Producers all across the state are busy preparing for the summer grazing season. You have likely worked your calves or received your stockers, and have repaired fences around your summer grass. You have probably finished up your burning and are just waiting on some warm days to get the warm-season grass growing. Additionally, you may also be starting to worry about how much more sericea lespedeza you will have this year or how much closer it is getting to your ranch.
Producers in the western part of the state may think sericea lespedeza is a southeastern-Kansas problem; however, this invasive perennial legume can be found in all but nineteen states in the US. Affecting over 620,000 acres in Kansas, sericea has been reported as far west as Meade county. In the southeastern US it is regularly planted as a forage crop but this is on level ground that can be farmed and easily managed. When properly managed, sericea lespedeza can be used as a viable feedstuff for grazing livestock.
Unfortunately in Kansas where much of our agricultural land is very rugged, this invasive species can be difficult to keep in a stage of growth that is palatable to cattle and quickly becomes an expensive nuisance. When allowed to grow and spread unchecked, it can completely shade out native forage plants.
Sericea lespedeza has high levels of protein; it also has high levels of condensed tannins. Condensed tannins bind with dietary protein in the gut and render it unavailable to ruminal microbes. Tannin levels in sericea lespedeza increase with maturity and under drought conditions, thus the plant is only palatable to cattle while the plant is young and tannin levels are low. Cattle that consume mature sericea experience a build-up of tannin-protein complexes in the rumen that triggers a negative postingestive feed back which can be likened to a belly ache, suppressing forage DMI substantially. Cattle quickly recognize they get this belly ache after consuming the mature plant and develop an aversion to it. The timing of these events coincides with the stages of plant growth where budding, flowering, and seed formation are taking place, thereby increasing the amount of sericea seed that will enter the seed bank for next year's growing season.
It is generally recommended that for sericea to be utilized by cattle it should be aggressively grazed in the early growing season under management-intensive grazing or intensive early stocking. It seems that cows will more readily consume the sericea in its early growth stages than will stockers.
Previously, it was believed that sun curing sericea lespedeza decreased condensed tannin levels to a degree that it would again be palatable. Current K-State research has shown this to be untrue. Cows fed a diet of prairie hay contaminated with sericea lespedeza had much lower forage intakes compared to cows fed uncontaminated prairie hay, presumably the result of the belly ache associated with tannin build up in the rumen.
Further study found that if cows were supplemented with something to prevent the belly ache caused by consuming sericea lespedeza, cattle would readily consume contaminated hay at normal intake levels. In this case corn steep liquor, a cheap and readily available byproduct of corn syrup production was used. When corn steep liquor was offered along with contaminated hay, it bound the tannins and prevented the negative effects of tannin consumption.
Control of sericea lespedeza will take an integrated approach. Such a program may include burning, (which encourages seed germination, kills young plants and removes old growth), mowing (where practical), intensive early stocking, grazing the plant while tannin concentrations are low, herbicide application, and strategic supplementation of cattle with tannin-mitigating compounds. Control of sericea lespedeza will take time and unfortunately we likely won't eradicate it completely; however, we can keep it at manageable levels if we take an integrated approach to control. The future of forage-based beef production in Kansas may depend on it.
For further details on the research mentioned above see the March 2011 Beef Tips or a more indepth report is available in the 2011 Cattlemen's Day publication at http://www.drovers.com/sites/default/files/SRP1047.pdf in the article: Voluntary Intake of Prairie Hay Contaminated with Sericea Lespedeza (Lespedeza Cuneata) by Beef Cows. The publication "Sericea Lespedeza: History Characteristics and Identification" can be found at http://www.drovers.com/sites/default/files/mf2408.pdf.
Source: Arturo Pacheco, Research Associate KSU Cow/Calf Unit