Synthesis of fat

a) Precursors of Long chain fatty acids:

• The fatty Acids in the cow’s ration provide directly about one half of the fatty acids.
• The unsaturated long chain fatty acids in diet of the cows from plant origin get hydrogenated (saturated) in the rumen.
• This process is not hundred % efficient in saturating all of the fatty acids in the feed.

b) Precursors of Short chain fatty acids:

• Short chain fatty acids that comprise the 50% of milk fat not derived directly from the fatty acids of the ration are synthesized in the mammary secretary cell from acetate and a ketone body β hydroxybutyrate.
• Acetate is two carbon unit where as BHBA is a four carbon molecule, and both molecules are derived from the fermentation of carbohydrates in the rumen to volatile fatty acids.
• In this reaction the chain two carbon atoms increase length at a time because acetate molecules are added stepwise.
• In the case of BHBA, the 4-carbon molecule is cleaved to 2 carbon units and utilized similar to acetate.
• More acetate than β-hydroxybutryrate is used for milk fat synthesis.
• Acetate can enter a glycolytic pathway to provide energy for the mammary cell.