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Silage Harvest Takes Good Communication


Silage Harvest Takes Good Communication

By Bill Mahanna

I have had the opportunity to be on dairies from Iowa to Vermont while they were in the frenzy of chopping corn silage (with a fourth cutting of alfalfa thrown in just to make life more interesting).

This included dairy producers chopping their own silage into a dump box with a three-row, pull-type chopper to a custom harvester operating a 780 hp, 10-row chopper and filling a 15-ton truck in fewer than three minutes.

In all of these situations, the degree of kernel damage was much less than what I would term desirable as a nutritionist having to feed that silage over the next 12 months. In most of the situations, some including on-site advice of chopper manufacturer technicians, we were able to modify the chopper to produce an acceptable degree of kernel damage.

Processing Background

Kernel processing of corn silage has long been popular in Europe but did not gain much attention in the U.S. until the late 1990s with the "invasion" of European chopper manufacturers that sold machines with a roller mill as standard equipment.

Prior to that, U.S. nutritionists or chopper manufacturers did not widely advocate kernel processing for several reasons:

  • Short chop length to facilitate silage removal in then-popular tower silos already inflicted considerable kernel damage;
  • Corn silage comprised much less of the ration in most midwestern and western herds, and
  • Early research studies did not find significant milk or fat production advantages either because:
    1. the control silage had similar kernel damage or
    2. treatment rations were not adjusted to account for increased ruminal starch availability in well-processed silages (Shinners et al., 2000; Dhiman et al., 2000).

Today, with higher-producing cows demanding more dietary energy, corn silage inclusion rates have increased. In the era of $6/bu. corn, there is also an increased acceptance of later-harvest maturity (about 35-38% dry matter) to capture more valuable starch without incurring a significant loss in fiber digestibility among new hybrids with much-improved late-season stalk moisture and plant health.

To make that extra starch available to the cow, adequate kernel processing is a must. Nutritionists also have a better understanding of the rumen health benefits of lengthening the chop, but this comes with baggage as it significantly reduces kernel damage that used to occur at the cutter head.

Early on, there was much debate about what level of kernel damage was acceptable. This was complicated by the fact that there was no commonly available lab method of quantifying the extent of kernel damage or accepted guidelines as to processing standards.

This changed with research from the lab of Dr. Dave Mertens at the U.S. Dairy Forage Research Center (Ferreira and Mertens, 2005; Taysom, 2008) and the subsequent development of a standardized RoTap-based lab method (Figure and Photos) and processing guidelines (Table) jointly developed by Pioneer Hi-Bred, Dairyland Labs and Mertens.

Several commercial laboratories now offer a kernel processing evaluation test at typically less than $20 per sample.

I previously discussed new equations developed to adjust starch digestibility values based on corn silage dry matter and the starch distribution of individual silages as determined by the Ro-Tap corn silage processing scoring test (Mahanna, 2007).

While a post-harvest lab test may help explain animal performance issues and offer unbiased data to initiate a conversation with custom choppers, it does little to correct the problem once silage is in storage.

I know of one large dairy that had done such a poor job of kernel processing (less than 40% damaged kernels) that it made economic sense to purchase a stationary roller mill and re-roll all of the 2007 corn silage before putting it in the total mixed ration mixer.

To help prevent this kind of scenario and more easily evaluate the extent of kernel damage as the silage is being delivered to the bunker or silo, I have been advising dairy producers to sample several loads each hour with a 32-ounce cup, spreading the sample out and picking out every whole and half-kernel. If that number exceeds two to three kernels, discuss with the chopper operator how to improve kernel damage.

The guidelines for this field test are based upon my personal experience of observing hundreds of silages and comparing my observed kernel count with RoTap-generated lab values. I just recently sampled silages over an eight-hour period as loads were being brought to the bunker, performing both the field test and then packing the same samples off to the lab for a RoTap analysis. When the number of whole or half-kernels was fewer than three, the RoTap analysis came back in the acceptable kernel damage range of high-50% to low-60%.

I am convinced that high-60% to more than 70% damaged kernels is almost unachievable given the design of newer self-propelled choppers. This makes it critical that nutritionists start making their desires known to chopper manufacturers. I am not convinced that the current "belt-driven" approach to processing kernels is going to match particle size hurdles seen in feeds like high-moisture corn with hammer mills powered by high-horsepower tractors.

Current Recommendations

One valuable outcome of the processing debate is that it has fueled much-needed cooperative work between nutritionists and agricultural engineers. An outcome of this joint research was a paper delivered at the 2006 NRAES-181 Silage for Dairy Farms conference.

These were the concluding recommendations in a paper presented on kernel processing (Shinners et al., 2006):

  • A theoretical length of cut (TLC) greater than 3/4 in. (19 mm) raises concerns about processor life, harvester capacity, packing in the silo and fiber sorting.
  • Dairy producers should target 3/4 in. as the longest TLC with an initial processor roll clearance of 0.12 in. (3 mm).
  • If kernel breakage is not adequate, producers should consider reducing the roll clearance.
  • If plugging occurs at the processor rolls, producers should consider reducing TLC.

However, this early cooperation needs rekindling. Good data are lacking on the harvest speed or fuel consumption impact of kernel processing with high-throughput, self-propelled choppers that are common today.

Custom harvesters claim that aggressive processing slows them down (and increases fuel consumption) by at least 15%. These estimates are plausible given that data with lower throughput pull-type choppers showed that the drop from 3 mm to 1 mm clearance increased processor power requirements by more than 25%, causing the overall machine power requirements to increase 8% (Shinners et al., 2000; Shinners, 2008).

