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Starch and fiber digestibility: A balancing act

Phil Krueger for Progressive Dairyman Published on 07 August 2017

Consistently achieving high milk production requires performing a balancing act. The goal is to produce the most milk with the greatest market value possible for the least cost. The cornerstone of most rations supporting high production while maintaining excellent animal health is high-quality forage.

Along with high-quality forage, supplemental sources of digestible fiber, proteins and starches are keys to balancing the cow’s dietary requirements. Producers who grow the majority of their feedstuffs must allocate use of those assets to the cattle groups that can utilize them economically while meeting the logistical needs of the dairy.



Feed is the number one milk production cost. Dairy producers who generate more feed value from forages can typically lower their supplemental starch and byproduct usage, which can lower the cost of milk production.

Achieving better feed efficiency and, more important, a higher income over feed cost not only gives producers more return on investment but also creates peace of mind that their crop plans and feeding programs are successful.

Building the foundation in the field

Providing the right mix of nutrients to the cow is critical, and it starts in the field. Dairies can help keep input costs under control by growing high-quality forages and starches in the necessary quantities that will support optimum milk production. Herd health and the economic vitality of the operation depend on it.

The first step focuses on hybrid selection. A corn silage hybrid that provides a good balance of digestible fiber and starch can help an operation save money on supplemental grain while providing the highest-quality and most efficient forage option.

Although corn prices have come down, it’s still more economical for producers to grow the bulk of their forages and grain, if possible, rather than purchasing feedstuffs.


Growers should select hybrids based on the nutrient needs of the animals they’re feeding while also taking into account the agronomic limitations of their fields and growing conditions on their farms. Producers should sit down with their agronomist and nutritionist to build a crop plan this fall that makes sense for their fields, their management and their feed storage abilities.

The benefits of balanced fiber and starch in the ration

To boost milk production and help ensure animal health, dairies need to balance fiber and starch digestibility in the diets they feed. It’s like walking a tightrope. On one hand, too much fiber, especially hard-to-digest fiber, leads to lower dry matter intake, which limits milk production. On the other hand, too much rapidly digestible starch can lead to acidosis and other problems, impacting herd health and inevitably curbing production.

For peak performance, a cow must digest fiber at a high rate in the rumen with just enough starch digestion to maximize rumen microbial yield. Rumen microbes digest the forages and fibrous products in rations and use those nutrients to increase their own populations.

Once they pass out of the rumen to the small intestine, they die, are digested and become nutrients for the cow to utilize for its own needs, which is primarily the production of milk. The amino acid profile of rumen microbes is considered the ideal fuel for milk production. High-quality forages yield more rumen microbial growth than poorer forages, which ultimately reduces diet costs.

Corn hybrids bred primarily for grain or that have a harder kernel contain a higher percentage of lignin, which is indigestible fiber that stays in the rumen longer and leads to decreased feed intake.

This, in turn, limits milk production. To combat high levels of indigestible fiber, producers must limit the amount fed and likely will need to supplement digestible fiber sources or feed more starches, which increases diet costs.


Some dairies attempt to alleviate this problem by raising the chopping height of their corn silage, which lowers tonnage per acre but increases starch concentration, making silage difficult to feed at high rates. Cows are designed to digest fiber. Anything we feed them that reduces fiber digestibility typically increases diet cost.

BMR hybrids, bred specifically for use as corn silage, contain less lignin. Therefore, more fiber in a BMR hybrid is easily digestible. Such hybrids offer greater neutral detergent fiber digestibility and move through the rumen more quickly, making way for the next meal.

This means greater dry matter intake and better feed efficiency but also more nutrients digested and utilized from a feedstuff that costs less than supplements.

Fiber digestibility is just one side of the coin. Dairy producers also must employ tools to increase the digestibility of the starch – the kernels – in their corn silage. Currently, there are some small differences in kernel texture among corn hybrids. But the primary opportunities to increase starch availability are kernel processing and allowing the silage to ferment four months or longer before feeding.

Well-processed kernels are key to obtaining optimum starch digestibility in corn silage. Under-processed kernels will move through the animal undigested, wasting a valuable energy source. Over-processed corn silage, at times when the fiber particles are smaller than ½ inch, can lead to acidosis if the operation does not provide supplemental effective neutral detergent fiber in the ration.

Striving for a ¾- to 1-inch theoretical length of cut will normally eliminate the potential effects of over-processing on the fibrous portions of the silage. Therefore, producers should work with their nutritionists to continually monitor and test corn silage and make adjustments to the ration. This attention to detail can keep milk production on target as conditions inside the bunker change.

Managing and adjusting dairy cow rations

Once an established crop and feeding plan are in place, dairy producers need to continually fine-tune rations and feedstuff options to ensure optimum cow performance and positive return on investment.

A knowledgeable nutritionist and a good software program can help producers understand the nutrient value in their inventories. These tools are essential for mixing and matching ingredients to produce a ration that is functional and economical, and produces the most milk for the lowest cost.

A dairy producer should consult with a nutritionist every two to four weeks, perhaps more often in the fall or when changing from an old to a new crop.

Dairy producers who plan their crop with an eye on optimizing milk production can produce the tonnage and quality they need to formulate high-quality rations for their cows. This will give them the tools to adjust to the cows’ needs and provide a diet that leads to higher milk production and greater profits.  end mark

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