AgriLife Extension Extras
Published July 27, 2012 @ 6 a.m.
I have had a few calls over the last couple of weeks about grazing johnsongrass. Here is some general information concerning this topic.
Livestock producers can quickly lose animals if forage is not carefully monitored especially when pasture conditions in the area are continuing to decline due to droughty growing conditions. This has resulted in most pastures starting to have a late-summer appearance. One “forage” that seems to be surviving the drought and doing quite well, in many areas, is johnsongrass. With the lack of adequate grazeable forage, what is the possibility of grazing johnsongrass?
Johnsongrass is very competitive with other forage if left unchecked. It is also drought tolerant and is often one of the last plants to stop growing during a drought. Johnsongrass yields can approach 3 to 5 tons/acre under good growing conditions. Nutritive value estimates of 10% crude protein and near 60% TDN are common. In addition to nitrate toxicity potential, another potential negative to utilizing johnsongrass is that it has high potential to produce hydrogen cyanide (HCN). This is more commonly known as prussic acid. The forages used are most likely to produce toxic levels of HCN are the grain sorghums, johnsongrass, sorghum-sudangrass hybrids, and sudangrass.
During droughts, grazing pastures that are mainly johnsongrass should be avoided, if possible. Do not rely solely on drought-damaged forages as the only source of forage. It is important to keep some other form of dry forage available at all times.
- Testing for prussic acid- especially during dry periods after small rain events.
- Do not graze cattle if they are hungry. Feed hay and begin grazing in late afternoon.
- Restrict grazing until plants are at least 24 inches tall. Young, succulent growth and regrowth has greater concentrations of HCN than more mature growth.
- Do not graze regardless of height within four days following a good rain. This is the time when rapid, new growth of young plant tissue occurs.
- Do not graze wilted plants or plants with young regrowth; ribbon-like appearance on the leaves is normally an indication of prussic acid. The best management practice will be to harvest this as hay
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