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Did you harvest optimal rumen starch digestion?

Courtney Heuer and John Goeser Published on 02 January 2015

With the turn of the new year, most dairy and beef producers are feeding last fall’s harvest of high-moisture corn, corn silage and other cereal grains. But let’s think back to when these high-starch forages and grains were planted and harvested to understand if you really captured every bushel of corn in your corn silage or high-moisture corn.

Consider this: 20-ton-per-acre corn silage with 35 percent starch yields about 100 bushels of corn. In many cases, with poor rumen starch availability, this “100 bushel” corn silage can actually feed like 70- bushel corn silage.

Would you rather harvest 100 or 70 bushels of corn silage? Capturing all 100 bushels relies on optimizing rumen starch digestion, and many factors affect starch digestion both pre-harvest and post-harvest.

Before talking potential, let’s recognize that corn silage is now the predominant forage fed to dairy cows, and it feeds differently (and better, many times) while offering consistency and yield relative to other forages because of the grain.

Corn-silage starch ends up being a vital source (up to 50 percent) of dietary energy to lactating dairy cows as well as beef cows. Yet rumen and total-tract (rumen and intestine) starch digestion varies substantially.

There may be 5 to 7 pounds performance difference in the same TMR (e.g., same nutrient composition but new-crop versus old-crop silage and high-moisture corn caused by different starch digestion). Determining rumen-available starch load is difficult but crucial in determining the amount of nutrients actually available to the animal.

Considering factors that affect available starch load prior to harvest, what hybrids were planted? Genetics, as well as environment, have a substantial impact on starch availability at harvest. Grain hardness is a heritable genetic factor, with hard grain leading to less rumen digestion.

At harvest, how mature was the plant? What was the moisture level? Moisture and maturity often go hand-in-hand. As the plant matures, the dry matter and grain hardness increase; a more mature plant will have greater prolamin content, which is a protein that encases the starch like a steel cage.

The prolamin protein buildup results in the starch being guarded from rumen microbes to access, leading to lower rumen starch digestibility. While grain hardness increases with certain genetics and advanced maturity, the hardness effects can be somewhat alleviated through extensive grinding or kernel processing and fermentation.

So how well was your crop processed? The kernel-processing score goal is to achieve greater than 65 to 70 percent (of starch passing through a 4.75-mm screen).

Grinding high-moisture corn to less than 1,500 microns is preferred, depending on moisture and assuming adequate fermentation. In dry corn, striving for a less-than-650-micron grind size is ideal.

In periods where we may have not hit our processing goals, some have opted for re-grinding at the silo (e.g., hammer mill previously ground but poorly processed or fermented corn) to increase rumen starch digestion and gain milk.

There are also digestive enzyme products that can help break down starch; however, users should make sure published research backs the enzyme product claims. Processing and enzymes work by increasing the starch (grain) surface area that rumen microbes can attach to and break down. Steam flaking is another option to open up the grain and starch.

Next, how long was the crop allowed to ferment prior to feeding? With wet springs that lead to late planting, drought or early snowfall, sometimes we don’t have ideal conditions for yield or to harvest optimal rumen starch digestion from feeds.

But consider building up your inventory that will, over time, allow you to feed forages that are always fermented 90 days or longer and skip a period of low rumen starch digestion. Managing both processing and fermentation will help optimize the starch available for your dairy cattle to use as energy.

After picking the best genetics, managing maturity, processing and fermentation, and coping with the environment (which can account for 50 percent or more of feed quality), how can we assess the resulting feed’s potential? The answer partly lies in rumen starch digestion measures.

Commercial laboratories use the University of Wisconsin (UW) feed grain evaluation system (v2.0) to check grain quality or rumen starch digestion techniques to gauge feed starch potential.

When measuring rumen starch potential directly, both rumen in vitro (simulated, completely removed from the animal) or in situ (incubates feed within the rumen of cows) can be valuable tools to check if we’re capturing all 100 bushels per acre from our corn silage.

Regardless of the technique used, the aim is to forecast what your cows can actually do with corn and corn silage in the TMR.

Rumen starch digestion benchmarks

Figure 1 shows TMR benchmarks that we can aim for based upon published meta-analyses that studied dairy cattle rumen starch digestion.

Rumen and total tract TMR

The goal is to achieve greater than 80 percent rumen starch digestion in dairy cattle while balancing total starch load to avoid acidosis. Individual feed starch digestion results from our team, estimated using rumen incubation techniques, are listed in Table 1.

By determining the rumen-available starch in your feeds early in the year, you will be able to track the progress in starch digestibility over the feedout. As the year goes on and fermentation improves rumen starch digestion, you can measure this against your goals.

With adequate processing or fermentation over time, you should expect to see starch digestibility increase 10 to 20 points. This will allow you to get more energy out of the same feeds.

Hitting the rumen starch digestion benchmarks allows you to capture all 100 bushels. This type of increase in starch digestion over average will lead to as much as 10 pounds of milk per cow through increased energy and microbial protein synthesized.

While you reflect on your past year’s harvest and what could have been altered to help increase rumen starch digestion in your feeds, know that there are still options now that have been discussed here. It can also help you look ahead to next harvest season and figure out how you can achieve your goals for optimal rumen starch digestibility.  FG

John Goeser is an adjunct assistant professor at the University of Wisconsin – Madison and animal nutrition director at Rock River Laboratory, Inc. 

References omitted due to space but are available upon request. Click here to email an editor.

Courtney Heuer
Research Coordinator
Rock River Laboratory Inc.