Corn kernel condition a key to starch digestibility

Ray Mueller
Now Media Group


Want to get the best milk production from one's dairy cows or to feed the wild turkeys when manure is applied on agricultural land?

That's how Rock River Laboratory animal nutritionist and research and innovation director John Goeser framed a question to attendees at the 2016 annual meeting of the Sheboygan County Forage Council. He was referring to how much of the starch in corn silage and shelled corn is not digested by dairy cows and is therefore lost in the manure rather than being converted into milk production.

Dairy margin data

With dairy margins have turned very tight during the past year and most likely remaining that way well into 2016, that point deserves extra attention. Goeser said tests of manure for fecal starch (about $20 per sample) and a sieve test of corn kernels for particle size are two practical ways to diagnose starch waste during digestion.

From 2004 through 2015, dairy margins — the difference between milk prices and feed costs — ranged from a plus $8.50 to a minus $4.60 per hundred of milk produced, Goeser pointed out. He believes dairy farmers can produce extra milk with the same cow numbers and boost their chances for profits or at least reducing negative margins by being aware of how important the efficient use of starch by dairy cows is.

Digestion percentages

Based on the premise of 10 pounds of potentially available starch in the daily ration for a dairy cow, Goeser likes to see that at least 70 percent of it is digested in the rumen and that a great portion of the remainder is digested by the intestine. While digesting 6 of those 10 pounds in the rumen is close to the average, the actual number can range from 3 to 9 pounds, based on the physical condition of the starch.

If the difference is 6 of those 10 pounds, only 3 instead of 9, it can easily translate into a 30-pound per day difference in milk production by a cow, Goeser remarked. Even at a more normal difference of 3 to 5 pounds of milk per day based on starch digestion, the 3 pounds would convert into 45 cents daily per cow at today's milk prices.

Based on Rock River's laboratory test results, having 8.5 of the theoretical 10 pounds of starch in a daily ration digested in the rumen should result in 3 more pounds of milk per day per cow compared to digesting only 6.5 of those pounds, Goeser said. A good ration would have a combined 50 percent of sugars and starches to provide a dairy cow with sufficient energy.

Fecal starch testing

As was the case at an earlier speaking appearance in neighboring Manitowoc County, Goeser learned that no dairy farmer in his audience was having fecal samples tested for starch content. Failure to do so is missing out on a good opportunity.

In the recent fecal starch tests done at Rock River Labs, the usual range of starch in the fecal matter is 2 to 10 percent, meaning that on average, 95 percent in the manure is material other than starch compared to 90 percent in 2011, Goeser said. He considers 98 percent to be the gold standard for that statistic.

From another angle, Goeser used these numbers: corn silage yielding 20 dry matter tons per acre would have 100 bushels of grain or about 35 percent starch in each ton. A poor rate of starch digestion when feeding 27.5 tons of corn silage per day to a herd of 1,000 dairy cows could result in a daily loss of up to $1,000 in potential income or $365,000 per year, he calculated.

Corn characteristics

In large degree, the problem with the starch digestibility of corn by ruminants is due to corn breeding and genetics that were geared to preserving the physical integrity of the grain during handling, storing and shipping, Goeser said. 'It needed hardness when hitting steel.'

Having a protein protector act like a cage around the starch in a corn kernel also serves to nurture plant growth, Goeser observed. But that protective outer shell is not conducive for digestion of the starch by cattle.

To counteract that, kernel processing was adapted to break or crush the kernels as corn silage was being harvested, he said. But 'it takes more than a nick' of a kernel, especially with high moisture or dry shelled corn, to make the starch readily available.

Corn silage tips

The moisture in corn silage helps to soften the kernel, but that is not always a satisfactory solution, Goeser remarked. Nonetheless, he prefers that corn silage be in storage for at least three months before it is fed.

Goeser suggested harvesting corn at 65 percent moisture for storage in bunkers and at somewhat different percentages for other types of storage in order to prevent seepage. To a question, he said that letting corn get more mature before harvest for silage to obtain more starch should not be done because doing so would be more than offset by setbacks to proper fermentation.

At the time of corn silage harvest, an easy and no cost test is the floating bucket of water that involves the placement of silage samples to separate kernels and fodder, Goeser explained. This could lead to adjustments on the harvesting equipment if the kernels are not properly broken.

On a question about the effects of plant diseases on corn silage, Goeser said they are not likely to affect fermentation, but feed quality can be affected because the diseases could be linked to the growth of fungi, molds and yeasts. He strongly endorsed the use of an inoculant such as lactobacillus buchneri to support good fermentation.

Kernel particle size

With both whole kernel corn and the kernels in silage, Goeser strongly recommended a particle size of less than 4.75 millimeters for at least 70 percent of the kernels. He noted that there is a sieve tester available for doing this but warned it is very noisy.

Of the testing which has been done, there has been an improvement of having 50 percent of the samples meet that standard in 2013 to about 60 percent more recently. Of the corn silage samples, however, 50 to 60 percent are not meeting the 70 percent standard for kernels being smaller than 4.75 millimeters.

Responding to a question, Goeser said it is 'not possible' to grind corn into 'too fine' a size. He added, however, that the cost of grinding it to an extremely fine form is not justified and suggested that the 70 percent at less than 4.75 millimeters is adequate.

County samples

To give that test a local look, Sheboygan County Extension Service crops and soils agent Mike Ballweg visited six dairy farms in the county during the coldest day in January to collect samples for testing at Rock River. The results showed a range of 37 to 78 percent meeting the 70 percent standard for 4.75 millimeters. Two of them were very close to 70 percent.

When asked if there are any corrective measures for corn kernels not meeting the standard, Goeser said they are limited at the moment to ration changes, the possible use of some enzymes and longer periods for silage fermentation.

For the longer term, Goeser listed education on actual starch digestion, changes in corn genetics, grower selection of those genetics, monitoring of kernel processing effectiveness and dairy herd management to take full advantage of the potential of starch for milk production.

He can be reached at (920) 261-0446 or by his name on Twitter.