As a dairy producer, you know low milkfat in your herd can take money out of your pocket. Additionally, it can be an extremely frustrating problem with no clear and simple solution. It’s important to know milkfat depression (MFD) is often a multifactorial issue requiring extensive problem solving and a holistic deep dive by everyone involved in the health, feeding and management of your herd. Irish poet Oscar Wilde put it best when he said: “The truth is rarely pure and never simple.”

Kvidera sara
Dairy Technical Consultant / Elanco Animal Health
Sara Kvidera was formerly a nutritionist with Micronutrients USA LLC.

So, what can you do if your milkfat levels are depressed? Here are four steps to help you think through milkfat concerns on your dairy farm.

1. Identify the issues 

The first step to solving any problem is to get a good handle on the problem itself. Evaluating your herd’s history can give you clues to help pinpoint changes that may have contributed to the problem. Here are some questions that help you take a step back and look at the bigger picture:

  • What have your production trends been over the past year? Is this a problem that happens suddenly, or is it typically a more-gradual onset?
  • What have your components been year over year? Are seasonal (summer) changes in milkfat similar to last year, or is there something different about this year that is causing milkfat to drop more than normal?
  • Is the issue only in one group? If milkfat patterns seem normal in your high group but are lower than expected in your late-lactation group, the issue may be group specific.
  • What variability has occurred in your feeds lately? Is dry matter variable? Does your ration match your formulated diet? What new feedstuffs are you using? What additives have you pulled or put in since the issue started?

2. Do a herd walk-through 

Check to see if your management strategies are working by walking through your barns. Prior to heat stress, it’s important to check heat abatement strategies. Are your soakers hitting cows where they should? Are water lines broken or clogged? Is there clean water, enough space for cows, etc.? Are feed troughs appropriately filled, and is the feed appealing to your cows? Ensuring your cows are in an environment that is pleasant to them so that they eat more, stay healthy and keep their rumen properly functioning is critical to achieving a good milkfat percentage. Sometimes, simple inconveniences to our cows prevent optimal productivity, and these aren’t always obvious until we get in the barn with them.

3. Review risk factors 

MFD is a multifactorial problem. No single total mixed ration (TMR) characteristic or component accounts for more than 10% of the variation in herd-level milkfat percentage. So it’s important to investigate all of the potential reasons your herd’s milkfat levels are suboptimal. Remedying one problem that may be causing your cows’ low milkfat without uncovering other likely reasons won’t solve the overarching issue. You need to look at the problem holistically to recognize why fixing one issue may not give you the milkfat percentages you really want.


Studies out of Penn State have shown that seasonality influences milkfat. Cows have evolved to produce lower milkfat in the summer, and in contrast, higher milkfat in the winter months due to nutrient-level needs for their calves. Young animals need more nutrients in the cooler winter months when there is less grass and grain available to consume. While poor heat abatement is a stress that could certainly be impacting milkfat levels, there’s also potentially a circadian rhythm aspect involved.

Outside of seasonality, extensive work has been done to better understand diet-induced MFD. Under certain conditions, the rumen can produce unique fatty acids, which are strong inhibitors of milkfat synthesis. Risk factors for creating these conditions can include:

  • Increased unsaturated fatty acids in the diet (consider dietary fat sources, amounts and availability)
  • Issues with the TMR such as mixing uniformity, consistent delivery and forage particle length
  • Cow comfort such as stocking density, time budgeting, heat abatement and access to fresh, clean water

4. Make a team plan

Diet-induced MFD is complex. Work as a team to decide what you can do to address the problem based on your barn walk-through and evaluation. Can feeding during cooler parts of the day help? Have you tried feeding more often? Is it worth paying a little bit more for a higher-quality feed? Should you consider feeding a yeast during the summer months to help control rumen pH? Producers and nutritionists should work in partnership to assess potential problems, implement strategies to address them and, over time, evaluate whether those strategies are correcting the problem.

A word about ionophores 

Some producers and nutritionists may think ionophores are a major contributor to lower milkfat percentages. However, before you lower levels or remove ionophores to preemptively avoid milkfat issues, it’s important to think about two things when weighing the risk versus the reward of ionophores: 

1. Pounds vs. percentage

Monensin works by helping increase production of propionate, a more efficient energy source and important precursor for glucose production in a cow. Glucose, in turn, contributes to lactose production, which is important in driving milk yield. In a 2008 meta-analysis of how monensin affects production, data showed milkfat percentage was reduced but milk yield was increased, resulting in no significant effect on milkfat yield. While milkfat percentage may be a fun statistic to brag about at the local coffee shop, pounds of solids shipped is what ultimately pays the bills in most situations. Furthermore, the meta-analysis showed it increased milk production efficiency (more marketable solids-corrected milk per pound of dry matter intake). This means monensin helps us derive as much energy as possible out of each pound of dry matter that a cow eats. In a market with high feed costs, it’s essential to get the most energy we can out of feed, and any additive that can help us reach our production goals is worth having in our toolbox. A more-efficient cow is good for the environment, good for productivity and good for dairy producers. 

2. Modern data in modern herds

Monensin was approved in 2004 before diet-induced MFD was fully understood. Over the past 20 years, the industry has made huge strides in how we feed dairy cattle to make a more productive and efficient animal. A combination of factors has made these “modern dairy diets” possible, including better cow genetics, higher-quality forage and a better understanding of diet-induced MFD. In 2018, a field study in 79 herds across the Northeast and Upper Midwest investigated associations between risk factors for MFD and milkfat percent in herds feeding monensin (Figure 1). They found no relationship between monensin and herd milkfat percentage, indicating that “monensin in diets does not directly cause milkfat depression, rather it most likely interacts with other dietary and herd-level factors when implicated in milkfat depression.”


Two studies recently conducted in 2020 identified how increasing levels of monensin affected milkfat and production efficiencies in diets formulated to maximize milk component production in dairy herds. In these two studies – conducted by a contract research organization in Fort Atkinson, Wisconsin, and by Cornell University in Ithaca, New York – monensin did not negatively impact milkfat, and it maximized production efficiency, as measured by energy-corrected milk divided by dry matter intake (DMI). Better feed efficiency with no negative impact on milkfat certainly leads to a better bottom line.

Look at the big picture

We often want to simplify complex interactions and issues by pinning a problem on one thing that needs adjusting. In reality, the interaction of nutrition, management and health is complex, and a holistic fix of the factors that need correcting will result in a stronger bottom line, an improved product, and a healthier and more productive herd. 

The label contains complete use information, including cautions and warnings. Always read, understand and follow the label and use directions. Caution: Consumption by unapproved species or feeding undiluted may be toxic or fatal. Do not feed to veal calves.

Feeding directions

Dairy cows: For increased milk production efficiency (production of marketable solids-corrected milk per unit of feed intake):

Total mixed rations (“complete feed”): Feed continuously to dry and lactating dairy cows a TMR containing 11 to 22 grams per ton monensin on a 100% dry matter basis.

Component feeding systems (including top dress): Feed continuously to dry and lactating cows a Type C medicated feed containing 11 to 400 grams per ton monensin. The Type C medicated feed must be fed in a minimum of 1 pound of feed per cow per day to provide 185 to 660 milligrams per head per day monensin to lactating cows or 115 to 410 milligrams per head per day monensin to dry cows. This provides cows with similar amounts of monensin they would receive by consuming TMRs containing 11 to 22 grams per ton monensin on a 100% dry matter basis.