Grazing Drought-stressed Crop Residue
The UNL U.S. Drought Monitor pegged September as abnormally dry to severe drought in the majority of Nebraska. Therefore, grazing drought-stressed crop residue and moisture-stressed pivot corners may be used as alternative feed options despite possible risk of nitrates from droughty corn and sorghum plants and rapidly declining residue quality. Also, shorter grass pastures may be motivating producers to begin earlier fall crops residue grazing.
When it comes to stalks residue, grain sorghum stover will retain nutrient grazing value longer than corn. This year, earlier residue grazing of corn and sorghum residue soon after grain harvest may provide good nutrition for mid- to late-gestation cattle. Although both residues provide the highest nutrient content soon after grain harvest, prioritize grazing cornstalk fields first. Corn leaves tend to detach from stalks within one to two months after harvest and then blow out of stalk fields; thus, lowering grazing nutritional content. In contrast, grain sorghum stover leaves remain attached to stalks much longer into the winter and early spring.
Previous grain sorghum yields can be used to set optimum grazing stalking rates. For example, set grazing rates to 1 acre per cow per month for every 100 bushels of harvested sorghum. Droughty fields may have less than half the normal grazing rates. Unlike corn residue, grain sorghum stover may have prussic acid toxicity risk along with possible nitrate especially if cattle are forced to graze the lower eight inches of drought-stressed stalks. To reduce risk, do not force cattle to completely graze lower stalks, and delay initial cattle turnout into stressed stalk fields until afternoons with at least partially filled rumens. To reduce prussic acid risk, limit or delay grazing of stover if tiller regrowth is occurring at the base of sorghum stalks or wait until killing plant frosts to graze. OR, pause grazing stressed sorghum stalk fields for one week following the first fall frost where temperatures do not drop low enough to actually kill sorghum.
For more drought management, visit CropWatch, UNL Beef or the U.S. Drought Monitor.
Considerations for Fall Grazing Annual Forages
Fresh forage options in the fall often come with strings attached. While the potential for high quality grazing is present, knowing the risks that may come along is critical to make the most out of these forage resources.
The two main drivers of risks for fall grazing come from the environment, freezing temperatures and drought. Let’s look at drought first.
When moisture is lacking, plant growth is slowed. This is a major obstacle for establishing fall forages but can cause problems with already growing plants too. Cover or forage crops planted during the summer may begin accumulating nitrates as dry weather slows growth. This is especially true for forages that planted into an already fertilized row crop that was hailed out.
Cold weather can be a cause for concern too. As temperatures drop, growth slows, and nitrates can build up again. When plant cells freeze, they can burst, making nutrients more readily available. In high quality forages, this can lead to bloat, especially early in the morning when forage moisture is highest.
In sorghum species including sudans, ruptured cells due to freezing is a bit more serious. This damage releases prussic acid a cyanide compound, which can be deadly to livestock if consumed in high enough quantities. While it can dissipate out in five to seven days, each time more of the plant is damaged by frost, prussic acid is released.
Fall forages can be a great grazing opportunity but need to be managed carefully to be safe. Watch for nitrates during dry weather and nitrates, bloat and prussic acid in sorghum species as temperatures drop to get the most out of your fall grazing.
