Understanding the Basics: As-Fed vs. Dry Matter
To effectively manage livestock nutrition, it is crucial to understand the difference between 'as-fed' and 'dry matter' (DM). The as-fed basis refers to the feed's nutritional composition, including its natural water content, as it is presented to the animal. This can be misleading because the moisture content varies dramatically between feed types—from a high percentage in fresh forage or silage to a low percentage in dry hay or grains. All the actual nutrients, such as protein, fats, and minerals, are contained within the feed's dry matter portion.
Converting all feeds to a common dry matter basis standardizes comparisons by eliminating the variable water content. This is particularly important when formulating mixed rations with ingredients of different moisture levels, as it ensures the animal receives the intended balance of nutrients. Without this conversion, you might over or under-feed critical nutrients, impacting animal growth, milk production, and overall health.
Step-by-Step Guide to Converting As-Fed to Dry Matter
Converting a nutrient value from an as-fed basis to a dry matter basis is a straightforward process requiring two key pieces of information: the nutrient's as-fed percentage and the feed's moisture content. The dry matter percentage is simply 100% minus the moisture percentage.
The Conversion Formula
The core formula for this conversion is:
$$ \text{% Nutrient (Dry Matter Basis)} = \frac{\text{% Nutrient (As-Fed Basis)}}{\text{% Dry Matter}} \times 100 $$
Practical Example: Converting As-Fed Nutrient Percentage
Let's apply this formula to a real-world scenario. Imagine you have a sample of wet feed, like silage, with the following analysis:
- Moisture: 60%
- Crude Protein (As-Fed): 10%
Here is how you would convert the crude protein to a dry matter basis:
-
Calculate the Dry Matter Percentage:
Dry Matter %=100%-60%=40%
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Divide the As-Fed Nutrient Percentage by the Dry Matter Percentage (as a decimal):
10%/0.40=25%
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The Result:
- The crude protein content is 25% on a dry matter basis. This higher, more concentrated number reflects the nutrient density once all the water is removed.
Converting Feed Amounts
In addition to nutrient values, you can also convert the weight of feed to a dry matter basis. This helps determine the actual amount of nutrients an animal is consuming, especially when intake is measured on an as-fed basis.
$$ \text{Amount (Dry Matter Basis)} = \text{Amount (As-Fed Basis)} \times \frac{\text{% Dry Matter}}{100} $$
For example, if an animal eats 40 lbs of a feed that is 60% dry matter, the dry matter intake would be:
40 lbsx0.60=24 lbsdry matter.
Comparison: As-Fed vs. Dry Matter Analysis
| Feature | As-Fed Basis | Dry Matter Basis |
|---|---|---|
| Inclusion of Water | Includes all moisture content. | Excludes all moisture content (100% water removed). |
| Nutrient Concentration | Apparent nutrient concentrations are lower due to dilution by water. | All nutrient percentages are higher, showing true concentration. |
| Comparison Value | Unreliable for comparing feeds with different moisture levels. | The standard and most accurate method for comparing different feeds. |
| Primary Use | Reporting nutrient guarantees on feed labels. | Ration formulation, balanced feeding, and scientific analysis. |
| Example Feed | Lush pasture (low DM), silage (medium DM), or fresh vegetables. | Dehydrated alfalfa pellets, dry grains, or mineral supplements. |
Conclusion: The Importance of Dry Matter Conversion
Understanding how to convert as-fed to dry matter is an indispensable skill for anyone involved in animal feeding and nutrition. It provides a consistent, standardized, and accurate metric for evaluating nutrient density, formulating rations, and ensuring animals receive a balanced diet. By removing the variable of water from the equation, you can make more informed decisions, optimize feed efficiency, and ultimately improve the health and productivity of your livestock. Regular monitoring and adjustment based on dry matter content are key to maximizing profitability and minimizing waste in any feeding program. For those working with farm animals, resources from university extensions and the USDA provide excellent guidance and tables for common feed types.
