Determining Forage Dry Matter

Understanding dry matter is a key concept in animal nutrition. Learn the importance of dry matter and how to measure it using a microwave or Koster tester.
Determining Forage Dry Matter - Videos


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- [Coleen] Hi, I'm Coleen Jones, a research associate in the Department of Animal Science at Penn State.

In this video, you'll learn the importance of testing forage dry matter and Dr. Jud Heinrichs will demonstrate two different methods to estimate dry matter.

Dry matter is very simply what's left after all the water has been removed from a sample, and it's the dry matter that contains all of a feed's nutrients.

You might hear both dry matter and moisture content in various recommendations.

It's easy to convert from one to the other since on a percentage basis, the dry matter plus the moisture equals 100%.

Forage dry matter plays a very important role in animal nutrition, from harvest, to storage, to feeding.

At harvest time, the right moisture content is essential for getting the maximum yield of nutrients and producing palatable forage.

The proper moisture level ensures that silage can be packed well and fermentation can begin.

Too much moisture can result in seepage which is lost nutrients and can allow for fermentation to go too far, resulting in spoilage.

As shown in this table, the right moisture level depends on both the crop and the type of storage.

For dry hay, too much moisture results in heating and mold growth that reduce the nutritive value and palatability of the hay.

Again, the target dry matter depends somewhat on how the hay is being stored.

Dry matter is also important because rations are formulated on a dry matter basis.

This allows us to compare the nutrient content of different feeds on a level playing field.

Changes in dry matter can greatly influence the amount of forage needed to provide specific nutrients in the diet.

Unfortunately, silage dry matter changes frequently.

Testing silage dry matter regularly and adjusting the ration accordingly is a good way to improve the consistency of the diet cows are fed.

This graph shows an example of weekly changes in corn silage dry matter over a four-month period.

Changes in forage dry matter can be due to differences in the forages it was harvested or to weather conditions that increase drying or add water from rain or snow.

This variability creates a problem because rations are formulated on a dry matter basis, but they are mixed and fed on an as-fed or wet basis.

Let's look at an example of how changes in forage dry matter can influence what cows are fed.

In this example, a ration calls for 50 pounds of corn silage on an as fed basis.

When the ration was formulated, the silage dry matter was 36.1%.

Crude protein was 6.2%, and net energy for lactation was 0.8 megacals per pound.

Crude protein and net energy are less variable than moisture, so in this example, we will assume they do not change.

To balance the ration, 18 pounds of corn silage were required.

At 36.1% dry matter, this translates to 50 pounds of as fed corn silage.

You can see here that if the dry matter changes but we keep feeding 50 pounds of silage, we either over or underfeed corn silage, which means protein and energy are affected as well.

Failure to adjust feeding amounts as forage dry matter changes can negatively affect cows' milk production and energy balance.

On the other hand, overfeeding forages results in wasted feed, excess nutrients, and increased excretion of nutrients in manure.

We recommend testing forage dry matter before and during harvest to ensure proper fermentation and maximize the nutritional value of the silage.

During feed out, test forage dry matter two times per week.

There are several options for testing dry matter on the farm, and we will demonstrate two methods beginning with the microwave.

The microwave is used to dry a sample and the moisture content is calculated using the change in the sample weight before and after drying.

Now, Dr. Jud Heinrichs will walk you through the steps of using a microwave for forage dry matters.

- What I'm gonna show you today is how to do a microwave dry matter on a forage.

It's a relatively simple thing to do on farm and gives you a good, accurate value on dry matter.

Start off with I'm gonna use a paper boat in this case or paper plate, don't use styrofoam cause it'll burn.

I'm gonna tear this and then put about 50 grams of a forage sample in this.

Record your weight.

And put it in the microwave.

Gonna use a standard microwave at full power setting.

Okay, this is corn silage that's less than 40% dry matter so I'm gonna start off with a minute and a half time.

(microwave beeps)

And you take this out of the oven, you wanna move it around a little, make sure you don't develop any hot spots in it.

You're gonna record the weight, in this case it's not anywhere near dried yet, so I'm gonna have to write it down, gonna put it back in next time for about 35 to 40 seconds.

You put it each subsequent time it's gonna go back in for a shorter time period.

When your sample is about dry, you're gonna take it out, pretty obviously getting quite dry, take a weight on this sample, either record it or remember it for now, and then put it back in for very short intervals like 10 second intervals to make sure that it's finally dry at the end.

When it's the same weight two times in a row and you don't have to have it cool down, it can be still hot, you get the same weight two times in a row, you record that amount, and that's gonna give you your dry matter basis and then you do the calculation based on what you started with in the sample.

One final point is don't put a glass of water in the microwave, it's gonna be impossible to get it down to zero percent moisture when you're running water in there.

- [Coleen] As a review, this table shows suggested times for drying samples in the microwave.

Depending on the forage, your first drying time will be about a minute to a minute and a half.

With each subsequent drying period getting progressively shorter until the sample weight stops changing.

Another popular method for determining dry matter is the Koster Tester.

In this method, we dry the sample and calculate the moisture content by the difference between the starting and ending weight of the sample.

Here's Dr. Heinrichs again to demonstrate the Koster method.

- This is another system for analyzing dry matter on a farm called Koster Tester.

What I do in this case is again I take a paper plate, I'm gonna put about 50 grams of sample on here.

Record the weight, and then I'm gonna put it in the Koster Tester, spread it out to make sure it's evenly spread over the screen, let it go for 30 minutes and come back, take the weight, pour it back in your pan, record the weight, and then I'm gonna put it back in for 10 minute intervals, again record the weight after 10 minutes and when you have two weights in a row that are the same, then you got your sample dry and you go through the calculation of dry matter.

- [Coleen] These methods produce accurate results when compared to samples tested for forage dry matter using forced air drying in a lab.

However, the Koster Tester tends to underestimate dry matter compared to the microwave method.

This may be due to smaller particles being blown out of the tester or to incomplete drying of corn kernels.

Although we haven't shown them here, there are electronic testers that use a probe to estimate dry matter by measuring electrical conductivity of the forage.

These testers can take several readings over a short period of time but tend to be more variable and less accurate than the other methods.

Another more recent method of testing forage dry matter is the handheld moisture tester that uses NIR technology to estimate dry matter.

Multiple measurements can be made quickly and stored on a USB drive for later download.

This is a relatively new technology and the calibration equations are continually being refined and expanded to include additional feeds.

Although this option is expensive, it provides the fastest results of any method and could easily be used daily to adjust diets for changes in dry matter.

Regardless of the method you use, remember that monitoring forage dry matter is one of the easiest steps you can take to harvest crops at the right time and to ensure your cows are fed a consistent diet every day.


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