What is Nitrogen-Free Extract (NFE)?
Nitrogen-Free Extract, or NFE, is a component of animal feed determined through the proximate analysis system. This traditional method categorizes feed into six fractions: moisture, crude protein, crude fat, crude fiber, ash, and NFE. NFE represents the portion remaining after measuring and subtracting the percentages of the other components from 100%.
The Weende Proximate Analysis System
The proximate analysis system, also known as the Weende analysis, divides feed carbohydrates into crude fiber and NFE. NFE includes readily digestible components like simple sugars and complex starches, serving as a primary energy source for many animals. The term "Nitrogen-Free Extract" can be misleading as it's neither a true extract nor a measure of nitrogen.
How NFE Carbs Are Calculated
NFE is a calculated value, not directly measured. This means any errors in measuring other components affect the final NFE percentage.
The NFE Calculation Formula
The formula for NFE (on a dry matter basis) is:
$NFE = 100\% - (\%\,Moisture + \%\,Crude\,Protein + \%\,Crude\,Fat + \%\,Crude\,Fiber + \%\,Ash)$
Each component is determined through specific lab procedures, such as drying for moisture, Kjeldahl for protein, ether extraction for fat, acid and alkali digestion for crude fiber, and incineration for ash.
What Do NFE Carbs Consist Of?
NFE mainly includes non-structural carbohydrates providing energy. This includes sugars (glucose, fructose, sucrose) and starches. It can also contain other soluble substances like some vitamins, pectin, and hemicellulose.
The Importance of NFE in Animal Nutrition
NFE is a long-standing metric, particularly for non-ruminants. It's used in:
- Diet Formulation: Helping nutritionists create balanced diets with adequate energy, often utilizing grains high in starch (a main NFE component).
- Energy Estimation: Contributing to the estimation of total digestible nutrients (TDN) and overall energy content of feed.
- Quality Assessment: A higher NFE can indicate higher energy in some feeds, like cereal grains.
Limitations and Disadvantages of Using NFE
The NFE system has limitations, leading to modern methods like Van Soest detergent fiber analysis.
- Accumulated Errors: Calculation by difference means errors in other measurements compound in the NFE value.
- Inaccuracy for Ruminants: Crude fiber analysis underestimates total fiber, with some indigestible material ending up in the NFE fraction, making it less reliable for ruminants.
- Lack of Specificity: NFE doesn't differentiate between types of sugars and starches, which can be important for specific dietary needs.
NFE vs. Other Carbohydrate Measures
Here's a comparison of NFE with other carbohydrate measures:
| Feature | Nitrogen-Free Extract (NFE) | Crude Fiber (CF) | Detergent Fiber (NDF/ADF) |
|---|---|---|---|
| Measurement Type | Calculated by difference | Measured directly (Weende) | Measured directly (Van Soest) |
| Carbohydrate Type | Soluble (sugars, starch) | Insoluble (cellulose, lignin) | Insoluble (NDF: cellulose, hemicellulose, lignin; ADF: cellulose, lignin) |
| Primary Use Case | Older system, mostly for non-ruminants | Older system, significant inaccuracies | Modern, especially for ruminants, accurate fiber |
| Energy Source | High energy value | Lower energy value | Indicates feed bulk and potential digestibility |
| Accuracy | Prone to error accumulation | Inaccurate, underestimates fiber | More accurate for fiber fractions |
Conclusion
NFE carbs are a historical concept in animal feed analysis, providing a calculated estimate of digestible carbohydrates like sugars and starches. While useful for general feed assessment, particularly for non-ruminants, its limitations, including inaccuracies and lack of specificity, are important to acknowledge compared to modern methods. Advanced fiber analyses are often preferred for precise nutritional management, especially for ruminants. Understanding NFE within feed evaluation aids in making informed dietary decisions.
Learn more about modern feed analysis from the Montana State University Animal Range Handbook.
