Understanding the Basics of Feed Composition
Before you can begin calculating, it is essential to understand what makes up a feed's composition. A balanced feed ration must provide all the nutrients an animal needs, including carbohydrates, proteins, fats, vitamins, and minerals. The specific requirements vary significantly depending on the animal's species, age, weight, and stage of production (e.g., growth, gestation, lactation).
Dry Matter vs. As-Fed Basis
A crucial concept in feed calculation is the difference between dry matter (DM) and as-fed (AF) basis. The as-fed basis includes the natural moisture content of the feedstuff, while the dry matter basis accounts for all water being removed. To accurately compare the nutrient values of different ingredients, all calculations should be performed on a dry matter basis. You must first convert as-fed values to a dry matter basis using the following formula:
DM Nutrient % = AF Nutrient % / DM % of Ingredient (as a decimal)
For example, if haylage has 10% crude protein (AF) and contains 50% dry matter, its crude protein on a DM basis is 10 / 0.50 = 20%.
Method 1: The Pearson Square
For formulating a ration using only two ingredients to meet a specific nutrient target, the Pearson Square method is simple and effective.
- Draw a square. Write the desired nutrient percentage (e.g., protein) for the final mix in the center.
- At the left corners, write the nutrient percentages of the two ingredients you will use.
- Subtract the center number from the larger of the two ingredient values and place the result diagonally across the square.
- Subtract the smaller ingredient value from the center number and place the result diagonally across. Disregard any negative signs.
- The two diagonal numbers represent the 'parts' of each ingredient needed in the final mix.
- Add the parts together to get the total number of parts. Divide the parts for each ingredient by the total parts and multiply by 100 to get the percentage of each ingredient in the final feed.
Example: Using the Pearson Square
To create a 16% protein feed using corn (9% protein) and soybean meal (45% protein):
- Subtract 16 from 45: The result (29 parts) goes diagonally to the corn side.
- Subtract 9 from 16: The result (7 parts) goes diagonally to the soybean meal side.
- Total parts = 29 + 7 = 36 parts.
- Percentage of Corn = (29 / 36) * 100 = 80.56%
- Percentage of Soybean Meal = (7 / 36) * 100 = 19.44%
Method 2: The Algebraic Method
For more than two ingredients or multiple nutrient constraints, setting up and solving algebraic equations is necessary. This method works well for formulating rations with additional supplements like minerals or vitamins.
Step-by-Step Algebraic Method
- Define variables for each ingredient (e.g., let 'C' be the percentage of corn and 'S' be the percentage of soybean meal).
- Set up an equation for the total mix. For example,
C + S + ... = 100%. - Set up an equation for each nutrient target. For example,
(Protein % of C * C) + (Protein % of S * S) + ... = Desired Protein %. - Solve the system of equations to find the percentage of each ingredient. For a simple two-ingredient problem with one constraint, you can use substitution to solve the two equations.
Method 3: Using Feed Formulation Software
For large-scale, complex, or least-cost formulations, computerized methods are the most efficient. This involves using specialized software to process ingredient data, nutritional requirements, and costs to generate an optimal feed formula. Software options range from basic spreadsheets to advanced programs used by large feed mills. They can easily handle multiple ingredients and constraints, providing more accurate and cost-effective results than manual methods.
Manual vs. Computerized Feed Calculation: A Comparison
| Feature | Manual (Pearson/Algebraic) | Computerized (Software) | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Number of Ingredients | Limited (best for 2-3 ingredients) | Unlimited | ||||||||
| Complexity | Simple calculations | Handles complex constraints and multiple nutrients | n | Accuracy | Good for simple rations; prone to human error | Highly accurate, minimal calculation errors | n | Cost | Free; requires only a calculator | Can involve initial software costs |
| Speed | Slow, especially for multiple ingredients | Very fast; instant recalculations | ||||||||
| Optimization | Trial-and-error approach for multiple goals | Automatically finds the least-cost solution |
Beyond the Numbers: Final Considerations
Accurate feed calculation is more than just balancing numbers. It requires considering the following factors:
- Ingredient Variability: The nutrient content of raw ingredients can vary due to soil, harvest time, and processing. Regular testing of feed ingredients is recommended for large operations.
- Palatability: The final mix must be palatable so animals will consume enough to meet their nutritional requirements.
- Feed Additives: Vitamins, minerals, and other additives are often added separately or in a premix to ensure micronutrient needs are met.
- Monitoring Animal Performance: After formulating and mixing a new feed, monitor the animal's health, weight gain, and production levels. Be prepared to make adjustments based on performance.
Further research on specific animal nutritional requirements is advised through reputable sources like university extension publications or the National Research Council (NRC) nutrient recommendations. For example, the University of Nebraska-Lincoln offers excellent resources on feed dry matter conversions: Feed Dry Matter Conversions (G2093).
Conclusion
Calculating feed composition is a fundamental skill for livestock producers aiming for optimal animal health and economic efficiency. While manual methods like the Pearson Square offer a simple solution for basic two-ingredient rations, more complex scenarios benefit from algebraic calculations or dedicated software. By first converting all ingredients to a dry matter basis, considering nutrient variability, and consistently monitoring animal performance, you can create balanced and cost-effective diets that ensure the productivity and well-being of your livestock.
