Rotational grazing has the potential to double your forage yield. Even the simplest form, using a single cross fence to split a pasture in two, will significantly increase production. Rotational grazing focuses on taking the best possible care of the grass and is based on the plant's physiology. It allows plants the time for recovery and regrowth. Paddock design including he location of water and fencing are critical for successful rotational grazing. The shorter the grazing interval, the smaller the area, the more potential yield that can be captured. The idea arises from not thinking of the size of the field, but the grazing pattern. Typically cattle will graze the best grass first and as that grass starts to regrow tender leaves, they come back and graze that again instead of moving on to more mature plants. So in large field you have the best grass getting overgrazed and other grass is getting undergrazed. This behavior leads to killing the best plants and giving weeds the opportunity to get established. When the pasture is small enough relative to the number of grazing animals, they will graze the field uniformly. In our area, plants recovery will begin in about 3 days after grazing and it will attempt regrowth. If a plant trying to recover is grazed again it will cause significant harm and force the plant to struggle. Optimal rotational grazing would require the animals be moved in 3 days or less, although that rotation frequency may not be practical for many producers.
For grasses to recover easily they should not be grazed below a certain height, those levels are as follows: orchard grass 4", tall fescue 3-4", ryegrass 3", and bluegrass 2". Legumes like clover and alfalfa can typically be grazed lower because of their roots they will be able to recover. Orchard grass and alfalfa have a crown or growing point that must not be damaged if the plant is too survive. Choosing a grazing variety with a low crown will make up for an overgrazing even that might have thinned out the stand. When animals are rotated while the plants are still at the correct height or taller, the plant will recover much, much faster. Beyond that point its not in recovery mode, but survival mode. The plant no longer has enough leaf surface to capture sunlight to rebuild with. The roots will die back and the plant will struggle to repair itself. It will lack the response that can be seen in taller plants.
The recovery period is another important aspect of rotational grazing. During the spring growth surge rotation should occur every 2 weeks to keep the grass from getting too mature. In the summer slum, the recovery period should be 4 weeks. This would not fall into the optimum rotational frequency, but it is worth mentioning because it makes the seasons relative. Cool season grasses will normally need twice as long to recover in the summer. Completely recovered grass will have grown 3 or 4 mature leaves since the last grazing period. It is estimated that it will take between 20 and 60 days for our area. The variability depends on temperature, rainfall, photoperiod, the grass stand, the time of year, and the amount of residual grass left behind from the previous grazing period. Paddock size should reflect a rotation schedule that will be long enough to allow the grass to completely recover before moving the animals back into the paddock.
Relative to paddock design, water placement is the most important thing because it determines how many paddocks you have. The layout of the permanent fence is also important. It is a very good idea to place wood post at a distance so that you can mark off an acre, or a similar measure. This will let you measure the height of the grass and convert it to tons per acre. Having an estimate of the tonnage will allow you to estimate how many days of grazing you have left, which is a very useful tool especially in a drought.
Paddock size can be quite flexible when using polywire and step-in posts as boarders in a larger field. When you have a set number of days the animals will be in one place before the next move, and you can estimate the tonnage based on grass height, you will be able to determine how much space the animals will need for that grazing period. Estimating tonnage is based on several assumptions please see the UKY article below for reference. As an example if you have one acre of fescue that is 12" tall and you wanted to keep a 4" stubble, you would have 8" of available forage. If you make the assumption that you have 200lb dry mater per inch of grass, you would have 1600lb per acre. Cattle should eat about 2.5% of their body weight. So a 1200lb cow would eat 30lb per day. If the herd were 20 cows, they would need 600lb per day. So one acre would give them 2.67 days, or if you wanted a 7 day rotation, you would need a 2.63 acres for one week. Because the condition of grass is constantly in flux, polywire allows you to change the size of the paddocks and keep the same number of days for the rotation schedule.
Photo: This portable fence charger is homemade using a Speedrite 1000 with 10W solar panel.
An excellent book:
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More about measuring the amount of forage in a pasture: www2.ca.uky.edu/agcomm/pubs/agr/agr191/agr191.pdf
More about controlled grazing: pubs.ext.vt.edu/418/418-012/418-012.html
This is an app for apple and android for rotational grazing: