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Fecal starch: Are you missing out on energy?

Aimee N. Hafla for Progressive Cattle Published on 24 December 2021

The USDA price forecast for corn for 2021-22 continues to remain higher than we have experienced in the previous few years, thanks in part to a significant demand from China in addition to tight domestic demand.

Feeding cost of gain is sensitive to corn cost, and the Focus on Feedlot report generated by Kansas State University reported an average cost of gain for steers in July of 2021 to be $103.52 per hundredweight (cwt) compared to $82.61 per cwt at the same time in 2019. This increase in the average cost of gain is a result of the greater cost of corn and other energy feeds.

The energy component of feedlot rations accounts for 50% to 90% of the diet dry matter and is primarily comprised of starchy cereal grains like corn, barley and wheat. Finishing cattle diets often contain as much as 40% to 60% starch as a percent of total diet dry matter. Starch is a nutrient that packs a big punch when it comes to providing energy to the animal to drive bodyweight gain. Residual starch in the manure can be an indicator that dietary energy is being wasted. With the cost of energy commodities remaining high, it may be worthwhile to evaluate fecal starch concentration on your yard.

A survey of Midwestern feedlots conducted in 2014 reported a large variation in both degree of dry-rolled and hammer-milled corn processing and the resulting levels of fecal starch from cattle consuming finishing diets. The average fecal starch reported on feedlots in this survey was 19%, with a range of 7% to 37%. Furthermore, a Canadian study found fecal starch on feedlots using barley as their primary energy source averaged 10%. These relatively high levels of fecal starch suggest there are opportunities industry-wide to improve animal performance and feed efficiency through increased starch utilization. A fecal starch value of less than 3% is the ultimate goal. If fecal starch is greater than 5% (depending on level of grain processing), there is likely opportunity to improve starch digestibility.

Several management and dietary conditions contribute to the degree of starch digestibility in a feedlot diet. Starch digestibility in the diet is most affected by:

1. Extent of grain processing: Processing of grains increases starch digestibility. Whole corn may have a total tract starch digestibility of only 80%, whereas steam-flaked and high-moisture corn may have starch digestibility as high as 98%.

2. Kernel processing of corn silage: Just like grains, processing of corn silage kernels during harvest increases starch digestibility. Kernel processing enhances kernel breakdown by increasing surface area available for bacterial and enzymatic digestion. Research published in the Nebraska Beef Cattle Report in 2018 reported that backgrounding and growing steers consuming diets with silage that was kernel processed demonstrated a 2.9% improvement in feed efficiency compared to steers consuming the same diet with unprocessed corn silage.

3. Moisture content of grain and fermented feeds: Corn silage that has a higher moisture content is likely to have a greater starch digestibility, compared to drier corn silage (less than 35% moisture).

4. Fermentation: Starch digestibility increases with time in storage, in both corn silage and grains. A quality fermentation process and use of a forage or grain treatment product will enhance the extent of improvement in starch digestibility as the feed is stored.

5. Type and variety of grain used: Wheat, barley and corn have extensive ruminal starch digestibility, while sorghum grain tends to have lower starch digestibility. Some varieties of corn have better starch digestibility compared to others.

6. Synchronization of protein and starch in the diet: Lack of balance between available carbohydrates (particularly starch) and protein available to the rumen microbes (specifically soluble protein) limits the ability of the microbes to use the energy provided to them. Research conducted at the University of Minnesota demonstrated that cattle performance was enhanced when urea was added to finishing diets that were already adequate in crude protein (CP) content, as supplied by dry distillers grains. The improvement in animal performance was attributed to an increased proportion of degradable protein available in the high-grain diet.

Beyond management considerations, feed enzyme products can be used to enhance starch utilization in feedlot cattle. There are many commercially available enzyme products for ruminants, but in the case of feedlot diets it is important to focus on products that contain amylases, which are proteins that break down starch.

In a recent farm trial conducted at a feedlot in England with Holstein-Angus cross fat cattle, it was found that the manure of the cattle receiving a starch-digesting enzyme product had less leftover starch (3.8% versus 4.8% starch, respectively) compared to cattle not receiving the enzyme. The increase in starch utilization demonstrates greater nutrient digestion and absorption. Enhancing nutrient availability and absorption of feedstuffs should result in greater live bodyweight gains and improved feed efficiency.

Talk to your nutritionist about ways to improve starch utilization, especially in diets utilizing a significant amount of energy commodities. If a laboratory test is not available, visually assess the manure to see if a significant amount of corn is passing through the animals. If the corn is readily apparent in the manure, then you need to ask yourself if your cattle are missing out on energy.  end mark

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

Aimee N. Hafla
  • Aimee N. Hafla

  • Beef Cattle Nutritionist
  • Agri-King Inc.
  • Email Aimee N. Hafla

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