Milk fat depression (MFD) syndrome is a prevalent problem in many dairy herds feeding high-yielding dairy cows. A significant increase in understanding of MFD syndrome occurred in the last several years, and, clearly, different factors may be acting individually or together to result in a lower milk fat content. This article is focused on some of the possible dietary factors involved with MFD. One of the first steps nutritionists evaluate when they face a MFD problem is the dietary effective neutral detergent fiber (efNDF). Penn State University developed a method to evaluate the dietary efNDF which is based on the particle size of the forages or the total mixed ration. A minimum dietary efNDF guideline of 22 percent is required to provide a healthy rumen environment and maximize a cow’s intake, milk yield and composition.

Sometimes in a herd with a high prevalence of lame cows and MFD, the solution may just be adjusting the efNDF of the diet, but the solution is not always so simple.

Recent articles indicate some minerals in the diet can be associated with variations in milk fat. Studies from Ohio State University show the increased concentration of sulfur (over animal requirement) in the diet may affect dry matter intake (DMI), milk yield and milk composition, including fat and protein content. These effects were greater when increased concentrations of selenium were fed, indicating a negative interaction between these two minerals.

More recently, other researchers supplied different sources of inorganic forms of trace minerals (zinc, copper, manganese and cobalt) and complex trace minerals to dairy cows. They found effects on lactation performance variables (reproduction and health parameters), including milk yield and fat content.

Probably one of the most recent discoveries related to MFD is the biohydrogenation theory, which, according to the authors, accommodate limitations of the trans fatty acids theory. Researchers from Cornell University suggested the name of biohydrogenation theory based on the concept that under certain dietary conditions, the pathways of rumen biohydrogenation are altered to produce unique fatty acid intermediates, some of which are potent inhibitors of milk fat synthesis. Small amounts of the fatty acid named trans-10 cis-12 CLA are considered one of the main inhibitors of milk fat synthesis in the mammary gland.


Ruminal dilution rates might also be related to MFD. Shortage of water, particularly in hot summers, may affect the dilution rate in the rumen while decreasing fiber fermentation and chemical precursors for milk fat synthesis. Probably some factors that need to be re-evaluated during heat stress situations for high-yielding animals are feedline space and access to water.

Summarizing, MFD can be related to dietary fiber, intake and interactions between trace minerals, some dietary trans fatty acids and water supply. It is recommended to work with your private consultant to identify all the possible causes of this problem. Remember that any improvement in the efficiency of milk yield and its composition represent more net income and, also, lower excretion of nutrients to the environment. PD

—From Merced County Dairy Notes, October 2006

Alejandro Castillo

Dairy farm adviser with University of California Extension

Q. When should dairy producers suspect a case of milk fat depression (MFD)?

In most cases, industry detects the problem and then reports it to the producer.

Q. What should a producer do if he or she believes they may have potential MFD cases on their dairy?

They should call a nutritionist, or if they do not have a nutritionist, they should hire one.

To contact Alejandro, e-mail him at or call him at (209) 385-7403.