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Why Rotationally Graze?

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Posted Apr. 1, 1998

If you have ever toured one of our facilities you will readily notice that they are divided into many small paddocks and are intensively managed. We forage specialists are strong proponents of rotational grazing. However, some people walk away from our tours thinking that rotational grazing, although interesting and intriguing, is probably impractical and too complicated for most producers.

Others leave wanting to implement an intensive rotational grazing system immediately, thinking that the word 'system' implies simplicity of management. Both scenarios describe unintentional and undesirable results from noble efforts on our part. In reality, a moderately intensive grazing system, using existing pastures when available, is usually a more practical starting point for most producers.

But why rotationally graze? If you answer this question by replying that 'you can increase the stocking rate', then you probably have the cart before the horse and we need to re-think the process. The stocking rate can only be increased as the carrying capacity increases. The primary objective in rotational grazing should be pasture or range improvement using rest periods.

What is the importance of rest periods to the grazed plants? Rest periods allow the grazed plants time to rebuild the photosynthetic factory that was removed by grazing, and to restock the warehouse from which the supplies for the rebuilding process were taken.

The photosynthetic factory is the green leaf material and the warehouse is the root system. If less than 50% of the leaf material is removed, then the plant can rebuild the photosynthetic tissues without a drain on the root system - the warehouse.

However, if more than 50% of the photosynthetic tissue (the green leaves) is removed, the warehouse no longer has the luxury of replenishing its stores while simultaneously rebuilding the factory. The warehouse sacrifices its reserves to bring the factory back to full production as soon as possible. Once the factory is up and running, the warehouse begins the restocking process. The length of time between the grazing event and full plant recovery is directly correlated to the severity of the grazing event: the greater the extent of tissue removal, the longer the recovery process.

For example, let's examine plants under a continuous grazing regime. Early in the spring, most of the plants are green and actively growing. Livestock demonstrate few strong preferences.

As the spring advances toward summer, some plants are beginning to mature with a few producing seeds. Under continuous grazing, livestock avoid the more mature plants and select for the plants that are still actively growing. Many of the actively growing plants are plants that have been previously grazed.

These previously grazed plants have the most palatable plant parts. Livestock select the tender, more palatable regrowth, and graze these plants that have already sustained the most grazing pressure. Livestock preference is usually directed toward the largest plants with the most new regrowth. As summer progresses and as soil moisture usually decreases, most of the plants are trying to produce seed. The larger, more robust plants with the slower recovery rates have more fresh green material since they have a larger, deeper root system.

While other smaller stature plants are senescing or drying up because of lack of moisture, the larger plants are still producing new leaf material although at a slower rate. Livestock continue to selectively graze these plants with the most new regrowth.

Under continuous grazing, the larger plants that have the adaptations necessary to remain actively growing even during adverse soil moisture receive the most grazing pressure over the grazing season. If the larger plants do not have the opportunity to recover after the grazing events, the root systems are steadily depleted. After a few growing seasons, the larger plants become smaller and less robust, their root systems diminish, seed production decreases, and they become less competitive. In time, the more desirable preferred plant dies leaving a place for the less desirable, less productive, smaller stature plants to occupy the space, and hence, rangeland degredation!

How does plant rest improve pastures? Proper rest periods give the more desirable, more productive plants a competitive advantage. Before we explain further, we need to grasp a few basic plantanimal interrelationships that are essential to grazing management.

These are briefly listed as follows:
1) whatever is grazed early in the growing season tends to be grazed throughout the growing season, 2) livestock prefer fresh young material over mature material, 3) livestock prefer leaf material over stem, 4) livestock prefer long-wide leaf plants over narrow-thin leaf plants, 5) the larger the plant, the larger the root system, and the longer the recovery period, and 6) a plant's primary objective is to build a factory that will over the growing season produce the vegetative and reproductive structures to ensure its long-term survival. With rotational grazing, we as grazing managers control the graze and rest periods for the benefit of the more desirable plants. Simultaneously, we attempt to control livestock selectivity by forcing the animals to graze plants during each grazing event that would normally be avoided under continuous grazing. We adapt our rotations to the growing conditions found within the pastures, increasing the rate of rotation under favorable conditions and decreasing the rate under less favorable conditions.

What are some guidelines for proper graze and rest periods? If possible, graze periods should not exceed about seven days during periods of rapid growth (i.e. early in the growing season). We minimize the possibility of re-grazing a particular plant's regrowth during a single graze period in doing so.

Graze periods can be adjusted to exceed seven days as the season advances and plant growth slows. Our rest periods should reflect the severity of the grazing event and the growing conditions within the pastures. Rest periods for good native rangeland pastures will range from 30 to 90 days, and for introduced forage pastures the rest periods will range from 20 to 60 days. Longer rest periods are used when pastures are to be deferred from grazing for reasons such as stockpiling forage reserves or creating a fuel load for controlled burns.

The most important aspects to remember when establishing a simple rotational grazing program are two-fold. First, stock conservatively - do not exceed the carrying capacity. A good rotational grazing system will not compensate for a stocking rate in excess of carrying capacity in the long term. Second, insure proper REST periods. Rest periods that are longer than adequate take precedence over proper graze periods.

We can sacrifice the optimal graze period in order to have a proper rest period. Remember, some rest is better than no rest at all. Therefore, the quantity of pastures should not be a hindrance when initiating a rotational grazing system and establishing proper rest periods. The quantity of pastures (and their production) becomes very important when we begin setting optimal graze periods.

Keep in mind that rotational grazing is as much of an art as it is a science. Although some seem to possess a natural ability or 'feel' for grazing management, all must develop a working knowledge for themselves. The best place to begin your schooling is at your own farm or ranch, not necessarily ours. If you have questions about rotational grazing, contact one of the NF forage specialists.