Dairy cow rations are based on the amount of dry matter, the resulting feed when water is removed, that can be fed to cows to maintain health and achieve high production.

Therefore, to properly balance rations it’s essential to know the dry matter levels of feeds that make up the ration. Forages are the most susceptible to dry matter changes, and dry matter levels should be measured on a regular basis to ensure ration consistency. Dry matter should be measured at least once a week, while larger dairies should consider measuring forage dry matter daily.

Measuring dry matter takes very little time, but yields essential information to properly balance rations. If the dry matter changes and ration adjustments aren’t made, cows could receive less feed than they need to perform to their potential. Small changes in ration dry matter can also disrupt eating habits, sometimes resulting in cows going off feed or being more susceptible to health problems like rumen acidosis. We have provided tips for each step in the process of testing dry matter on the farm so you can easily complete the task while avoiding common mistakes.

Taking the sample
• Representative of the whole crop. Make sure the sample you take is a good representation of the forage you’re currently feeding in the ration. This may mean taking forage from different parts of the storage unit, mixing them together and taking part of the combined forage as the test sample.

• Avoid poor quality. Silage being tested should be free of molds and anything else you wouldn’t feed to the herd.

• The right amount. Using a 100-gram sample provides the necessary amount of forage to accurately test dry matter, plus it makes it easier to calculate a dry matter percentage when you are finished.

Measuring dry matter
• Weigh it. If you are using a plate or bag to hold the sample, make sure you weigh the feed and container separately. You’ll need these weights to complete the dry matter calculation.

• Spread on plate. Once the sample is weighed, place it on a paper plate or in a microwave-safe container. Spread the sample evenly.

• Include water. Place a cup of water in the microwave to prevent overheating the sample. This will prevent overdrying the sample when the moisture is removed.

• Drydown. Wet feeds, like corn silage, should be dried on the highest setting for four minutes. Drier feeds, like hay, should be dried on the highest setting for three minutes.

• Record weights. After the initial drying, record the sample weight. Stir the sample and place in the microwave for another minute on medium power.

• Keep drying. Continue to dry and record sample weights in one-minute increments until there is no weight change from one minute to the next. This will be the sign that the sample is completely dried. If needed, go to 30-second intervals to avoid overheating the sample.

Calculating dry matter
Now you have the two numbers you need to calculate dry matter – the original weight and the dry weight. The formula to calculate dry matter is:

% Dry Matter = 100 – [(original weight – dry weight)/original weight] x 100

Here’s an example of how to calculate dry matter:
• Original weight: 3.5 ounces (100 grams)
• Dried-down weight: 1.2 ounces (34 grams)
• Plug into the formula: 1-[(3.5-1.2)/3.5] x 100 = 34 percent dry matter

Common mistakes
Here are some mistakes that are made all too often when computing dry matters on the farm. Avoid these pitfalls to get an accurate feed dry matter for your ration:

• Some sample is lost during drying. Make sure the sample stays together to avoid inaccurate weights before and after drying.

• Samples aren’t stirred. When large samples are not stirred, parts of the forage sample may be dried while others are not. Stirring ensures the whole sample is dried appropriately.

• Container weights included. Remember if you’re weighing the sample in a container, you must subtract the weight before calculating dry matter.

• Not dried or dried too long. You walk a fine line between a sample being too wet or too dry. Make sure the sample is completely dried before calculating dry matter content. On the other hand, don’t leave the forage sample in the microwave too long. This will cause the sample to burn and result in inaccurate values. If it smells like the sample has burned, get a new sample and start the process over.

• No water cup. The water cup in the microwave during heating provides the moisture needed to make sure the sample doesn’t burn.

• Zero the scale or subtract the container. Regardless of which method you use, remember to include only the sample weight in your calculations.

Measuring dry matter is an easy on-farm tool that, when used properly, can ensure ration consistency from day to day. Accurately measuring dry matter will enable the right adjustments to be made to the ration, which can result in optimal intake, health and production. Take a little time every day to ensure you’re offering your herd the right nutrients by testing forage dry matter levels. EL

Elliot Block
Nutritionist/Researcher
ARM & HAMMER
Animal Nutrition
elliot.block@churchdwight.com

This article topic also appears in Progressive Dairyman. This article has been written specifically for dairy employees. The article in Progressive Dairyman is written for dairy owners and herdsmen.

El Lechero recommends dairy teams read the articles and then discuss how to apply these principles on their own dairies.