Milk fat matters: How to maximize milk fat yield on farm

By Grace Praisler, Vita Plus dairy specialist

Milk fat contributes a significant amount to the monthly milk check. As a result, it is important for dairy farmers to maximize milk fat yield to improve herd profitability. Various nutrition and management factors can impact milk fat yield in dairy cows, including feeding supplemental fat sources, providing the precursors for de novo fatty acid synthesis, and mitigating the risks for decreased milk fat synthesis.

To better understand milk fat, let’s break it down into three fatty acid categories:

1. De novo fatty acids (short-chain; C4 to C12) are created by the mammary gland from volatile fatty acids (acetate and butyrate), which are produced in the rumen via microbial fermentation of feed.
2. Preformed fatty acids (long-chain; C18 or greater) originate from absorbed dietary fat sources or mobilized body reserves.
3. Mixed fatty acids (medium-chain; C14 to C16) are a blend of de novo and preformed fatty acids and can be influenced by fat supplementation.

Milk fat depression

Milk fat depression is the drastic decrease in milk fat yield due to the production of incomplete biohydrogenation intermediates in a disrupted rumen environment. These intermediates are absorbed by the cow and will directly inhibit de novo fatty acid synthesis in the mammary gland.

Risk factors that can directly disrupt the rumen environment include feeding large amounts of rumen accessible unsaturated fatty acids (i.e., conventional soybeans, distillers grains) or rapidly fermentable starch sources (such as high moisture corn), low rumen pH, sorting, heat stress, and decreased cow lying time.

Considerations to mitigate the risk of milk fat depression to maximize milk fat yield include:

• Quality forages: Feed quality and physically effective forages that support fiber digestion and a consistent rumen environment and reduce sorting behavior.
• Nutrition: Monitor the amounts of unsaturated fatty acids and rapidly fermentable starch sources in the ration. Provide adequate amounts of digestible fiber and sugar. Employ amino acid balancing and consider additives that can improve rumen pH, such as buffers and yeasts.
• Feed availability and management: Consistent feed availability decreases slug feeding behavior. Follow feeding protocols, such as proper mixing, to ensure a consistent feed is dropped from the beginning to the end of the feedbunk. Maintain a regular pushup schedule to ensure quality feed is always accessible to help maintain a healthy rumen.
• Cow comfort: Optimize cow comfort by avoiding overcrowding. This can be done with properly sized stalls in a well-ventilated barn with fans and sprinklers to reduce heat stress and bunching. Other considerations include implementing fly control methods and providing clean, dry bedding to increase cow lying time.

Provide precursors

The products of the ruminal fermentation of fiber (acetate) and sugar (butyrate) are used by the mammary gland to produce de novo fatty acids.  Rations with adequate amounts of digestible fiber and sugar ensure acetate and butyrate are available.  Digestible fiber sources include quality forages, soyhulls and corn gluten feed.  Sugar sources include candy byproducts, whey permeate and molasses-based liquid feeds.  Whey permeate also provides significant moisture to the ration, reducing sorting behavior.  Additionally, formulating rations with adequate amino acid content can also improve de novo milk by providing amino acids for the biological pathways of milk fat synthesis.

Supplementing fats

Supplementing greater amounts of fat provides the cow the opportunity to incorporate additional dietary preformed fat into milk fat. Fat sources that have been reported to aid in increasing milk fat yield include whole cottonseed, high oleic soybeans and rumen-inert fat sources. These fat sources are more rumen-friendly due to their fatty acid profiles and/or limited accessibility to rumen microbes. They can be absorbed by the cow without disrupting the rumen and used for milk fat synthesis in the mammary gland.

The best way to maximize milk fat yield on your dairy is to supplement the right dietary fat sources to increase preformed fatty acids and not limit de novo fatty acid synthesis through good nutrition and management. Reach out to your Vita Plus consultant to discuss how to improve milk fat yield and your herd’s profitability.