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Management-Intensive Grazing: Grazing System Design

Determining the Size of Each Paddock

Sizing individual paddocks is the aspect of MIG planning where the "grass-farmer" exercises the most control over the system. Like calculating the number of paddocks, the determination of the optimum size for an individual paddock is primarily a mathematical function. In this case, however, the equation accounts for the anticipated or actual amount of forage available per acre (Available Forage), the daily forage need (Animal Weight x DM Intake Rate / Grazing Efficiency), the amount of time the animals will remain in the paddock (Days of Grazing), and the number of animals that will be in the mob (Head). Thus, determining the optimum size for each paddock can be accomplished with the following equation:

Optimum Paddock Size = (Animal Weight x DM Intake, % x Head x Days of Grazing)
(Available Forage x Grazing Efficiency, %)

(large version of eqn.)

In most cases, the paddock size is set during the initial development of a grazing plan and is held relatively constant during the year (e.g., paddock 12 is always 5 acres, paddock 3 is always 7 acres, etc.). Calculating the paddock size in this way requires that values for many of these parameters be assumed.  In these cases, the grass-farmer exercises their control over the system by increasing or slowing the rotational sequence based on forage availability/growth, manipulates the rate of forage growth (e.g., decrease nitrogen fertilization, increase irrigation, etc.), or alters the number of grazing animals (i.e., increase/decrease stocking density).  The most dynamic MIG systems, however, may also simultaneously vary the size of individual paddocks.