OSU Extension Educator, Darke County
Livestock Farmers Dealing With the Results of the Drought
By Sam Custer 

The first thing we may think of for livestock farmers is the lack of availability of feed and the cost of it as we deal with the aftermath of this summer’s drought. But in this article you will learn of a few more concerns. 

If you have planted cover crops and plan to graze, ensile, or make hay out of them to feed to livestock, Marc Sulc, OSU Extension, says you should consider the potential for nitrate toxicity in the forage this year. This could be especially of concern for cover crops planted after corn silage that was stunted by drought and received a good dose of N fertilizer earlier this year. Nitrates can accumulate in about any cover crop, including oat, cereal rye, annual ryegrass, and brassica species. If there is potential for N carryover in fields where you planted cover crops, or if N fertilizer was applied to the cover crop forage, it is advisable to test the forage for nitrate content before you harvest or graze the forage this fall. Recent rains could have promoted a flush of nitrates to be taken up by the plant. To make matters worse, the current cold snap might shut down plant growth (depending on the cover crop species) preventing further accumulation of yield, so high nitrate concentrations will not be diluted out in the plant. So consider the N carryover situation in your fields, and test your cover crop forage accordingly. 

Fall is in the air and Jack Frost will strike sooner or later. When he does, questions always arise concerning the dangers of feeding frosted forages. A very few forage species can be extremely toxic soon after a frost. 

Sulc says the warm-season annual grasses in the sorghum family and other closely related species are capable of becoming toxic to livestock after a frost event. Those species contain compounds called cyanogenic glucosides that convert quickly to prussic acid in freeze-damaged plant tissue. Prussic acid is also known as hydrogen cyanide – the very substance of murder mysteries! 

The potential toxicity after frost varies by species. Sudangrass varieties are low to intermediate in cyanide poisoning potential, sudangrass hybrids are intermediate, sorghum-sudangrass hybrids and forage sorghums are intermediate to high, and grain sorghum is high to very high and is most likely to be toxic after a frost. Piper sudangrass has low prussic acid poisoning potential. Pearl millet and foxtail millet have very low levels of cyanogenic glucosides and rarely cause toxicity. 

Other species that have potential to have toxic levels of prussic acid after frost are Johnsongrass, chokecherry, black cherry, indiangrass, elderberry, and some varieties of birdsfoot trefoil.

 Animals can die within minutes if they consume forages such as the sorghum species that contain high concentrations of prussic acid in the plant tissue. The prussic acid is released from the forage and interferes with oxygen transfer in the blood stream of the animal, causing it to die of asphyxiation. Before death, symptoms include excess salivation, difficult breathing, staggering, convulsions, and collapse. 

Ruminants are more susceptible to prussic acid poisoning than horses or swine because cud chewing and rumen bacteria help release the cyanide from plant tissue. 

Plants growing under high nitrogen levels or in soils deficient in phosphorus or potassium will be more likely to have high cyanide poisoning potential. After frost damage, cyanide levels will likely be higher in fresh forage as compared with silage or hay. This is because cyanide is a gas and dissipates as the forage is wilted and dried for making silage or dry hay.