For producers with multiple pastures, the starting point for setting up a rotational grazing system could be as simple as closing all gates and grouping cattle into a single herd. If the situation requires cross fencing to create multiple pastures, more planning is required to begin.
To gain experience with rotational grazing, start with existing pastures. Ideally, forage types would be separated, as well as significant soil delineations (such as range sites), into pastures that have approximately equal forage production. This is more easily achieved with introduced monoculture pastures such as Bermuda grass.
What needs to be considered when establishing a rotational grazing system? Water is one primary consideration. Adequate water must be supplied year round for the herd or herds in each grazed pasture.
Establishing the stocking rate is the next consideration. The stocking rate is based on forage production from acres that can be grazed and can be estimated by determining forage production and allocating it based on livestock demand. Or, begin with your existing cow herd if you are comfortable with your current stocking rate.
A caution: If you plan to use your existing stocking rate, be prepared to adjust herd numbers downward if you find yourself consistently rotating into pastures before appropriate re-growth has occurred. A rotational grazing system does not necessarily grow more grass in the pastures. However, it can aid in correcting grazing distribution or selective utilization (both under and over utilization) within pastures, thus improving grazing efficiencies; it will not automatically increase forage production.
That being said, the next question is: “How many pastures are needed to gain good experience in a planned grazing rotation?”
There is no single answer, but four or five are adequate to start. However, to design a system that allows a pasture to rest about 85 percent to 90 percent of the time, you need eight pastures or more. If all pastures have equal production, theoretically, in an eight-pasture system each pasture would be grazed 12.5 percent of the time and rested 87.5 percent of the time.
The more pastures available in the rotation, the greater the management required. For example, with eight pastures and a 30-day cycle, the grazing length per pasture is about 3.75 days, meaning someone has to rotate cattle on a regular basis. More importantly, someone must be willing to assess the pastures and growing conditions regularly to make adjustments to the rotation as conditions warrant.
So, how are grazing cycles determined? Actual grazing rotation and time allocated in each pasture is determined by proportional production and growth rate of forages in the pastures. Forage production potential is determined by the interaction of forage types, soils and fertility.
Growth rate is determined by season and moisture conditions. Under good growing conditions, rotation is rapid and slows down drastically as soil moisture conditions deteriorate. Introduced or tame pastures such as Bermuda grass or plains bluestem will usually have a shorter cycle length than good-condition native grass pastures under the same conditions. Introduced pastures developed to grow rapidly in response to nitrogen fertility reach optimum balance between quality and quantity much sooner than native grasses such as big bluestem, Indian grass, little bluestem and switchgrass. In a perfect grazing situation, grazing a pasture would occur just prior to when it reaches the point of “diminishing returns” for both forage quality and quantity. The following chart indicates “rules of thumb” for length of grazing cycles relative to Bermuda grass and good -condition native grass by season.
Pasture growth in the spring and early summer should be such that excess forage is present. Introduced pastures may require some to be harvested as hay to capture quality and quantity at optimum conditions. Another option is to lay out of the rotation a pasture or more for a cycle or two and then pick them up in subsequent cycles. The same could apply for the native grass pastures as well.
Hugh Aljoe is a forage specialist at the Noble Foundation in Ardmore, Okla.: www.noble.org