Farming Magazine - July, 2013


Forage Harvest Guidelines

Something old, something new
By Everett D. Thomas

Corn processed with a Shredlage unit results in silage that has longer particle length than regular processed or unprocessed corn silage.
Photo by Roger Olson.

The "something old" refers to forage harvesting equipment, including mowers and forage choppers both with and without silage processors, while the "something new" refers to Shredlage, which is actually a different form of corn silage processing. It's always exciting to look at farm equipment, especially implements that are "new and improved," as the ad agencies often claim. We'll look at both new and not-so-new forage harvesting equipment, with the emphasis on proper setup and operation.

Mowing and managing hay crops in the field

Disc mowers and mower-conditioners have almost entirely replaced sickle bar mowers, and for a couple of reasons. (I'll refer to mowers and mower-conditioners interchangeably for simplicity's sake, but will comment on this later.) The first and foremost reason for the change is speed, especially when there's a considerable amount of grass in the stand.

Sickle bar mowers are notorious for plugging if they're operated too fast for field conditions. In well-fertilized, first-cut grass fields, it wasn't unusual to see farmers creeping along at 3 mph or less, even with time at a premium. At the opposite end of the scale, there's no reasonable limit on how fast a disc mower can be operated, with the speed depending on the evenness of the field and the bravery, or foolishness, of the operator.

The second reason for the move to disc mowers is that compared to sickle bars, there's less downtime for repairs. Hit a stone or scalp the soil with a sickle bar mower and repairs are often necessary to replace one or more knife sections. However, it takes a fair-sized stone to put a disc mower out of commission. The result is that not only do disc mowers get the job done quicker because of operating speed, but there's less time spent on repairs.

Farmers quickly realized these advantages, and their sickle bar mowers started gathering rust in their equipment "boneyard" or in the back corner of farm equipment dealer lots.

Once farmers discovered that disc mowers were more resilient, it didn't take long for them to start mowing fields closer to the soil surface. This was done at the recommendation of some state university agronomists, with the suggestion to mow alfalfa at a 1 to 2-inch stubble height. Alfalfa quality suffers a bit, since the bottom of the alfalfa plant doesn't contain many leaves, but total yield increases by enough to more than make up for this - at least as far as farmers are concerned. Over the course of a typical season, alfalfa yield increases by about 500 pounds per acre for each inch of reduction in stubble height.

Since grass quality is similar from top to bottom, closer mowing seems to be a clear winner. Well, almost: Mowing too close means occasionally scalping the soil surface, which damages alfalfa crowns and can also result in contaminating the forage with soil and other surface debris.

Should you condition hay crops? Some research on the use of conditioners in hay crop silage found that as long as the windrows were spread out to at least 75 percent of cutter bar width, conditioning didn't result in any increase in the drying rate of alfalfa.
Photo by Everett Thomas.

It's no coincidence that the ash concentration in hay crop silages started increasing right along with farmers' use of disc mowers. As some farmers realized this, they backed off a bit on mowing height, but not all of them have, and average ash concentrations remain well above what they were before the advent of disc mowers. A slight increase in ash may be an acceptable tradeoff, but not when levels are in the 15 to 18 percent range, as we occasionally find. Since "internal" ash - representing the nutrients inside the plant, including potassium, phosphorus, calcium, etc. - averages 8 percent, a forage analysis showing 18 percent ash means that for every 10 pounds of hay crop dry matter fed, there's actually 9 pounds of forage and 1 pound of contaminant. So, while it's OK to mow fields a bit closer, "too close" can lead to problems both in the silo and in the cow.

The other problem is that mowing grasses at a 1 to 2-inch stubble height removes some of the nutrients the plants need for the next crop. Therefore, mowing alfalfa grass at a 2-inch stubble height or less is OK for the long-term health of the alfalfa, but not for any forage grasses in the stand.

Mowers versus mower-conditioners

A hay crop conditioner either crushes or otherwise damages forage stems, increasing the rate of moisture loss. The two common types of conditioners are double rollers of various designs, and impellers that rotate to abrade the stems. There's a considerable difference of opinion on which type is best, but most research suggests that rollers are preferable for alfalfa and clover, while impellers may do a better job on grasses.

For farms with both species, my preference is rollers, because impellers can be alfalfa leaflet removal tools. Manufacturers of impeller conditioners claim that if operated properly, this doesn't happen, but at least two university trials have found higher alfalfa leaf losses with impellers than with rollers. One trial in Italy found that alfalfa hay that had been conditioned with impellers had 1 percent lower crude protein than alfalfa hay (cut at the same time and from the same field) that was conditioned with rollers.

