Understanding Dry Matter and As-Fed
In animal nutrition, feed is discussed in two primary ways: as-fed and dry matter. Understanding the distinction is the first step to mastering the conversion process. 'As fed' refers to feed in its natural state, including all its moisture content. This is the feed as you would typically weigh and offer it to your animals. Conversely, 'dry matter' refers to the portion of the feed that remains after all water has been removed, representing the true nutrient density. Feeds with high moisture content, like silage or lush pasture, have a significant difference between their as-fed and dry matter weights and nutrient concentrations.
The Importance of Conversion
Accurate conversion is critical for several reasons:
- Comparing Feeds: It allows for a fair comparison of the nutritional content of different feeds, regardless of their moisture levels. For example, comparing the protein percentage of a wet silage to a dry grain is misleading without converting both to a dry matter basis first.
- Balancing Rations: Nutritionists formulate diets based on dry matter intake to ensure animals meet their specific nutrient requirements. Converting these dry matter quantities back to as-fed is necessary for correct feeding management.
- Avoiding Errors: Failing to account for moisture can lead to overfeeding or underfeeding of key nutrients. For instance, feeding a large volume of high-moisture feed might not provide enough actual nutrients, causing energy deficits.
The Dry Matter to As Fed Formula
To convert a nutrient's concentration from a dry matter (DM) basis to an as-fed (AF) basis, you must account for the feed's water content. The formula is straightforward:
% Nutrient (As-Fed) = % Nutrient (DM) x (% Dry Matter / 100)
Let's break down the components of this formula:
- % Nutrient (DM): The percentage of the specific nutrient (e.g., protein, fat) on a dry matter basis. This value is often found in feed analysis reports or nutrition tables.
- % Dry Matter: The percentage of the feed that is not water. To calculate this, subtract the moisture percentage from 100.
Step-by-Step Calculation Guide
To illustrate the process, consider a feed with the following characteristics:
- Nutrient (e.g., Crude Protein) on a DM Basis: 25%
- Moisture Content: 60%
Step 1: Determine the Dry Matter Percentage.
- Dry Matter % = 100% - Moisture %
- Dry Matter % = 100% - 60% = 40%
Step 2: Apply the Conversion Formula.
- % Crude Protein (As-Fed) = 25% * (40% / 100)
- % Crude Protein (As-Fed) = 25 * 0.40 = 10%
This calculation shows that a feed with 25% protein on a dry matter basis has only 10% protein on an as-fed basis due to its high moisture content.
Converting Feed Weight
In addition to nutrient percentages, it is often necessary to convert feed weight. To find the as-fed weight needed to meet a specific dry matter requirement, the formula is also simple:
As-Fed Weight = Dry Matter Weight / (% Dry Matter / 100)
Example: You need to feed an animal 5 kg of dry matter from a feed that is 40% dry matter.
- As-Fed Weight = 5 kg / (40% / 100)
- As-Fed Weight = 5 kg / 0.40 = 12.5 kg
This means you must provide 12.5 kg of the as-fed feed to deliver 5 kg of actual dry matter.
Comparison Table: As-Fed vs. Dry Matter
To clarify the differences, the following table compares key aspects of the as-fed and dry matter bases:
| Feature | As-Fed Basis | Dry Matter Basis |
|---|---|---|
| Definition | Includes all moisture content. | Excludes all moisture content. |
| Nutrient Concentration | Lower percentage due to water dilution. | Higher percentage as nutrients are concentrated. |
| Weight | Higher weight for the same amount of nutrients. | Lower weight for the same amount of nutrients. |
| Use Case | Day-to-day feeding and weighing. | Ration formulation and nutritional comparisons. |
| Example | 100 lbs of silage fed. | 35 lbs of dry matter consumed (if silage is 35% DM). |
Practical Application in Feeding
- Forage Analysis: When evaluating lab results for forages like haylage or baleage, nutrient levels are often reported on a dry matter basis. You must first convert these to an as-fed basis to accurately calculate how much to feed.
- Pet Food Labels: Pet food companies often report nutrient guarantees on an 'as-fed' basis. This can be misleading when comparing wet versus dry foods. Converting all nutrient percentages to a dry matter basis allows for a true comparison of nutritional value.
- Mixed Rations: When combining different ingredients with varying moisture levels into a single diet, all components should be formulated on a dry matter basis first. After the dry matter ration is balanced, you can then convert the required amounts of each ingredient back to an as-fed weight for mixing.
- Seasonal Changes: Pay close attention to environmental changes that affect moisture content, such as new hay that is baled wetter or lush, fresh grass in the spring. Regularly testing and adjusting your dry matter conversions is vital to maintain consistent nutrition for your animals.
Conclusion
Mastering the conversion between dry matter and as-fed is an indispensable skill for precision feeding and ration formulation. By using the dry matter to as fed formula, you can move beyond potentially misleading label information and understand the true nutritional value of your feedstuffs. This ability allows for more accurate ration balancing, helps avoid common nutritional pitfalls, and ultimately contributes to healthier, more productive animals. Whether working with livestock or pets, a solid grasp of these conversions ensures that the animals receive the proper amounts of nutrients they need, regardless of the feed's moisture content. Regular feed analysis and consistent conversion practices are key to unlocking optimal animal performance.
