Extending Livestock Feed Supplies:
Glossary of Terms Used in Livestock Nutrition
As Fed
Refers to the nutrient content of a feed in the form consumed by the animal, including moisture.
Typical dry matter (DM) values:
- Silage: 30–45% DM (as fed)
- Hay: 85–90% DM (as fed)
Conversion:
- % Nutrient (as fed) = (% nutrient on 100% DM basis × % DM) / 100
- Commercial feed tags commonly express nutrient content on an as‑fed basis.
Dry Matter (DM)
Represents the portion of feed remaining after all moisture is removed. Used to accurately compare feeds with different moisture contents.
Conversion:
- % Nutrient in DM = (% nutrient as fed × 100) / % DM
Essential Nutrients
Nutrients that must be supplied to maintain life. The five essential nutrients are:
1. Energy
Provides heat, supports growth, reproduction, lactation, and weight gain.
Common expressions: TDN (Total Digestible Nutrients), DE (Digestible Energy).
Common expressions: TDN (Total Digestible Nutrients), DE (Digestible Energy).
- 1 kg TDN ≈ 4,400 kcal DE.
2. Protein
Critical for growth and tissue development. Proteins are made from amino acids.
- Urea can supply nitrogen for rumen microbes to synthesize microbial protein when included appropriately in rations.
3. Minerals
Represent the “ash” remaining after burning feed.
- Calcium and phosphorus are the two most abundant minerals in the body.
- Mineral supplement labels typically list calcium first and phosphorus second (e.g., 20:10 = 20% Ca : 10% P, or a 2:1 mix).
4. Vitamins
Required in small amounts for normal physiological function.
- Fat‑soluble vitamins: A, D, E, K (can be stored by the body).
- Vitamins A, D, and E must be supplied in the diet.
- Ruminants can synthesize all other essential vitamins.
5. Water
The most essential nutrient for maintaining immediate body health and normal function.
Moisture Content
The percentage of water present in feed. Important for evaluating dry matter intake and nutrient delivery.
Total Digestible Nutrients (TDN)
Estimates the energy content of a feed as the sum of digestible protein, digestible carbohydrates, and digestible fat × 2.25.
- In forages, TDN is largely predicted from fiber content.
- As fiber increases, TDN decreases due to reduced digestibility.
Acid Detergent Fiber (ADF)
· ADF includes cellulose and lignin and is used as an indicator of forage digestibility.
· Higher ADF generally means lower digestibility.
Neutral Detergent Fiber (NDF)
· NDF measures most of the structural components in plant cells (i.e. lignin, hemicellulose and cellulose), but not pectin.
· The level of NDF in the animal ration influences the animal's intake of dry matter and the time of rumination. The concentration of NDF in feeds is negatively correlated with energy concentration.