Understanding Dry Matter and Feed Rations

What Is Dry Matter?

Every feed your livestock eats contains two things: water and dry matter. Dry matter (DM) is everything left after you remove all the moisture — the proteins, carbohydrates, fats, fiber, minerals, and vitamins that actually nourish your animals. Understanding this distinction is the single most important concept in practical feed management.

Different feeds contain dramatically different amounts of water. Corn silage is typically about 35% dry matter and 65% water. Alfalfa hay runs around 88-90% dry matter with only 10-12% water. Corn grain is similar to hay at about 88% dry matter. Fresh pasture can be as low as 20-25% dry matter depending on conditions.

This means that when you feed 10 kg of corn silage, your animal is really only getting 3.5 kg of actual feed material. The other 6.5 kg is water. But when you feed 10 kg of alfalfa hay, the animal gets 9.0 kg of actual feed. Equal weights on the scale, very different amounts of nutrition.

Why Dry Matter Basis Matters

If you compare feeds on an "as-fed" basis (the weight as it comes off the scale), you are including all that water in the comparison. This makes high-moisture feeds look equivalent to dry feeds when they are not. A ration of 20 kg as-fed that is half silage and half hay actually contains only 12.5 kg of dry matter, not 20 kg. The missing 7.5 kg is water that contributes nothing nutritionally.

Expressing feeds on a dry matter basis creates an apples-to-apples comparison. When a feed analysis reports crude protein at 20% on a DM basis, it means that 20% of the actual feed material (not counting water) is protein. This lets you fairly compare hay protein to silage protein, grain to supplement, regardless of how much water each contains.

This is why nutritionists always work on a DM basis when formulating rations. The animal's nutrient requirements are stated in terms of dry matter intake, and every feed ingredient's nutrient content is evaluated on a dry matter basis. If you skip this step, your ration may look balanced on paper but actually deliver too little protein, energy, or fiber.

Reading a Feed Test Report

A forage analysis report from a testing laboratory is the most accurate way to know what your feed actually contains. Book values (like those in NRC tables) are useful averages, but your specific hay field or silage pit may differ significantly based on harvest timing, growing conditions, and storage.

The key values to look for on your report are:

• Dry Matter (DM%): The percentage of the sample that is not water. This is the foundation for all other nutrient calculations. If your silage tests at 32% DM instead of the book value of 35%, your ration math will be off unless you use the tested value.
• Crude Protein (CP%): Total nitrogen content multiplied by 6.25, expressed on a DM basis. This includes both true protein and non-protein nitrogen. Beef cattle at maintenance need about 7-8% CP in the total ration; lactating dairy cows need 16-18%.
• Total Digestible Nutrients (TDN%): A measure of feed energy on a DM basis. TDN represents the sum of digestible protein, fiber, nitrogen-free extract, and fat (multiplied by 2.25). Higher TDN means more energy available. Grains typically test 80-88% TDN, while mature grass hay may only be 50-55%.
• Neutral Detergent Fiber (NDF%): The total cell wall content including cellulose, hemicellulose, and lignin. NDF is the best predictor of voluntary intake — higher NDF means the animal feels full sooner and eats less. Forages range from 40% (alfalfa) to 68% (bermudagrass hay), while grains are much lower at 9-18%.

Always check whether the report values are on an "as-received" (as-fed) or "dry matter" basis. Most labs report both. Use the DM basis values for ration formulation, and the as-fed values for calculating how much physical feed to deliver.

Building a Basic Ration

A livestock ration is simply the combination of feeds an animal receives each day. Building a ration starts with understanding three things: what the animal needs (nutrient requirements), what your available feeds provide (nutrient content), and how much the animal can eat (dry matter intake capacity).

The general approach for ruminants (cattle, sheep, goats) is:

1. Start with forage. Forages (hay, silage, pasture) should make up at least 40-60% of the ration dry matter for ruminants. They provide the fiber needed for proper rumen function. Choose the best quality forage you have available.
2. Add energy. If the forage alone does not meet energy requirements (TDN is too low), add a grain source like corn, barley, or wheat. Grains are high in TDN but low in fiber, so they boost energy without filling the animal up.
3. Add protein if needed. If the total ration CP is below the animal's requirement, add a protein supplement like soybean meal, cottonseed meal, or canola meal. These are concentrated protein sources that are fed in smaller quantities.
4. Check the totals. Add up the DM quantities and nutrient contributions from all ingredients. Calculate the weighted average CP%, TDN%, and NDF% on a DM basis. Compare these to the animal's requirements.

The feed ration builder calculator automates step 4 for you. Enter your ingredients and quantities, and it shows the DM conversion and weighted nutrient totals instantly. This makes it easy to see how changing one ingredient affects the whole ration.

Common Mistakes

• Comparing feeds on an as-fed basis. This is the most common error. Saying "I feed 50% silage and 50% hay" by weight sounds balanced, but on a DM basis the hay contributes far more nutrition. Always convert to DM before evaluating ration balance.
• Ignoring moisture changes in silage. Silage DM content can vary from 30% to 40% depending on the location in the pile and how long it has been open. Test silage DM regularly and adjust feeding amounts when moisture changes.
• Over-supplementing protein. Protein supplements are expensive. If your forage already provides enough CP for the animal's production level, adding more protein wastes money. The excess nitrogen is excreted as urea, costing you feed dollars with no production benefit.
• Using book values instead of tested values. NRC book values are useful starting points, but your specific feeds will differ. A feed test costs $15-30 per sample and can save hundreds in wasted supplement or lost production. Test at least your primary forages each year.
• Forgetting about NDF and fill. An animal can only eat a certain amount of DM per day, and NDF is the main limiter. If your forage NDF is very high (above 60%), the animal physically cannot eat enough to meet energy needs, no matter how much you put in front of it. In this case, adding some lower-NDF feed (grain or good alfalfa) increases total intake.