VPB 121: Veterinary Physiology - II (2+1)

FATE OF RUMEN LIPIDS 

• Dietary lipids occur as structural lipids in forages and storage lipids in oilseeds.
• In forages, less than 50% of total lipids are free fatty acids and the majorityof them are phospholipids.
• In oilseeds, 65-80% of lipids are free fatty acids.
• Rumen microbes hydrolyse the dietary lipids to glycerol and free fatty acids.
• Glycerol is converted to propionic acid by the microbes.
• The metabolism of lipids by microorganisms  takes place in 4 steps:
  • Hydrolysis of esterified fatty acids.
  • Biohydrogenation of unsaturated fatty acids.
  • Lipid biosynthesis in the rumen.
  • Metabolism of phytal to phytanic acid.
• Hydrolysis of esterified fat
  • The rumen bacteria produce two hydrolytic enzymes, cell bound esterases and lipases. The triglycerides undergo rapid hydrolysis and give rise to high concentration of unesterified fatty acids especially when concentrates are supplemented in the diet.
• Biohydrogenation of unsaturated fatty acids
• The bacteria are capable of synthesising long-chain fatty acids and phopholipids from short chain fatty acids. 
  • The unsaturated fatty acids like linolenic acid present in grass is rapidly hydrogenated in the rumen yielding cis-trans dienoic acid, cis- trans monoenoic acids and stearic acid. This ability is present in bacteria as well as in protozoa. In a similar way linoleic acid is converted to conjugate dienoic acid, monoenoic acid and finally to stearic acid. The ability for biohydrogenation is greater with organisms like Butyrivibrio fibrisolvens and Ruminococcus albus. The hydrogen for biohydrogenation comes from the metabolic end products of carbohydrate fermentation.
•  Lipid biosynthesis of fatty acids
  • Acetate propionate and butyrate serve as the prime molecules for fatty acid synthesis and the malonate is used as extender of carbon chain in the fatty acid.
• Metabolism of phytal to phytanic acid
  • The chlorophyll of the leaf contain the isoprenoid alcohol known as phytal.. The phytal is hydrogenated to dihydrophytal which then get  oxidized to phytanic acid and incorporated in rumen organisms.

Synthesis of vitamins

• Vitamin K and many B complex vitamins (thiamine, riboflavin, nicotinic acid, pantothenic acid, cyanocobalamine, pyridoxine and biotin) are synthesised in rumen are absorbed from the rumen.
• When a diet is deficient in cobalt, synthesis of vitamin B12 will be inadequate.

Detoxification of toxic substances

• Toxic substances in plants (e.g.oxalates and gossypol) are detoxified in the rumen