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Management-Intensive Grazing: Grazing System Design

Determining the Number of Paddocks

The determination of the number of paddocks needed is the crucial first step in establishing the efficiency and sustainability of the MIG system. Indeed, the determination of this number is what distinguishes "grass-farming" from other management philosophies. This is because this is the element of the system that is most considerate of the requirements of the forage being grown.  The optimal number of paddocks is one that provides sufficient time for the livestock to graze their rationed supply of forage (Days of Grazing) AND allows enough time between grazing periods for the forage to recover (Rest Period).

This is summarized in the following equation:
Equation: Paddock Number
When a forage plant is grazed or otherwise defoliated, it mobilizes reserves (sugars, proteins, and other stored nutrients) that have been stored in the root and lower part of the stem. It uses these compounds in the initial stages of regrowth.  Once the plant produces enough leaf area, it begins to replenish those reserves that were consumed during the early stages of regrowth. In a sense, the reserves are analogous to a bank account. However, if the forage plant is defoliated too quickly, it may not be capable of replenishing its reserve. To continue the bank account analogy, if funds are tapped more quickly than they can be saved, the account will soon be empty.  Thus, if an insufficient rest period is imposed, individual plants will eventually die and the stand will begin to thin.

Similarly, leaving animals in a paddock too long may cause the animals to graze the forage too closely to the ground (i.e., some of the stored reserves are consumed).  Moreover, if the animals remain while the forage attempts to regrow, the regrowth will likely be grazed (i.e., regrowth is more palatable and will be selectively grazed), and the reserves will more quickly be depleted. Thus, the days of grazing within an individual paddock must be kept to a minimum. Ideally, the grazing herd should be rotated to a new paddock within 3 – 4 days. (Click here for more on the implications of grazing management on "Forage Physiology.")

Of course, forage species differ in the height at which grazing should be stopped and in the rate at which they recover from defoliation (i.e., being grazed).  Recommended grazing heights and rest periods for individual forage species are outlined in Table 1.

Table 1. Recommended grazing heights for beginning and ending grazing and the recovery period needed between grazing some common forage species.
Crop

Target Height (inches)

Recommended
Rest Period (days)
Begin Grazing
End Grazing*
Alfalfa (grazing types)
10-16
2-4
15-30
Annual Ryegrass
6-12
3-4
7-15
Bahiagrass
6-10
1-2
10-20
Bermudagrass
4-8
1-2
7-15
Clover, White
6-8
1-3
7-15
Clover, Other
8-10
3-5
10-20
Orchardgrass
8-12
3-6
15-30
Pearl Millet
20-24
8-12
10-20
Small grains
8-12
4
7-15
Sorghum/sudan
20-24
8-12
10-20
Switchgrass
18-22
8-12
30-45
Tall Fescue
4-8
2-3
15-30
* Height at end of grazing should take into consideration lower quality forage. Source: Adapted from Forage Pocket Guide, by Don Ball, Garry Lacefield, and Carl Hoveland. 1999.


Finally, the number of paddocks that are employed and the rapidity with which animals are rotated to fresh paddocks greatly influences the efficiency of the grazing system (see the Grazing Efficiency page). Although additional paddocks may improve grazing efficiency (in general), such may also increase the labor involved in developing and managing the grazing sequences. Thorough consideration of the costs involved in developing additional paddocks must be considered (see the Economics page).

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