While the methods and reasons may differ, one thing every grazing system you might stumble across strives to maintain the pasture so it can be used year after year. We can’t do anything about the most critical part of making sure we have plant growth, moisture. However, grazing properly is within a producer’s control to maintain a healthy pasture.
To understand pasture health, we need to know a bit about how the plants in a pasture function. Each year, plants go through a cycle. Stored reserves start growth and produce leaves to manufacture more energy. These resources are used to reproduce (seeds/vegetative) or stored for next year’s growth. Drought, grazing, mowing, fire; all these events disrupt energy production in the leaves and cause more reserves to be used for regrowth. Most plants have factored in disruptions to this annual cycle and have extra reserves tucked away and can rebound from these events.
When we constantly take away the plant’s ability to produce energy through defoliation, like chronic overgrazing, the reserves get so depleted that the plant’s overall health starts to suffer. Because the plant no longer has energy to spend even maintaining itself, roots are actually sluffed off to reduce energy demands. This leads to decreased nutrient and water uptake by the plant and a longer recovery.
Some of the earliest work done on the effects of grazing was done at the University of Nebraska by John Earnest Weaver from 1932-1952. Weaver and his students would dig trenches of up to 15 feet deep into pastures and prairies, then carefully excavate plant roots in incredibly detailed drawings. His work began laying the groundwork for our understanding of how plants handle grazing, drought and other stresses. In these studies, Weaver noted decreases of up to 60% in root production for plants that had been subjected to heavy grazing. Multitudes of studies across every ecosystem that you could think of have been done since Weaver’s work and they all paint the same picture. Grazing stress causes plants to loose anywhere from 35-70% of their roots.
Knowing this, it’s easy to see how prolonged grazing stress by overgrazing causes pasture productivity to decrease. Plants don’t produce as much growth and the vigor of desirable species lessen. This leaves the door open for weedy or undesirable species to establish themselves and lower available forage even further. If we don’t adjust stocking rate accordingly and let the pasture recover, further overgrazing occurs creating a negative feedback with worse and worse results. Not only do we reduce production, but we now have to spend more money on weed control and other management options like fertilization.
So what do we do? Proper grazing and stocking of pastures is key to maintaining the long-term health of grasslands. As a good rule of thumb, we often say that 50% of the plant should be left behind to maintain vigor, take half - leave half. Of that 50% we allot to animals, only 25% is actually consumed with the rest trampled, fouled, or consumed by insects/wildlife.
How do you tell if your pasture has been grazed enough for the animals to be moved? First, identify key management species you want to focus on. In a smooth brome pasture, this is pretty straight forward: brome. In a native pasture or other mixes, we need to decide what these plants are. Your local extension office or NRCS is a great resource for this step.
After we know the key species to focus on, go out to your pasture and see how much of these have been removed. That 50% we were shooting for earlier is by weight, not height, so visual assessment can be a bit tricky. An easy way to calibrate your eye is to find an intact grass plant and cut it off at ground level. Take this plant and try to balance it on your finger. This can be a bit tricky in the wind, but it doesn’t have to be perfect, just get close. This balancing point is your 50% utilized level. If you look around and see plants have been grazed even lower, balance it again and you get 75% used to compare it to. Do this in several places across your pasture that are fairly representative and you’ll have a good idea of how much plant you’ve been removing.
Overgrazing can be very detrimental to pastures, especially if it’s repeated year after year. By taking the time to assess your pasture’s utilization and rotate animals accordingly, you’ll not only maintain better pasture health, but save yourself some time and effort in the long run.
-Ben Beckman is a beef systems Extension Educator serving the counties of Antelope, Cedar, Knox, Madison and Pierce. He is based out of the Cedar County Extension office in Hartington. You can reach him by phone: (402) 254-6821 or email: ben.beckman@unl.edu .