Milk fat origin

Since about 50% of C16 0 and 100% of C18 0, C18 , and C18.2 are derived from blood lipids, about 50% of the total fatty acids in ruminant milk fat originate from the blood via diet or other organs. 

Milk Fat Origin of Fatty Acids and Influence of Nutritional Factors Thereon... 

About half the total acids of milk fat arise from blood lipids and the rest from de novo synthesis in the mammary gland. Ultimately all the acids of milk fat originate from the products of digestion, but not all do so directly some come from endogenous acetate and fatty acids after storage and mobilisation in the body, particularly in early lactation. 

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