Understanding Forage Quality and Feeding Programs
Forage quality directly influences the effectiveness of feeding programs by determining how well the nutrient composition of feed meets animals’ daily nutritional needs. However, forage quality can vary significantly, even within a single harvest, due to environmental conditions and timing. Testing forage quality provides critical information for ensuring animal health and optimizing feed utilization.
Why Test Forage Quality?
Low-quality forages have fewer available nutrients, requiring greater supplementation and potentially predisposing animals to health issues like hepatic lipidosis. Common supplemental feeds, often cereal grain-based, can also pose risks if overconsumed, such as digestive upsets or acidosis.
Practical Forage Testing Methods
Modern forage analysis uses biological, chemical, and near-infrared reflectance (NIR) spectroscopy to determine nutrient content. While wet chemistry remains the “gold standard,” NIR is faster and less expensive, providing accurate results for crude protein and fiber content. Testing forage samples through certified laboratories (available via the National ForageTesting Association) is recommended for reliable data.
Key Forage Tests
- Dry Matter (DM): Indicates moisture content and allows nutrient comparison on a consistent basis.
- Neutral Detergent Fiber (NDF): Measures total cell wall content; higher values correlate with reduced intake and quality.
- Acid Detergent Fiber (ADF): Focuses on indigestible components like cellulose and lignin; higher values indicate lower energy content.
- Crude Protein (CP): Reflects nitrogen content and provides insight into forage maturity and fertilization practices.
| Essential Nutrients | Chemical Components | Analytical Procedures | ||
|---|---|---|---|---|
| Fatty acids, Fat-soluable vitamins | Lipids, pigments, sterols | Ether Extract | ||
| Protein, amino acids | Nitrogen-containing compounds – Protein, Nonprotein nitrogen | Kjeldahl Procedure (Crude Protein) |
||
| Inorganic minerals | Ash | Ashing (complete combustion) | ||
| Carbohydrates | Glucose | Sugars | Nonstructural Carbohydrates** | Nonfiber Carbohydrates+ |
| Starches | ||||
| Dietary Fiber | Soluable Fiber | |||
| Hemicellulose | Neutral Detergent Fiber | |||
| Cellulose | Acid Detergent Fiber | |||
| Lignin* |
*Lignin is not truly a carbohydrate compound but is so intimately associated with cell wall carbohydrates that it is often included as such.
**Newer methods are being used to measure starch content.
+Determined by difference (100 – CP – EE – NDF – Ash).
Source: PennState University Extension
| % Nutrient Content: | ||||||
|---|---|---|---|---|---|---|
| Nutrient Density Basis* | DM | Protein | NDF | ADF | Calcium | |
| Grass Pasture | AF | 20 | 2.2 | 11.0 | 8.0 | 0.12 |
| DM | 100 | 11.0 | 55.0 | 40.0 | 0.60 | |
| Grass Hay | AF | 90 | 9.9 | 49.5 | 36.0 | 0.54 |
| DM | 100 | 11.0 | 55.0 | 40.0 | 0.60 |
*Conversion formula: As Fed nutrient content = DM nutrient content x DM ratio or DM nutrient content = As Fed nutrient content/DM ratio. DM ratio is 0.2 for pasture and 0.9 for hay in this example.
Source: PennState University Extension
Visual Assessment
Forage quality can also be assessed through sensory evaluation, including appearance, texture, and smell. While less precise than laboratory testing, this method provides practical insights, especially for small-scale purchases.
| Testing Method | Description/Comment |
|---|---|
| Sensory Evaluation | |
| Visual | |
| Stage of maturity | Look for the presence of seed heads (grass forages) or flowers or seed pods (legumes), indicating more mature forages |
| Leaf to Stem ratio | Look at forage and determine whether the stems or leaves are more obvious; good-quality legume forages will have a high proportion of leaves, and stems will be less obvious and fine |
| Color | Color is not a good indicator of nutrient content, but bright green color suggests minimal oxidation; yellow hay indicates oxidation and bleaching from sun, and hay will have lower vitamins A and E content |
| Foreign Objects |
Look for presence and amount of inanimate objects (twine, wire, cans, etc.), weeds, mold, or poisonous plants |
| Touch | Feel stiffness or coarseness of leaves and stems; see if alfalfa stems wrap around your finger without breaking; good-quality hay will feel soft and have fine, pliable stems |
| Smell | Good quality hay will have a fresh mowed grass odor; no musty or moldy odors |
| Chemical Testing | |
| Moisture/Dry Matter | Measures amount of moisture in forage; moisture content will determine how well the forage will store without molding; Goal for any hay <15% moisture (>85% dry matter) |
| Neutral Detergent Fiber | Measures total cell wall content of plant and indicates maturity; the higher the value, the more mature and lower quality the forage; Goal < 40% Alfalfa and < 55% Grasses |
| Acid Detergent Fiber | Measures the more indigestible portion of cell wall and reflects degree of lignification; Higher values indicate more mature, lower quality forages; Goal: < 35% Alfalfa and < 35% Grasses |
| Crude Protein | Crude protein content reflects maturity of forage as well as fertilization amount; Good-quality forages generally will have higher protein content; Goal > 9% Grasses and >15% Alfalfa |
Source: PennState University Extension
