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Extension > Agriculture > Dairy Extension > Forages > Determining dry matter content and making adjustments

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Determining dry matter content and making adjustments

Jim Paulson

The basis for feeding and formulating diets for dairy animals is based on knowing an accurate amount for dry matter intake (DMI). This, in turn, is highly dependent on knowing the dry matter (DM) content of each feed and forage in the diet or TMR. The amount of dry matter intake depends on several factors. The first one is size of the animal, not only whether it is a yearling or a mature cow, but the body weight of the animal. The next important factor, if it is a milking cow, is the milk production level. Cows that milk more tend to eat more. Other factors of lesser impact might be season of the year, but temperature and humidity as well as wind speed can make a difference. Forage type and moisture as well as fermentation quality, molds, heating and other palatability issues also affect DMI.

Determining dry matter content of fresh or ensiled forage is relatively straight forward. It is usually done by determining weight difference after drying for an hour. Using a Koster tester is very common but other methods work as well. It is imperative to know that you have taken all of the moisture out of the sample. First, do not use too big of a sample; a half cup or one fourth of a pound is sufficient. The Koster tester uses its own scale and you need to add 100 grams of wet forage and then dry for an hour. After an hour, you put your sample on the scale again (it should weigh less) and record the weight. Divide the dry weight by the wet weight and multiply by 100 to get the percent dry matter. Subtract that number from 100 to get the percent moisture.

Example 1

You weigh out 100 grams of corn silage. You dry the sample for one hour and find it now weighs 35 grams.

35/100 = .35 x 100 = 35% dry matter or, 100 – 35% = 65% moisture in the corn silage. This would be a good moisture content for good corn silage (ideal moisture is 65-68%).

Example 2

You want to know if your corn silage is ready to chop. You get a fresh chopped sample from a part load you just chopped, weigh out 100 grams and dry it. One hour later, you weigh it and find it now weighs 28 grams. Doing your math, 28/100 = .28 x 100 = 28% dry matter or, 100 – 28 = 72% moisture. We know that this is too wet for chopping and will check again in a couple of days.

Example 3

You are feeding TMR to your milking cows and the last couple of days the cows seem to be eating a lot more and you are feeding about 10% more per day. Has something changed? If no real change in the weather, perhaps you need to check the DM on the silage and haylage. You repeat the procedures above and find the corn silage to be 64% moisture this week while it was 66% last week. Is this the cause for more eating? Probably it is not the case because it is not a really big difference. That could be just a margin of error so you should check the haylage also.

Next, you check the haylage. After drying, you find that the moisture is now 62% but last week it was 49%. That is quite a bit of difference but does it make sense? It does feel wetter and you have been feeding 23 pounds of haylage per cow per day and 50 pounds of corn silage. How much do you change the haylage amount with the new moisture?

23 lb x 51% dry matter = 23 x .51 = 11.73 lb dry of haylage fed last week.

How much should you feed now? The new moisture is 62%. That means that the haylage is 38% DM (100 – 62 = 38). Now, divide the old DM by the new DM:

51/38 = 1.34, which is your multiplying factor for the old amount you were feeding.

1.34 x 23 = 30.82 or 31 pounds per cow per day to feed each cow this week compared to 23 pounds per cow per day last week. In a 100-cow group, that would be 8 pounds difference x 100 or 800 pounds more per day. No wonder they were eating everything fed because you would have been 800 pounds short.

If you think the corn silage is getting a little drier, then make a correction there also.

100 – 64% moisture = 36% DM

100 – 66% moisture = 34% DM last week.

34/36 = .94 multiplying factor. So, take .94 x 50 pounds of corn silage as fed last week and now you should feed .94 x 50 = 47 pounds as fed this week. So, on 100 cows, you should now feed 300 pounds less of corn silage but 800 pounds more of haylage.

This example illustrates why it is important to check moisture on forages weekly. If both forages had changed in moisture, one getting wetter and one getting drier, like this example and in the same amount of change, you might not notice cows eating more or less. But, corn silage and haylage do not substitute equally for each other on a dry matter nutrient basis. You could be compromising the whole ration and cause milk production to go down.

Old dry matter/New dry matter = multiplying factor

Multiplying factor x (old amount fed) = new amount to feed

August 13, 2016

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