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0807 PD: Wide swathing of forages: What do we know?

L.E. Chase Published on 02 August 2007

Forage quality is one of the key driving factors that determine milk production, rumen health and profitability on dairy farms. The benefits of high-quality, highly digestible forages for use in dairy cattle rations is widely accepted by both dairy producers and the nutrition advisors that work with them.

There is no lack of knowledge of the factors and principles that need to be followed to grow, harvest, store and feed high-quality forages. Seed companies continue to improve the plant genetics available. Equipment companies have made great improvements in machinery for harvesting forage.

Dairy producers have invested in storage facilities and have stepped up their intensity and efforts to produce high-quality forage.

Forage testing labs have increased the analytical information provided on forages. Nutrition advisers are using ration formulation programs that utilize the additional information provided by forage testing labs to develop rations. Even though overall forage quality continues to improve, there is still too much variability in quantity and quality that occurs both within and between years.

The total dry matter (DM) losses from cutting through feeding are typically in the range of 20 to 30 percent of the original standing crop. In addition, there can be significant decreases in forage quality that occur in the harvest and storage process.

A major reason for this variation is the weather patterns and conditions that occur at forage harvest time. In the Northeast and Midwest areas of the United States, this is a significant challenge for harvesting first-cutting alfalfa and grass forages.

Forage standing in the field is usually less than 20 percent DM prior to cutting. Depending on the forage storage system in use on the farm, the desired forage DM content at harvest ranges from 30 to almost 90 percent DM. To achieve these changes in forage DM content may require two to four days of field drying. How many times in late May and early June do we have two to three days without rain?

One way to decrease the risk of weather damage to the quality of the forage harvested is to find ways to increase the rate of drying after the forage is cut. A number of approaches have been used to do this. One approach was the use of chemical drying agents. A second approach is laying the forage out in wider swaths that increase the surface area exposed to the sun and air. The main goal in harvesting and storing forages is to preserve as much of the quality and quantity of the crop at the time of cutting.

Forage drying rate

What controls the rate at which moisture is removed from forage during the field drying process? The primary factors that control the rate of field drying are:

–swath surface exposed to sun

–amount of sun

–swath temperature

–vapor deficit

–crop moisture

–wind velocity

•factors that decrease drying rate:

–high humidity

–swath density

–soil moisture

The basic principle is to obtain a wide, thin layer of material exposed to the sun to enhance drying rate and reduce field drying time. In some cases, second- and third-cutting forages put into wide swaths may reach the desired DM content for silage harvest within two to four hours after mowing.

How do plants lose moisture?

There are basically three different phases involved in the field drying process that occurs in forages. These are:

•Phase 1 – This is the early phase initiated when the crop is cut. Moisture moves along the length of the stem and through the leaf. It appears that at least 35 percent of the moisture in alfalfa stems is lost through the leaves.

The main method of moisture loss through the leaves is via the stomata, the primary mechanism of moisture leaving growing plants. The stomata are the pores in the leaf through which carbon dioxide and oxygen can move and moisture can leave the plant. The stomata are only effective as a means of water movement when they are open. Light, temperature and water content are primary factors to stimulate the stomata. Usually, they are open during the day and close at night.

Stomata usually close when the plant DM content is 35 to 43 percent. Research in New York has indicated wide swaths receive about three to four times as much sunlight as narrow swaths. Mechanical crushing or conditioning of the stem may disrupt the capillary flow of moisture from the stem to the leaves.

At the end of Phase 1, forages should be at the proper DM content for silage harvest.

•Phase 2 – The main method of moisture movement in this phase is movement of water from the core of the stem to the stem surface. Water movement via the length of the stem is minimal in this phase. Mechanical conditioning can be helpful during this time as it disrupts the epidermis on the plant stem.

•Phase 3 – This occurs when plants are greater than 55 percent DM and results in the removal of the tightly held water.

What about using conditioners at harvest?

There is some disagreement on this question. The answer may depend partly on whether the forage is harvested for storage as silage or hay. There may also be differences in the type of conditioner used and the extent of conditioning applied to the crop.

