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Management-Intensive Grazing: Grazing System Design

Grazing Equation

Many of the factors that are part of the grazing plan show up in each of the equations that are used to calculate the forage allotment, paddock number, and paddock size. In fact, one could combine all the elements of a grazing plan in one "Grazing Equation."  This allows assumptions about various elements of the grazing plan to be altered so that the effect of those changes on the overall system can be evaluated.

The "Grazing Equation" is possible because the fundamental rule in designing a grazing system is that the number and average size of paddocks must combine in a way that satisfies Equation 1.

Eqn. 1.

Number of Paddocks x Average Size of Paddocks = Available Acres

Since equations are used to calculate the optimal paddock size and the number of paddocks that are necessary (see pages on "Determining the Number of Paddocks" and "Determining the Size of Each Paddock"), those equations can be plugged into Equation 1. After rearranging the elements, the equation reduces to the "Grazing Equation" (Eqn. 2).

Eqn. 2. (large version of eqn. 2)

Animal Weight x DM Intake, % x Head x (Days of Grazing + Rest Period)
Available Forage x Grazing Efficiency, %
= Available Acres

Thus, the "Grazing Equation" can be rearranged to isolate any one of these elements (e.g., the equation could be solved for an appropriate target weight for the animal or the amount of available forage that is needed, etc.).

To save you the trouble of working through the algebra, a Grazing Calculator is available for download here.  This downloadable tool walks the user through the process of answering questions like "How many head can I carry?", "How many acres do I need for the number of animals that I have?", "How many days should I leave the animals in the paddock before I rotate them?", etc..