Feeding Value and Nutritive Value of Feeds

  • Feeding Value (FV)

    • Definition: Feeding value encompasses both the nutritive value (NV) of a feed and the ability of the animal to consume it.

    • Formula: FV = NV x intake

    • Important: Knowing the animal's nutrient requirements (Metabolizable Energy - ME and Metabolizable Protein - MP) is essential, but the animal's response to feed varies based on feeding value.

  • Nutritive Value (NV)

    • Definition: NV measures a food's ability to support metabolic activities in an animal's body, distinguishing it from physical or chemical measurements. (Blaxter 1956)

    • Variation: NV differs depending on the physiological status of the animal (e.g., lactating vs. growing animals).

    • Prediction: NV is generally predicted using the feed's chemical composition, though no single method offers complete accuracy.

  • Importance of Feed Composition

    • Measurement of components can inform on availability and nutrient content. Understanding the specific nutrient profiles helps in formulating diets that meet the distinct needs of different animal categories.

  • Components of Forages:

    • Types: Grasses, legumes, brassicas, grains, and weeds.

    • Cell Types: Include parenchyma, mesophyll, vascular bundles, etc.

    • Chemical Components: Protein, organic acids, sugars, fibers, etc.

    • Toxins: Endophytes, fungi, alkaloids, and other contaminants.

  • Interpreting Feed Composition

    • Laboratory analysis provides chemical composition data, aiding in management decisions regarding feed.

    • Forages often show greater variability in composition than formulated feeds (e.g., grains and supplements).

  • Influence of Management on Forage Quality

    • Factors such as grazing intervals and sowing dates significantly impact forage maturity and characteristics.

    • Different plant species and parts possess various nutrient contents affecting overall NV.

  • Digestibility

    • Digestibility serves as a key indicator of NV, reflecting how well nutrients are absorbed and utilized.

    • Factors: Composition, fiber content (negatively correlates with digestibility), diet composition, and feed preparation can all affect digestibility.

    • Formula to calculate apparent digestibility:

    • Apparent digestibility=nutrient consumed−nutrient in dungnutrient consumed\text{Apparent digestibility} = \frac{\text{nutrient consumed} - \text{nutrient in dung}}{\text{nutrient consumed}}

    • Example Calculations:

    • Ryegrass with 16 kg DM/d consumed and 3.3 kg DM/d dung:

      • Apparent digestibility=(16−3.3)16=0.794 or 79.4%\text{Apparent digestibility} = \frac{(16 - 3.3)}{16} = 0.794 \text{ or } 79.4\%

    • Plantain calculation details provided.

  • Conclusion on Nutritive Value

    • Digestibility is the primary measure of NV.

    • Management strategies that increase fiber (like lignin and cellulose) may adversely impact NV and FV, leading to lower digestibility.