The term "de novo fatty acids" has been popping up a lot recently thanks to emerging research on the fatty acid profile of milk, and specifically the level of de novo fatty acids within the profile. Some co-ops and Dairy Herd Improvement Association labs have started reporting these numbers on a routine basis; however, many dairy farmers are wondering what exactly de novo fatty acids are and why they should care about looking at them.

De novo fatty acids are an important part of the total butterfat number that most dairy farmers are familiar with. The total butterfat profile of milk is made up of many fatty acids. These fatty acids, which make up butterfat, can be lumped into three broad categories: de novo fatty acids, preformed fatty acids and mixed origin fatty acids. To explain what these three categories mean, we need to understand a little chemistry. One way we can tell the fatty acids apart is by the number of carbon atoms the fatty acid molecule contains. Typically the de novo fatty acids are estimated by adding up all the fatty acids that contain between four carbon atoms and 14 carbon atoms.

De novo fatty acids are made in the mammary gland of the cow and then excreted in milk. Preformed fatty acids are the sum of all fatty acids containing greater than 18 carbon atoms, and these fatty acids come from feed the cow eats or are mobilized from body fat of the cow, as they are not made in the mammary gland. Mixed fatty acids are the sum of the 16-carbon fatty acids. As the name implies, these fatty acids are a mix between fatty acids that the cow makes in the mammary gland and fatty acids that come from the feed.

Now, this can come across really technical, so it can be helpful to think about it like you think about your retirement portfolio. Analyzing your total butterfat number is like looking at the total value of your retirement account. The total number gives you a general idea of how well your account is doing, but doesn’t really give you enough detail to make strategic decisions that will help your overall number improve. To do that, you have to look at the individual performance of the investments within your portfolio to see which ones are growing and which ones might be costing you money. You can then make more strategic decisions on which funds you should continue to invest in and which ones might need to be removed to help improve the overall value of your account.

When we apply this thinking to our milkfat analysis and look beyond the total butterfat number, we can learn some important things based on the levels of the de novo, mixed and preformed categories. Since the de novo fatty acids are made in the mammary gland, they help give us a more precise understanding of how well the rumen is functioning. Looking at the de novo fatty acids in milkfat can be a good indicator of rumen fermentation since those fatty acids come from the acetic and butyric acids produced in the rumen. Identifying the amount of preformed fatty acids can give us a more precise understanding of how much body fat the cow is mobilizing and how well the ration is sustaining the animal. Mixed origin is a combination of these two sources.

Some of the recent research has provided the industry with guidelines for the ratios of each category. In early lactation, if cows are mobilizing body fat, you can expect to see an increase in the ratio of mixed and preformed fatty acids over de novo fatty acids. This is because the adipose tissue of the cow (cow fat) is high in C16 and C18 fatty acids (palmitic and stearic fatty acids, respectively). In mid-lactation cows, the ratio of preformed and mixed fatty acids to de novo fatty acids narrows because these cows are not mobilizing body fat. In this case, fatty acids that have less than 16 carbons would be higher. They will build up to form acetic acid from rumen fermentation and dilute out the preformed fatty acids.

By looking deeper into the butterfat number to see the amount that each of these three broad categories contributes, we can gain deeper insights and ultimately make better management decisions. To date, the de novo fatty acid category has been especially exciting because of the more precise information it gives us on the performance of the rumen. For a cow to efficiently convert feed and forage into the valuable components that a milk check is calculated on, then the rumen must be in prime condition, and the de novo fatty acid numbers help us gauge that.  

Mike Messman is a strategic technology lead at Cargill. Email Mike Messman.

SIDEBAR

Work at Cornell University has shown that a goal of milk fatty acids for Holstein herds should be:

• De novo: 0.8 grams per 100 grams
• Mixed origin: 1.3 grams per 100 grams
• Preformed: 1.3 grams per 100 grams