The author is an associate professor and dairy management extension specialist with Virginia Tech University.

Gonzalo Ferreira
Several scientists have contributed enormously to the dairy industry during the past 50 years, and Dave Mertens might be at the top of the list. If you still need convinced of this reasoning, I invite you to consider the following question: Have you ever submitted a forage sample to a commercial laboratory to be analyzed? If the answer is “yes,” then it is likely Mertens’ work on forage analysis and dairy cattle nutrition helped guide which forage quality metrics are on the report and how they are derived.

During the 2022 annual meeting of the American Dairy Science Association, a symposium was held to recognize the contributions of Dave Mertens to the dairy industry. The following are some highlights of his influence on feed analysis.

Fiber analytics

The concentration of digestible energy of a feed is mainly determined by the concentration of fiber in the feed. This means that forages containing greater concentrations of fiber have less energy than forages containing lower concentrations of fiber. This relationship is explained by the fact that fiber is incompletely and nonuniformly digested by cattle. Conversely, the nonfibrous components of a feed are almost completely and uniformly digested by cattle. The message here is that the more fiber the forage has, the lower its energy content.

Before we get into the specific contributions of Mertens, it is important to offer some definitions. Let’s start by describing “fiber.” From a botanical perspective, fiber includes the structural components that support and give strength to the plants, and these components include pectin, hemicellulose, cellulose, and lignin, which are all contained in the cell walls.

From a ruminant nutrition perspective, fiber includes the structural components of the cell walls that are slowly digested in the rumen of the animal and only by the action of microorganisms in the rumen. These components include mostly hemicellulose, cellulose, and lignin of the cell walls (pectin is excluded). These three components are included in a term known as neutral detergent fiber, or NDF. Putting the pieces together, the next take-home message is that when the NDF concentration of a forage increases, the energy concentration typically declines.

Inherent lab variability

In a forage laboratory, there are two major types of analytical procedures: theoretical and empirical. For theoretical procedures, a pure standard of the analyte exists — for example, a mineral like calcium or a specific molecule like glucose. In these theoretical procedures, you can subject a known amount of pure standard to analysis and assume success on the technique when the laboratory measures or “recovers” the total known amount.

In contrast, a pure standard does not exist for empirical procedures. The NDF procedure is an empirical method subjected to differing or misleading results depending on how the analysis is performed. There is no way to determine if a laboratory is running the analysis properly. This problem led to the challenge of developing a procedure by which laboratories can ensure they are performing the NDF analysis correctly.

Enter Dave Mertens

In the early 1990s, no official method had been approved for determining the concentration of NDF in animal feeds, and this void gave laboratories license to modify the method arbitrarily, resulting in great variability in NDF concentration among labs. In addition, the lack of an official method was impeding commercial laboratories to obtain certification.

To directly tackle this problem, Mertens developed a research program at the USDA-ARS Dairy Forage Research Center in Madison, Wis., and fine-tuned the NDF procedure to reduce variability among laboratories. This procedure, known as the amylase neutral detergent fiber (aNDF) method, later became the reference method utilized by the National Forage Testing Association to certify commercial laboratories in the U.S. and around the world.

Mertens’ procedure was later accepted by AOAC International (formerly, the Association of Official Agricultural Chemists) as the official method to determine the concentration of fiber in all types of animal feed. In 2003, Mertens was awarded the Collaborative Study of the Year Award by AOAC, which stated, “This study is deserving of this award for its complexity and impact on the international agricultural community. The method truly deserves to become the much-awaited international standard for the determination of neutral detergent fiber.”

Mertens’ impact on the dairy industry is truly remarkable. Any ruminant nutritionist knows that at least two things are needed to formulate a ration, and these are knowing the nutritional requirements of the animals to be fed and knowing the nutritional composition of the feeds. The latter means that thousands of farmers and millions of cattle have been directly impacted by Mertens through forage testing for feed evaluation or in the ration formulation process.

To add further perspective, two of the commercial laboratories certified by the National Forage Testing Association have reached more than 8,683 stakeholders within the U.S. and 1,820 stakeholders throughout 49 countries since 2015. Also, through his work with the National Forage Testing Association, Mertens has contributed to the certification of at least 99 laboratories within the U.S. and 38 laboratories around the world.

Mertens has dedicated a great part of his career to improving laboratory techniques that have a direct impact on ruminant nutrition and cattle farming systems. For those who believe that being a scientist and working in a laboratory might be too far from having impacts on the farm, I invite you to remember Dave Mertens the next time you submit a forage sample for analysis.


This article appeared in the November 2022 issue of Hay & Forage Grower on page 22.

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