conclusive with humans

More Related