Eddie Baggs

Beef cattle producers and horse owners should be on the watch for two types of poisoning often associated with dry conditions.

The potential for nitrate and prussic acid poisoning of livestock through grazing standing forages or consuming hay is most often associated with stressful conditions including drought.

Usually, prussic acid poisoning is not a problem with properly cured hay, but livestock owners should be taking precautions with their animals if they have an abundance of Johnson grass, which creates prussic acid risk, in grazing pastures or have highly managed pastures with nitrogen fertilizer applications.

Unlike prussic acid, nitrates will not dissipate through the normal hay curing process.

Both conditions can cause death and should be taken very seriously. However, this does not necessarily mean that this is a problem in your particular pasture. It is a condition to be aware of and depending on risk factors for which forage tests may be merited.

Symptoms of animals affected might include staggering, gasping, salivation, trembling and rapid pulse. Death would be the most acute result.

Even as the outward signs are the same for both nitrate and prussic acid poisoning, each affects cattle and horses in different ways: Nitrate poisoning inhibits the ability of blood to transport oxygen; prussic acid inhibits the ability of cells to take oxygen from the blood.

Nitrate accumulation can occur in virtually any plant with the ability to grow rapidly and use soil nitrogen efficiently. Small grains, millet, Bermuda grass and fescue are forages common to the North Texas area that can potentially cause nitrate poisoning.

The most infamous, however, for both nitrate and prussic acid problems are the sorghums: forage sorghum, sorghum-Sudan hybrids, Sudan grass and Johnson grass.

Many weeds — pigweed, dock, lamb’s quarters, Russian thistle and nightshade to name a few — also can cause poisoning.

Under normal conditions, nitrate in the soil is absorbed by plant roots, transported through the stems, and converted in leaves to proteins and other substances that are useable by the animal.

Nitrate typically is used by the plant about as fast as it is absorbed from the soil. Any condition hindering plant growth can cause nitrate accumulation, mostly in plant stems. Nitrate poisoning occurs when this excessive nitrate is consumed and converted to nitrite faster than the animal can use it. Free nitrate in the rumen is readily absorbed into the blood stream, where it destroys the blood’s ability to absorb and carry oxygen.

Prussic acid is usually attached to a larger sugar molecule and is part of the normal growth process in problem plants. It is not harmful to the animal in this form. Problems occur when environmental conditions, such drought, slow plant growth, causing the sugar molecules to accumulate in the plant. Accumulation is mostly in younger leaves and new growth.

So be observant and look for these plant situations and take proper precautions to prevent drought-related livestock deaths.

EDDIE BAGGS, county extension agent with the Texas AgriLife Extension Service in Denton County, can be reached at 940-349-2880.