One hallmark of MIG systems is rotational grazing, that is, the practice of dividing up available pasture into multiple smaller areas, called paddocks, and then moving the animals from one paddock to the next after a number of days. However, in some instances continuous grazing is an accepted strategy under MIG.
The grazier manages the grazing by determining the number, size, and layout of the paddocks, when to move animals from one paddock to the next, and when to cut hay or provide supplemental feed. Also, the grazier can choose to add or remove animals from the herd to match the herd size to the available pasture.
The decisions are based on estimates of the amount of forage in each paddock, soil conditions, present and forecast weather conditions, season of the year, and condition of the animals. Some MIG operations make objective measurements of forage condition using devices that measure the height of the sward. Others rely more upon personal observation and assessment.
One of the key concepts in MIG is the grazing wedge, which is the range of sward heights where the forage grows most rapidly.
The monthly magazine The Stockman Grass Farmer is a leading forum of MIG ideas. Graze is a primary source of information on dairy grazing and grazing in the northern U.S. Grazing systems relating to the conservation and sustainable management of rangelands is researched by the Society for Range Management.
For farmers and ranchers with cattle in open fields, there is a tendency for the animals to beat down and trample the plants across a wide area. The animals also typically congregate in one area such as around a water tank, feeding wagon, and often in riparian areas where degradation of banks can have negative impacts on wildlife.
This repeated trampling of the same areas over and over destroys plant life faster than it can recover. Eventually sections of the field become a permanent swath of exposed soil. When it rains this turns into muck a foot deep, which in turn covers the animals and makes maintaining sanitary conditions difficult. These exposed tracts of land often serve as seed beds for invasive species of weeds.
The main idea of the paddock is the concept of rest. When a forage plant is grazed, it must regrow from energy created by the remaining leaves, or from energy stored in the roots. If the plant is grazed before it has had time to restore its energy, the plant will be weakened. Rather than the same large areas being repeatedly trampled, the animals are instead forced to only occupy just a small area of the total field inside the paddock. By keeping the animals in this one small area, the trampled and grazed plants in other previously occupied parts of the field are given time to recover and re-establish themselves.
Additionally, constantly moving the animals every few days between paddocks prevents animal wastes from building up to extreme levels in small areas. It also permits time for the wastes to naturally break down so that there is minimal odor from a field of paddocks, as opposed to a feedlot that is constantly trampled into a wet smelly mixture of mud, manure, and urine.