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Optimising milk fat strengthens dairy profits

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Fat found in milk originates from three sources; de novo fatty acids synthesised in the milk gland of the cow (short-chain C4 to C14) comprise about 20-30% of total milk fatty acids, preformed fatty acids (long chain C18:0, C18:1 and C18:3) represent 35-40%, and the mixed group of fatty acids (C16) make up about 35%.

Research has shown that the percentage of milk de novo fatty acids is positively correlated with the percentage of fat and true protein in the milk. It has also been indicated that these short-chain fatty acids explain nearly 50% of the variation in milk fat percentage and as much as 68% of the variation in milk true protein. De novo fatty acids are crucial and can be used to monitor herd management.


Key drivers of dairy profitability

Indeed, milk fat and protein are two key drivers of dairy profitability positively related to net milk income over feed costs. The quantity of de novo fatty acids reflects rumen functioning, especially fiber fermentation which produces acetate and butyrate, the building blocks of fatty acids. The relative proportion of de novo fatty acids in milk fat reflects how well the cow is being fed and managed for optimal rumen fermentation. Higher de novo fatty acids in the milk reflect healthier rumen conditions.

The intrinsic digestibility of the forage fiber is a function of plant genetics, maturity at harvest and growing environment, which determine the amount of lignin. Rumen pH has a large impact on the fiber fermentation. Thus, poor feeding management can influence rumen pH and subsequent fiber digestion and microbial protein production. Furthermore, recent research has shown that feeding or management practices reducing pH results in accumulation of CLA isomer that has a powerful milk fat depressing effect. So, the question is what management practices enhance rumen conditions as reflected by the de novo fatty acid content of the milk?


Fatty acids profiles evaluated

A study run in 2014 and 2015 utilized data collected from over 70 farms in northern New-York and Vermont assessing management and feeding practices, and this information was compared with bulk-tank milk composition. By evaluating fatty acid profiles, herds were categorized as either high or low de novo herds. The major factors consistently associated with greater de novo milk fatty acid content and higher milk fat and true protein content are presented in the infographic below.

In conclusion, butterfat levels in milk are affected by various factors. The sources of these fatty acids include de novo (synthesized), performed, and mixed fatty acids. Factors affecting de novo fatty acids have proven significant and account for much of the milk fat variability, the greatest of which appears to be rumen pH. Attention to the management and nutritional factors previously listed can help support pH and milk fat levels.


Major factors associated with greater de novo milk fatty acid content.

Stocking rates

  • Do not overstock pens or feeding area
  • The relationship between stocking density and de novo fatty acid content in milk makes sense given that overstocking increases are feeding rate and aggression at the feed bunk, depresses rumination, and increases the risk for lower rumen pH.

Feeding frequency

  • Feed more frequently (minimum twice a day)
  • Greater frequency of feeding enhances milk components and the de novo fatty acids which reflect rumen pH.

Ration balance

  • Feed fat properly and meet fiber requirements
  • Feeding too much-unsaturated fat may depress rumen fiber fermentation, and feeding too much rumen by-pass fat may simply drive up the preformed fatty acid content even when rumen conditions are not optimized for higher de novo fatty acid content in milk.

Levels of NDF

  • Utilise proper levels of physically effective Neutral Detergent Fibre (peNDF)
  • Dietary peNDF is important for enhancing de novo synthesis. That makes sense given the long-known relationship between effective dietary fiber, rumen pH, and microbial fiber fermentation.


  • Use additives/components to support rumen fermentation
  • Feeding additives which have been shown to support rumen pH and improve fiber digestion can improve de novo milk fatty acids. Yeast products such as RumenYeast® or Hilyses® have been shown to offset the typical pH reductions common with feeding higher levels of starch. RumenYeast® has also been shown to improve digestibility’s in the rumen supporting increased butterfat and resulting in a production improvement of +2kg/head/day.
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