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Seeds in Season | November 2023

Manage Plants for Fall Grazing: Nutrition and Prussic Acid

contributed article by Justin Fruechte, Product Expert - Ag

Millborn Seeds, Brookings, S.D.

Two of my favorite times of year are getting pairs on pasture in the spring and turning cows on corn stalks in the fall. As cattle producers the seasons dictate our actions, and these turnouts seem to be representations of changing seasons. I love the sense of gratification and contentment on both the cows’ and my part when the first corn cob is rolled around in their mouth. Without question, grazing stalks is the most popular fall and winter feed strategy, but I want to highlight a few other less common, but just as effective, ideas.

Fall rains in much of the Midwest have pushed new growth as well as re-growth on forage fields. Optimizing lush growth and minimizing potential risk of re-growth is important. As cattlemen we are good at managing our herd, but we also need to manage the plants the herd is consuming.

Cover Crop Blends

If you planted a cover crop blend including species such as turnips, radishes, rapeseed, and cereal grains, you have a highly digestible high protein diet for your cattle to consume. Cattle will gain weight while grazing these fields, so be mindful of how you can prioritize the class of livestock grazing it. Thinner, first-calf heifers thrive on these. Or, if fences allow for it, keep your weaned calves here and let them gain well while grazing.

The important management pointer in this scenario is to maintain adequate dry matter intake levels. Brassicas and lush new grass growth have little fiber and are nearing 80 percent moisture levels. Offering access to corn stalks or hauling out a wagon of grass hay will allow your cattle to buffer their ration with dry forage.

Warm Season Annuals

Another fall grazing opportunity can come from warm season annuals including forage sorghum, sorghum-sudangrass, and millets. If planted early, these were likely harvested once and now the millets and sudangrass hybrids are re-growing. The two common concerns with grazing warm season annuals are nitrate and prussic acid poisoning.

Millets are prone to high nitrates, but not prussic acid. If a plant is stressed from drought, hail, or extremely fast growth it can’t properly photosynthesize to convert the nitrogen it’s taking in from the soil.

Prussic acid is common in forage sorghum and sorghum-sudangrass. This is commonly seen when damage is done to the plant, typically after a frost. Cell walls in the plants burst causing prussic acid to build up in the plant, and when consumed by cattle it results in cyanide poisoning.

So, for management pointers, don’t graze re-growth until it is over 24 inches in height and wait 10 to 14 days after a frost to graze. Prussic acid is a gas and does dissipate from the plant, so when that 10 to 14 day wait period has lapsed, don’t be afraid to graze. Testing for both nitrates and prussic acid is available to give you an accurate answer of levels.

Obviously, we all want to graze as long as possible to minimize winter feed costs. Strategize placing the correct class of livestock with their forage needs to be efficient with grazing utilization. Taking the time in the fall to manage plants will always pay back with less feeding days in the winter.

Photos courtesy Millborn Seeds

Millborn Seeds, Brookings, S.D.

The team of folks at Millborn Seeds have roots that run deep in farming, agriculture, and in the overall respect for the landscape. They opened their doors in 1987 and continue to walk alongside farmers, ranchers, and landowners across thousands of acres throughout the Midwest.

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