Do we need to condition hay crops? Some research on the use of conditioners in hay crop silage found that as long as the windrows were spread out to at least 75 percent of cutter bar width, conditioning didn't result in any increase in the drying rate of alfalfa. Until we learn more, we should continue to condition forages that are to be harvested as dry hay, but it's probably not necessary to condition hay crops harvested for silage - as long as they're managed in wide windrows. Note the words after the dash!

Processors for corn silage

In processed corn silage, chopped forage has been passed through corrugated rollers that crush kernels, cobs and stover. Some farmers call these units "kernel processors," but that's a bit of a misnomer, since everything passing through the rollers is impacted. In fact, the most obvious difference between processed and unprocessed corn is the absence of large pieces of cob that cows often sort out of the feed bunk.

This is the case even though most processed corn silage is chopped at a 0.75-inch theoretical length of cut (TLC), compared to the typical 3/8-inch TLC for unprocessed corn silage. Silage processing done right not only breaks almost every corn kernel, but reduces cobs to kibble-sized pieces. The result is that the ration the cows actually consume is closer to what's put in the feed bunk.

Some comments about the words "done right" in the preceding paragraph: Correct adjustment of silage processor rolls is critical. The normal roll spacing ranges from 1 to 3 millimeters, with a closer setting used as the kernels mature. However, this can vary according to field, hybrid and growing season, so there's no "one size fits all." The goal is no unbroken kernels, and more than 1 percent unbroken kernels suggests that roller adjustment may be needed. You shouldn't be able to find more than one unbroken (full-sized) kernel in a quart-sized container of chopped corn. More unbroken kernels in the silage mean more kernels that can pass through the cow's digestive tract. It's poor economics to grow, harvest and ensile corn only to have many of the kernels wind up in the manure.

A recent trial comparing 2 versus 4-millimeter roll clearance found a difference of 84 versus 75 pounds of milk per cow with the same dry matter intake. That's about $2 per cow per day of milk, all due to a simple processor roll spacing adjustment. And there's no mystery about the reason: Starch digestibility was 87 percent in silage processed at 2-millimeter versus 75 percent at 4-millimeter roll clearance.

Processor rolls will wear out, just as sure as the tires on your pickup truck will. Be on the lookout for an increased number of whole kernels, often due to more wear in the center of the rolls. Worn rolls cannot be conditioned; they must be replaced. Forage testing lab results suggest that there's a lot of potential for improvement: A summary of over 1,000 samples of processed corn silage found that 42 percent had poor kernel processing scores.


Shredlage is another form of corn silage processing, one that's just entering the mainstream. The availability of Shredlage units has been limited to only the latest three models of Claas forage harvesters, though the company that makes the shredder is making Loren Cut Shredlage replacement rolls to fit some Krone, New Holland and John Deere 7200 Series choppers. The gap between rolls is 2 to 3 millimeters, similar to "normal" silage processing, but recommended TLC is 26 to 30 millimeters, compared with 19 to 20 millimeters for silage processors. This results in several times as many long particles in the silage, but better kernel breakage.

Impact on dairy cow intake and milk production is based on only a couple of trials, but the results are encouraging. In one University of Wisconsin trial, 75 percent of the starch in Shredlage passed a 4.75-millimeter screen, compared to 60 percent passage for processed corn silage. Packing density in silage bags, which were used for the eight-week lactation trial, was slightly higher for Shredlage. Dry matter intake of corn silage Shredlage was higher, and cows eating this silage (versus processed corn silage) made 2.3 pounds more (100.1 versus 97.8 pounds) of 3.5 percent fat-corrected milk per day, with the difference between Shredlage and processed corn silage increasing as the trial period progressed. Most of the difference in milk production can be attributed to better starch digestibility.

A self-propelled forage harvester equipped with a silage processor unit at Miner Institute.
Photo by Everett Thomas.

Is Shredlage the real deal or just a gimmick? I think it's the former. In a University of Wisconsin research trial, it increased milk production, even with Holsteins making 100 pounds of milk per day. Careful analysis provides a reason for the improved production: better starch digestibility. This means more starch available for milk production and less winding up in the gutter or alley.

Last year, while doing some consulting at Fair Oaks Farms (Fair Oaks, Ind.), I had the opportunity to listen to a presentation by Roger Olson, technical director of Scherer Design Engineering, Inc., which makes the Shredlage unit. Olson is a practical fellow, and he made no claims that weren't backed up by data. We'll soon be learning much more about this process, because while there were fewer than 50 units in the U.S. last year, there will be over 170 in 2013, including a fair number in the Northeast.

Ev Thomas has worked as an agronomist in New York for 45 years, first with Cornell University Cooperative Extension, then with the William H. Miner Agricultural Research Institute in Chazy, N.Y., including managing its 680-acre crop operation. He continues to work part-time for Miner Institute and is now an agronomist at Oak Point Agronomics. He has written our Forages column for 15 years and has been an expert contributor on a number of other topics.