August 16, 2022


By Lee Kloeckner

Many dairy producers in Southeast Minnesota and Western Wisconsin are paid on the pounds of components they produce rather than the pounds of raw milk.  A new test to analyze milk fat composition is now available to dairy producers and consultants.  By knowing the composition of the milk fat, more informed decisions can be made to help improve rumen health, fat production, and profitability.  Along with increased fat production, researchers at Cornell University and Miner Institute have identified a positive relationship between groups of fatty acids and bulk talk milk protein content.  To better understand how the test can help improve component production, we must first understand the origin of the milk fat molecule.

The milk fat molecule is a triglyceride composed of a glycerol backbone and three fatty acids.  There are two sources of fatty acids and they are identified by the number of carbons.  The first source is the de novo fatty acids, and range from four to sixteen carbons in length.  These fatty acids are synthesized in the mammary gland from the volatile fatty acids, acetate and butyrate, which are produced in the rumen.  The second source is the preformed fatty acids, and range from sixteen to eighteen carbons in length.  As the name implies, they are not synthesized in the cow and come from either fat consumed in the diet or mobilized body fat.  Because sixteen carbon fatty acids come from either de novo synthesis or a preformed source, they are commonly identified as mixed fatty acids.

As previously mentioned, milk fat is composed of a glycerol backbone and three fatty acids.  The glycerol backbone makes up about 5.5% of the milk fat test while the fatty acids make up the remaining 94.5%.  In a normal bulk tank test de novo fatty acids make up 18 to 30%, preformed fatty acids make up 30 to 45%, and mixed fatty acids make up 35 to 40% of the total fatty acids.  It is the distribution of these fatty acids that is an indicator of rumen health and animal performance.

At the 2017 4-State Dairy Nutrition & Management Conference, Dr. Barbano, Cornell University, presented some relationships between fatty acid concertation (expressed as g/100 g milk) and bulk tank fat and protein tests on 40 dairy farms in the Northeast United States.  He also provided recommendations for a 3.75% fat test.  A healthy rumen produced more volatile fatty acids and results in a higher fat test.  The data presented by Dr. Barbano shows that the de novo fatty acids (r2 = 0.80) and mixed fatty acids (r2 = 0.88) had the highest relationship with the bulk tank fat test and recommended that de novo fatty acids be higher than 0.85 g/100 g milk and mixed fatty acids be higher than 1.40 g/100 g milk to achieve a 3.75% fat test.  A healthier rumen also produces more microbial protein, so along with a higher fat test, they also identified a relationship between de novo concentration and bulk tank protein test (r2 = 0.53) and recommended that to achieve a 3.10% protein test, the concentration of de novo fatty acids should be above 0.85 g/100 g milk.  The relationship between preformed fatty acids and bulk tank fat test is much lower (r2 = 0.07) and they did not report a recommendation.

There are several factors that can contribute to variability in the milk fat test with the largest factor being rumen health.  Rumen health can be impacted by several dietary and non-dietary factors.  Dietary factors may include the level of fiber, starch, and fats in the diet.  Consumption of spoiled feed may also impact rumen health.  There are also several other management factors that impact rumen health such as over-crowding, slug feeding, and cud chewing.  Factors that contribute to the amount of preformed fatty acids in the diet include fat supplied in the diet such as palmitic acid (16 carbons) and stearic acid (18 carbons).  Days in milk also has an impact on preformed fatty acids.  Early lactation cows are mobilizing adipose tissue to help meet their energy requirements and thus have a higher percentage of preformed fatty acids.

We know that the milk fat test can be broken down into the specific fatty acids, where these fatty acids originate, and how the compositions of fatty acids can impact the milk fat and protein tests.  Increasing the proportion of the de novo fatty acids is related to a higher fat and protein tests which results in more income for the farm.