The title says “dry matter,” but I’m going to start with talking about water. Why? Well, because without water, we wouldn’t have dry matter. I mean yes, we would, but you understand what I’m getting at. Dry matter (DM) and water go hand-in-hand because all feeds have some percentage of moisture that needs to be removed prior to analyzing the feed. Some folks may reference “moisture content” instead of DM, but they are simply the inverse of each other. One describes the percent of nutrients left after the water is removed, and one describes the amount of water in a feed. Typically, I hear moisture content in reference to a standing crop and then DM is used once the crop is turned into a feedstuff.
So now that we have DM and moisture figured out, we need to discuss why removing water is essential for diet formulation. Animals have daily nutrient requirements for carbohydrates, proteins, fats, vitamins, and minerals. Water dilutes whatever it is mixed with, and in this case, the nutrients an animal needs for production. Therefore, looking at nutrient values after water is removed allows us to make the most accurate diet, so we can provide the animal with its necessary nutrients.
Looking at DM nutrient values also allows us to better compare feeds and determine how much needs to be fed to meet requirements. Let’s think about an example using two hypothetical feeds. Let’s look at a dry alfalfa hay and an alfalfa silage. Let’s say that the dry alfalfa hay is 16% crude protein (CP) and the alfalfa silage is 5.7% CP, both as-fed values. Does this mean the dry hay is of better quality than the silage? Not really. When we break this down by dry matter, the alfalfa hay is 89% DM, and the silage is 30% DM. After a couple of calculations, you’ll find the hay is 18% and the silage is 19% CP on a DM basis. Pretty darn similar! This example demonstrates how including water in the analysis can alter the perception of the quality of feed. You would simply need to use a greater volume of silage (as fed) to reach the desired protein concentration of a total mixed ration compared to the hay.
Monitoring DM of feeds over time is just as important as the first sample you took for analysis. Let’s say you are mixing a ration and you need 600 lb of alfalfa silage on a DM basis. This means we need 2,000 lb of the silage straight from the bunker. Two weeks later, you’re further into the bunker and grab another 2,000 lb of alfalfa silage. Only this time, the DM is 35%. This means you’re not mixing 600 lb of silage, you’re mixing 700 lb. It’s only 100 lb, but it increases the protein of the mix by about 1 percentage point, not to mention that fiber content will also increase. Feeding excess nutrients requires more energy from the animal to break down the excess for excretion and increases ration cost.
Given the weight that DM has on feeding, it is important to know how to measure it yourself. The Koster tester and microwave method have been long used, but there is another kitchen gadget that you may find extremely handy. Behold, the ever-popular air fryer. The University of Arkansas has published a protocol to measure dry matter with this small appliance, a safer method than the microwave, and much cheaper than a Koster tester.
In brief, weigh a 100-gram sample of forage (I have used it for hay prior to baling) and place in a wire basket in the air fryer. An additional wire sheet may be needed to on top of the forage to prevent sample loss. Set the temperature to 250˚F and the timer to 30 minutes. After the forage is done, weigh the sample from the air fryer. The final weight will be your dry matter percentage if a 100-gram sample was used. If a sample other than 100 grams was used, divide the final weight by the initial and multiply by 100 for the dry matter percentage.
In summary, dry matter is an essential aspect of both making feed and feeding the feed. Through knowing the DM and nutrient composition of the feed, you will be better able to adjust the ration as necessary to meet requirements for your animals. Happy dairying!
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