Nutrition: Stretch starch

October 25, 2010 10:33 AM

Bonus Content

Spanish translation

Manure washing

Grain processing

Starch test

*Extended comments are highlighted in blue.

Corn prices appear to be bullish in 2011, with future prices more than $5/bu. ($179/ton), increased production of ethanol and strong corn export markets.

Yields have also been disappointing, with wet conditions in the spring and heat stress in August reducing yields and wide ranges between fields and within fields. Yet one fact remains: High-producing dairy cows need rumen-fermentable carbohydrate for optimal production of amino acids and energy as volatile fatty acids. The table below lists target values, with starch a key focus.

The suggested starch level ranges from 22% to 26% in the total ration dry matter depending on corn particle size, level and source of forage, level of fiber (neutral detergent fiber, acid detergent fiber or lignin) and feed intake. An on-farm situation with lower levels of starch (22% to 24%) could include high levels of corn silage (more than 50% of the total forage dry matter in the ration), wet rations (more than 55% moisture), rumen-available starch (dry corn less than 900 microns or high-moisture corn more than 30% moisture), high dry matter intakes (more than 4% of body weight), lack of long fiber (less than 50% on the top two in the Penn State Particle Box), higher levels of Rumensin (more than 350 mg per day), and/or higher levels of unsaturated oil (more than 1 lb. of vegetable oil or ½ lb. of “free oil” such as distillers’ grains or extruded soybeans, where the oil is not contained in the seed form).

DT 031 D10081 A00588

Kernel or plant processed corn silage exposes the starch to rumen microbial fermentation. All kernels should be damaged or broken, especially with corn silage of more than 35% dry matter. Not seeing any whole kernels can be a goal. Corn silage stored more than three to four months also increases starch degradation in the rumen. Grain processing guidelines are as follows:

  • Grind dry corn grain to 900 to 1,100 microns.
  • High-moisture shelled corn should contain 25% to 30% moisture, high-moisture ear corn 28% to 32% moisture, and snaplage/earlage more than 35% moisture.
  • Steam-flaked corn should range from 24 lb./bu. to

26 lb./bu. to optimize gelatinization of starch.

University of Pennsylvania researchers published a formula to predict total tract starch digestibility using fecal starch and lignin and ration starch and lignin. The lignin was used as a marker to estimate starch utilization.

The researchers concluded that for each increase in fecal starch (for example, from 6% to 7%), the potential loss in milk yield was 0.7 lb./day. Cumberland Valley Analytical Services analyzed 1,420 fecal samples with starch content ranging from 0.20% to 38.9%, with 62% of the samples containing less than 5% starch.

The cost of fecal starch analysis is $15 to $20 per sample. Pool fecal samples from 10 to 15 cows and submit a mixed sample, requesting fecal starch.

Washing manure through a screen (six to eight squares per inch) allows the dairy manager to quickly "see" if corn processing was optimal. Take a cup of fresh manure (400 to 500 grams) and wash it with a stream of warm water through the screen, flushing out digested material.

It typically takes about 30 seconds if your screen has sides that allow for more water pressure. Look at the remaining grain particles. Pieces of barley or corn grain with white starch remaining indicate that some feed value was lost.

If the seed pieces are hard, additional grinding or processing may be needed to expose the starch to rumen microbial fermentation or lower gut enzymatic digestion. Corn kernels in the feces from corn silage reflect that the seed was too hard for digestion and not chewed by the cow.

Mature and dry corn silage can cause this result, as grain is hard. Some corn silage varieties can be selected for softer kernels, allowing for more digestion.

The Cargill Manure Separator is commercially available from NASCO ($250 plus shipping and handling), or a separator can be made from an 8" screen framed in a wooden box.


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