Milk fat – Composition and origin of fatty acids
Milk fat is present in milk as small, encapsulated droplets of triglycerides in an oil-in-water emulsion and is synthesised in the udder. With over 400 identified fatty acids, it is one of the most complex natural fats. Most of these fatty acids occur only in trace amounts, with only around 15 exceeding a proportion of 1%.
Fatty acid composition of milk fat
- Saturated fatty acids (without double bonds): approx. 65–70%
- Unsaturated fatty acids (C18:1, C18:2, C18:3): approx. 30–35%
Cows can synthesise fatty acids up to a length of 16 carbon atoms (C16:0) themselves. During de novo synthesis, the even-numbered fatty acids C4:0 to C14:0 are produced entirely, as well as approximately half of C16:0 (palmitic acid). These fatty acids are primarily formed in the udder from the precursors acetate (acetic acid) and beta-hydroxybutyrate (butyric acid), which are generated in the rumen during microbial digestion of feed (see diagram).
Propionic acid, formed in the rumen, serves as a precursor for glucose production and thus as the basis for the formation of milk sugar (lactose). A well-functioning rumen flora is therefore essential for high milk yield.
Milk fat – Origin of fatty acids
Fig. 1: Acetate is key in milk fat synthesis
Additional sources of fatty acids
The other half of C16:0 (palmitic acid) and the C18 fatty acids do not originate from the cow’s metabolism but come directly from the feed ration or from the mobilisation of body fat. Feed first enters the rumen, where 75–90% of the unsaturated fatty acids undergo biohydrogenation, converting them into C18:0 (stearic acid).
Approximately half of the milk fat originates more or less directly from the fatty acids in the feed ration, with stearic acid accounting for more than two-thirds of the fatty acid flow in the small intestine. Only a small portion of the unsaturated fatty acids – C18:1 (oleic acid), C18:2 (linoleic acid) and C18:3 (linolenic acid) – passes directly from the rumen to the udder and subsequently into the milk fat.
A large proportion of the C18:1 (oleic acid) present in milk fat does not come directly from the feed but is formed through the conversion of C18:0 (stearic acid) in the udder or adipose tissue (“desaturation”). This highlights the importance of an adequate supply of stearic acid in the cow’s diet.
Conclusion:
The fatty acid composition of milk fat results from a complex interaction between rumen bacteria, metabolic processes, and the composition of the feed ration. Targeted feeding with rumen-protected fats (BEWI-SPRAY® fat powders) can significantly influence milk fat quality. It is important to ensure an adequate supply of stearic acid while limiting the amount of palmitic acid.
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