The basis 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.
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 assesment.
One of the key concepts in MIG is the grazing wedge, which is the range of sward heights where the forage grows most rapidly.