This is causing considerable dissention between custom operators who value speed and throughput to profitably run their business and dairy producers (and their nutritionists) who are increasingly demanding that kernels in corn silage look like kernels in hammer-milled high moisture corn.

Rules Change

I recently had a rude awakening as to how chopper manufacturers view nutritionists.

I visited a dairy on the East Coast that had a company technician changing the roller mill pulleys on its new self-propelled chopper to increase their differential so the kernel damage met the goals of the dairy's consulting nutritionist. I walked into the farm shop to observe the progress, and the lead technician introduced me to the other mechanic as "another one of those nutritionists!"

It is becoming clear that what nutritionists desire and what agricultural engineers assume is wanted are not in good agreement. This hit home to me in a recent exchange with Dr. Kevin Shinners, professor of agricultural engineering at the University of Wisconsin, who said on his recent trip to Germany to meet with engineers about kernel processing, the consensus among engineers was that a "nick" in the kernel was enough (Shinners, 2008).

To further reinforce this disconnect, I visited a dairy while attending the World Dairy Expo. The dairy producer (and chopper owner) pulled information from a well-known self-propelled chopper manufacturer web site to answer my question about the revolutions per minute speed differential of the roller mill. The web site information (last updated May 12) told us the answer, but upon further reading, it referenced "scuffing" the kernels and stated that "while the skin of the kernel needs to be cracked, it does not have to be pulverized."

Most nutritionists I talk to would like to see all of the kernels pulverized to a similar micron size that is demanded from high-moisture or dry corn sources. I THINK it is our responsibility as nutritionists to explain to custom choppers and their equipment suppliers why we want more kernel damage than in the past, including:

  1. a higher cost of supplemental corn,
  2. increased intakes and rate of passage in today's high-producing cattle and
  3. a possible link between undigested starch and problems such as hemorrhagic bowel syndrome.

We need to point out to them the particle size in the high-moisture and dry corn as an example of our desire for finer (and more uniform) starch and, perhaps, go so far as to have examples of corn silages to show them what is an acceptable versus unacceptable level of kernel damage.

RoTap sieves specifications.
The RoTap laboratory instrument shown above standardized the measurement of kernel damage. The photo below shows the RoTap sieves in relation to a penny.

Questions to Ask

It is becoming clear to me, after discussions with chopper as well as roller mill manufacturers, that there are many factors that contribute to kernel damage (Zumbach, 2008; Horning, 2008; Sherer, 2008). Inquiring about the chop length, roller mill wear and roller mill gap is only a start.

RoTap kernel damage guidelines.

It is important that we ask and begin to track answers to these questions:

  1. What is the roller mill differential? Typically, it should be 10-30% for corn silage and 40% for snaplage, with the higher differential causing more aggressive damage but also contributing to problems with "burning belts."
  2. What is the roller mill design? Sawtooth design, like what is used to process oilseeds, is becoming popular.
  3. How many teeth per inch? Choppers have roller mills of different diameters, so teeth per inch is the preferred metric; three to five teeth per inch is standard for corn silage and finer yet if harvesting snaplage.
  4. Is there a roller mill teeth differential? Having the faster roll a coarser cut (three to four teeth per inch) and the slower roll a finer cut (five to six teeth per inch) allows for more aggressive pulling of the silage through the mill and often allows for a wider gap to achieve similar levels of kernel damage with less tendency for roller mill breakdown.

The Bottom Line

The need to rapidly harvest increasingly large acreages of silage along with increasing grain prices and the challenges of meeting energy needs of high-producing cows have somewhat polarized the chopper manufacturing/custom harvester industry and the nutritional community. It is clear that many factors influence the extent of kernel damage, but there seems to be a lack of communication as to how best to meet the needs of both camps.

We have to resolve this and arrive at a win-win solution so the custom chopper can maintain profitability and continue to provide a much-needed service while delivering dairies the level of silage processing needed to help nutritionists lower ration costs so the dairy producer remains profitable as well.


Dhiman, T.R., M.A. Bal, Z. Wu, V.R. Moreira, R.D. Shaver, L.D. Satter, K.J. Shinners and R.P. Walgenbach. 2000. Influence of mechanical processing on utilization of corn silage by lactating dairy cows. J. Dairy Sci. 83:2521- 2528.

Ferreira, G., and D.R. Mertens. 2005. Chemical and physical characteristics of corn silages and their effects on in vitro disappearance. J. Dairy Sci. 88:4414-4425.

Horning, M. 2008. Horning Manufacturing LLC. Personal communication.

Mahanna, W.C. 2007. Feed particle size key in cow, lab. Feedstuffs. Aug. 13. p. 11.

Sherer, B. 2008. Scherer Corrugating & Machine Inc. Personal communication.

Shinners, K. 2008. University of Wisconsin- Madison. Personal communications.

Shinners, K.J., D.R. Mertens and J. Harrison. 2006. Processing whole-plant corn silage: Machine, storage and animal perspective. NRAES-181 Silage for Dairy Farms Conference. Jan. 23-25. p. 140-157.

Shinners, K.J., A.G. Jirovec, R.D. Shaver and M. Bal. 2000. Processing whole-plant corn silage with crop processing rolls on a pull-type forage harvester. Applied Engineering in Agriculture. 16(4):323-331.

Taysom, D. 2008. (Dairyland Laboratories, Inc..)

Zumbach, J. 2008. Krone-North America. Personal communication.


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