Written by Rachel Frost and Jeff Mosley, Montana State University Extension
Grazing managers should avoid grazing an area at the same stage of plant growth year after year. Changing the timing of grazing prevents repeated defoliation during critical periods of plant growth, which benefits the plant. The most critical growth stages are when plants are initiating new growth in the spring or fall, and particularly midseason regrowth after grazing. The growth of additional leaves and/or the regrowth of existing leaves requires energy from the plant. The plant also needs to store energy for future growth. The first two or three leaves that appear after a dormant period used energy stored the previous growing season. To produce enough energy to meet both growth and storage needs, the plants need adequate leaf tissue. If grazing managers are unable to change the season of grazing so plants have enough leaf area most years to meet their energy needs for plant growth and storage, then the manager may need to reduce the intensity or frequency of defoliation.
Grazing during winter dormancy has few if any adverse physiological effects on plants unless defoliation intensity and/or trampling are so severe they remove or damage the basal buds that initiate growth the next spring. Also, moderate dormant season grazing may help reduce the buildup of dead plant material above the buds on plant crowns. This can benefit plant growth because more or higher quality sunlight reaches the buds and activates them to grow new tillers. Finally, managers should avoid grazing when soil moisture is excessively high for long periods. The soil can be easily compacted by trampling and become more susceptible to erosion.
Grazing managers should avoid grazing plants too frequently during a single growing season. If plants are given an opportunity to regrow and replenish their stored energy reserves, they can be grazed several times or more during one growing season. Regrowth can be abundant under these conditions:
If defoliation occurs too infrequently, some plants will become choked by too much dead material. Subsequent plant growth will be less than the plant's potential because an insufficient amount of sunlight reaches plant buds to initiate tiller growth, and/or many of the leaves do not receive the maximum amount of sunlight. Long, ungrazed periods also can cause the forage plant's nutritional quality to decline.
Grazing managers should avoid removing too much of a plant's leaf area. Leaf blades are the main sites of energy production for the plant. If the leaf area that remains after grazing is very small or the growing point located at the base of the leaf blade is removed, the plant may be unable to regrow and replenish its energy reserves. This is likely to occur if soil moisture levels are low and not replenished shortly after the grazing event. Also, grazing managers should leave enough residual dry matter to prevent soil erosion and protect the plant's roots and stem bases from excessive cold or heat. Intense defoliation of plants, particularly if it occurs frequently, can reduce a plant's leaf area for a long enough period that the plant cannot store enough energy to form the buds needed for next year's growth and/or sustain the buds through long dormant periods.
Graze the type of livestock best suited for the kind of forage available and the forage's nutritional quality. The amount and kinds of forages that livestock consume depend upon a variety of factors, including species, breed, physiological status, and experiences early in life. Understanding why livestock eat certain plants or parts of plants allows managers to use diet selection as a management tool to direct the vegetation change in plant communities toward management objectives.
Matching the number of grazing animals with the forage resource is an important management decision with any grazing system. Too many animals in a management unit will reduce livestock weight gain, conception rates, and body condition and cause undesired changes in the soil and vegetation resources. The carrying capacity of a management unit is the number of grazing animals that can be supported while maintaining or improving the vegetation and related resources. The actual carrying capacity for any management unit varies across years because annual forage production fluctuates due to variability in both the annual and growing season precipitation and temperature.
One goal of grazing management is to prevent large numbers of animals from congregating in any one location for too long. This is especially important on sensitive areas such as streams and riparian areas. When grazing animals cause soil or plant damage, it is often a problem of poor animal distribution, not too many animals for the management unit. Managers can use several strategies and tools to manage and improve livestock distribution on rangelands.
Grazing animals consume the plant species and plant parts that provide the least disruption to their digestive system and best meet their seasonal nutritional needs. Most plants contain natural chemicals that inhibit digestion when they are consumed above some level. Grazing animals are always trying to optimize nutrient and energy intake and minimize the consumption of chemicals that adversely affect digestion and extraction of nutrients from the forage; hence, the need to selectively consume forage species and plant parts. The performance of individual animals will be best when they are allowed to be picky eaters. However, repeated selective grazing of the same plants typically harms the preferred forage plants. Grazing systems are management tools that attempt to minimize an animal's ability to repeatedly and selectively graze desired plants, while trying to optimize animal performance and plant selection across all forage species.
When properly applied, grazing systems are powerful tools that can help rangeland and livestock managers achieve management objectives related to rangeland and livestock production and ecosystem structure and function. Selection of the proper grazing system depends upon understanding the unique combination of topography, soils, vegetation types, and climate that overlap the management unit. No grazing system is better than any other, but each system is appropriate for specific conditions.
Derived from: "Designing your grazing system" by Jeffrey C. Mosley. Cattle Producer's Library.