Beyond Energy – What Signals are your Fatty Acids Sending?

It’s early June and the first heat wave of the summer is in full swing.  You have just finished vet check and hopped in your truck to head back to the office. Glancing at the temperature gauge on your dashboard, you see it’s 88 degrees already and only 9 in the morning.  Arriving back at your office, you decide to check the co-op’s dashboard to see how your components are trending.  Not surprising, you notice that milk fat has dipped down to 3.9% versus the 4.1% you were enjoying just a month ago. You text your nutritionist:  Milk fat is down.  Should we increase the palmitic in the diet?

Ok, let’s hit the pause button for just a second.  The question you just posed is a logical one:  Milk fat is down.  Palmitic increases milk fat.  Therefore, let’s feed more!  If only feeding fatty acids were that simple.  Newton’s third law states for every action in nature, there is an equal and opposite reaction.  Likewise, your simple request of feeding more palmitic is doing far more than simply increasing fatty acids diverted to the mammary gland to make milk fat percent (more on that later!).

Fatty Acids = More than Energy

If we look back at the history of feeding fat to dairy cattle, the main reason fat supplements were created was to increase the energy density of diets (beyond what the rumen can handle with corn) to support the needs of high producing cows more efficiently: milk and component production, body condition and maintenance, and certainly reproduction.  Today, we understand it’s far more complicated than simply staying in a target range on % total fatty acids and keeping a close eye on RUFAL (rumen unsaturated fatty acid load) to stay in the ‘safe zone’ regarding milk fat.  While some fatty acids are simply an energy source (mainly stearic), other fatty acids are signaling nutrients that are orchestrating a whole host of important functions in the cow.

Fatty Acids as Signaling Nutrients

Let’s walk through the main fatty acids found in dairy diets and talk specifically about the signals they are sending beyond being utilized for energy.  While they may seem complex, the stakes are high in understanding their roles as there is a rare function of the cow that is not impacted by fatty acids. 

Palmitic (16:0) and Oleic (18:1) are the two primary fatty acids in most fat supplements. While palmitic has stolen the limelight due to its ability to direct more fatty acids to the mammary gland, Oleic is just as critical due to its role in improving total energy available to the cow through greater fatty acid digestibility.

Feeding too much palmitic and not enough oleic results in fewer fatty acids available for the cow to maintain body condition, lower feed efficiency and can be detrimental to reproductive results, especially when fed in early lactation. The Palmitic:Oleic blend study by de Souza (2018) demonstrated the effects that too much palmitic versus oleic in the fresh pen can have on body condition: lower body condition persisted out through nine weeks even though cows from all treatments were fed a common diet after three weeks fresh (figure 1).

Excessive fatty acid levels can be a primary culprit for dragging down milk fat. Specifically, too much Linoleic (18:2) in the rumen can send unwanted signals to the mammary gland that directly reduce milk fat production. Linoleic, which is in corn, distiller’s grains, corn silage, cottonseed, and soybeans, is more than abundant given these sources are really the base of most diets. A recent meta-analysis by Diaz (2020) showed that increasing linoleic had a linear negative effect on milk fat %, at a rate of 0.18 percentage points per 100 grams of linoleic consumed. Certainly, the less protected those fatty acids are when they hit the rumen (aka distiller’s grains vs. a rumen-protected fat), the greater likelihood for milk fat to be negatively affected. On a separate note, linoleic is actively involved in immune regulation, since as an omega-6 it is a precursor to many pro-inflammatory molecules, including prostaglandins. 

Lastly, the omega-3 fatty acids are essential for immune regulation and reproduction. While linolenic (18:3) is the plant-based form of omega-3, it needs to be converted to EPA/DHA, the bioactive form of omega-3. Most of the linolenic in dairy diets are coming in through hay and grass silages, but because the same enzyme needed to convert ALA to EPA/DHA is used in the omega-6 pathway, the conversion rates are extremely low (~0.5%). 

EPA/DHA (20:5/22:6) are the essential omega-3s that are highly involved in signaling both for pregnancy (figure 2) and immune function. 

• Embryo Development & Retention: Recent research has shown a low-level inclusion of DHA in-vitro resulted in a doubling of the day-7 blastocyst growth rate (Oseikria 2016), and similar increases in the percent good quality embryos when EPA/DHA was fed (Freret 2019).  These findings underscore the essential role EPA/DHA plays in not only pregnancy retention (Santos 2005), but also in those very early stages of embryo development. 
• Resolving Inflammation: EPA/DHA omega-3 is the precursor to the immune molecules that are responsible for resolving inflammation.  Without adequate levels of EPA/DHA, inflammation will take longer to resolve, leading to more cows with chronic inflammation, lower fertility, and a greater likelihood of being a repeat visitor to the hospital pen.

Consequences of Imbalance

Now that we’ve reviewed the individual fatty acids and their basic signaling pathways in the cow, let’s get back to the practical challenge at hand: making decisions on how fatty acids are fed that support all of your goals on your dairy and not just milk fat percent. Let’s go back to how we started this discussion, looking at your downtrend on milk fat % and your idea to increase palmitic to ‘fix’ the issue.  What other questions should be asked before determining the best way to proceed? Here’s a few that come to mind:

• What is the current state of body condition in the herd, and specifically the fresh pen?
• Do you have the ability to target feed more palmitic to later lactation cows, rather than shifting to more palmitic/lower oleic early in lactation where you’ll likely have unintended consequences to body condition?
• What is your pattern of performance in the fall…how long do your cows take to recover from summer before they are back to posting the high conception rates you expect? A long rebound period can be a telltale sign of opportunity to better support the cow’s essential fatty acid needs. 
• What is your trend on pounds of components, not just milk fat percent? While the percent is important, it is not what you are getting paid on. Milk fat percent is worth nothing if it is not multiplied by pounds of flow to quantify to pounds of fat and protein that determine your milk check. 
• How much linoleic is in the diet and from what sources? Could shifting the total grams or the source for less rumen activity (ie. feed less distillers and more corn silage) help support your milk fat goals?

When we take a healthy pause…and consider not only the short-term goal of propping up milk fat percent in summer, but the longer-term goals of high fertility and health, your conclusion on how to proceed might be quite different. I’d argue that summer may be the worst time to feed higher levels of palmitic (and less oleic) to dairy cows, certainly during the first 1/3 of her lactation…encouraging more body condition loss during a high stress period, leading to lower fertility and slower rebound out of summer. 

Our human nature is to ‘measure everything.’ I certainly empathize with this need, and I was trained this way as well!  When it comes to fatty acids, however, this approach can often steer us wrong by keeping us hyper-focused on the short-term effect (milk fat %) and ignoring the longer-term effects of body condition, reproduction, and health. It is easy to do…especially the past few years where margins have been tight. But in this season of $700 beef cross calves and high replacement costs, it is critical that we are not prioritizing fatty acids for the mammary gland over fatty acids the cow herself needs for creating healthy embryos and maintaining body condition so that she can bounce out of summer. Balance wins in the end.