New York workers question the value of conditioning forages that will be harvested as silage. These workers were laying swaths out at 90 percent or more of the cut width. Wisconsin workers compared conditioned and unconditioned alfalfa swaths for drying rates. Windrows were 33 percent of the cut width and swaths were 65 percent of cut width.

Tedding was also done immediately after cutting to get a swath that was 100 percent of the cut width. These results indicated conditioning and drying in a swath dried about as fast as unconditioned alfalfa laid out to the full cutting width. The authors indicate the unconditioned swaths need to be about twice as wide as the conditioned swaths to result in a drying advantage for not conditioning.

One problem is that current equipment will only produce swaths up to about 85 percent of the cut width. The average for a number of machines currently available was a swath width of about 65 percent of cut width.

What changes occur in forage composition?

The plant continues to undergo respiration and protein degradation (proteolysis) for a period of time after cutting. During this time, plant true proteins are converted to nonprotein nitrogen (NPN) compounds. There is also a decrease in the sugar and starch content as these carbohydrates are used as energy sources during respiration. The following changes in forage composition have been reported to occur during the wilting process:

•The NPN content of the forage increases by 20 to 50 percent

•Sugar content can be reduced by 5 to 20 percent

•Starch content can be reduced by up to 40 percent

The end result is that the net energy content of the wilted material is lower than the energy content of the original material. Kilcer used the Milk 2000 program and estimated wide swath forages had the potential to produce 300 pounds more milk per ton of DM than forages wilted in narrow swaths.

Some caution is needed in interpreting this value. Logic would indicate forage that takes less time to wilt to the desired DM level would have less proteolysis and respiration and should have a higher nutritive value. This forage should also have an opportunity for better silage fermentation since it would be higher in sugar content. However, information to confirm a better fermentation from wide swath silages is not available. Currently, there are no animal trials that have been conducted to compare forages wilted in narrow versus wide swaths.

What are the challenges?

Wide swathing of forages appears to offer opportunities to harvest forages with less weather risk and a resulting higher nutritive value product. A number of dairy producers have adopted this system and are pleased with the results. However, there are some challenges producers face when considering adopting this management system. These include:


Currently available mowers will not lay out wide swath windrows (greater than 90 percent of the cut width). Thus, tedding may be needed to produce a wide swath. There are a number of companies designing equipment to produce wide swaths.

•Organizing equipment and labor

Wide swathing lets forage dry faster and decreases the time interval between cutting and chopping. With the new high-capacity harvesters on farms, there will not be enough forage to harvest unless extra mowing capacity is added. This adds both equipment and labor cost.


A method is needed to merge the wide swaths into windrows for the harvester. This is an added investment in equipment that may be needed to implement this system. Additional labor may be needed to operate this equipment since mowing and forage harvesting could also be taking place at the same time other forage is being merged.

•Research data

Additional controlled research data is needed to permit a better economic evaluation of the potential costs and returns of a wide swath system. Data is also needed on potential changes in fermentation quality. If the wide swath forage has higher soluble carbohydrate levels, will a more efficient fermentation take place?

•Animal data

Currently, only forage analytical data is available for evaluation purposes. With the current ration models available to the industry, projections can be made of anticipated animal response. Will dairy producers accept this information as part of their decision-making process? Will actual animal performance trials be required?

•Forage harvest risk

The wide swath approach should result in higher forage quality being harvested since the weather risk is reduced. What is the value of a higher crude protein (CP) and lower neutral detergent fiber (NDF) forage to the overall farm operation? Will wide swathing assist in consistently obtaining an additional cutting of forage?


The wide swath approach makes biological sense in terms of reducing the weather risk of forage harvest and producing higher nutritive value forage. The data currently available is encouraging and fits with biological logic. The availability of equipment to implement this system is still a concern. There are also some logistical and labor organization issues that need to be considered before this system is adopted on a farm.

A number of dairy producers have implemented this system and seem pleased with the results to date. Other producers are still questioning the additional costs (labor, equipment) needed to implement this system with the limited data currently available.

Anything that can be done to lower the weather risk for forage harvesting should improve overall forage quality on the farm. Wide swathing of forages is one practice that has the ability to decrease the risk of weather on forage harvesting.  PD

References omitted but are available upon request at

—From 2006 Vita Plus Dairy Summit Proceedings

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