Rotational grazing is most necessary on perennial pastures, especially if several pasture species like smooth brome and alfalfa are mixed together in the pasture. Without rotational grazing, sheep selectively graze plants they prefer, and avoid other plants. Soon the preferred plants are weakened and the avoided plants crowd them out. As a result, only plants less desirable to the sheep are available for grazing at a future date. Rotational grazing forces sheep to consume some of all plants and allows all grazed plants to recover and regrow while sheep graze other pastures.
Plants vary in the way they respond to rotational grazing.
Legumes like alfalfa respond favorably to rotational grazing because their regrowth usually comes from crown buds located at the soil's surface. Substantial time is needed before this new growth is ready for another grazing. Many perennial grasses maintain some leaves near the soil surface that are difficult to graze. These leaves enable the grass to maintain some leaf area and photosynthesis even during continuous grazing. Thus, while rotational grazing is desirable, it is of less benefit for perennial grasses than for alfalfa.