Hot and Dry Conditions Increase Health Threats to Livestock

Prussic acid poisoning is caused by cyanide production in forage sorghums, grain sorghums, sudangrass and johnsongrass.
( Troy Walz, University of Nebraska )

In addition to heat stress, and potential shortages of forage and water, hot, dry, weather can have other negative effects on livestock that can be much more severe. The likelihood of problems from three potentially deadly threats: blue green algae, nitrates, and prussic acid all increase because of hot, dry weather.

Blue Green Algae

Blue green algae blooms are favored by warm stagnant water. Despite the name, the organism that causes the problem is actually a photosynthetic cyanobacteria, not algae. The breakdown of these cyanobacteria after a bloom releases toxins which can be harmful to animals, amphibians and humans.

A pond containing a harmful blue green algae bloom is usually covered by a scum that looks like bright green paint, but other colors varying from blue-green to gray are possible. Water from a pond with blue green algae will have an unpleasant odor. Sometimes the toxins can kill small animals or amphibians which drink from the pond.

If blue green algae is suspected the first recommended step is to conduct a jar test. The procedures to take a jar test are listed at this link http://bit.ly/JarTest If a jar test doesn’t alleviate concerns the next step is to restrict cattle access to the pond and/or submit a water sample to the Kansas State Veterinarian Diagnostic lab for analysis. Please call (620) 784- 5337 for the procedures to collect the sample. An excellent K – State Research and Extension publication on blue green algae is also available at http://www.bookstore.ksre.ksu.edu/pubs/MF3065.pdf 

Nitrates

Nitrates can be a problem in crops such as corn, sorghum, canola, cereal grains,

and some grasses during exposure to drought. The aforementioned crops take up more nitrates than they use during poor growing conditions, resulting in a potentially toxic accumulation of nitrates in the lower portion of affected plants. The ingestion of high nitrate feedstuffs by animals can reduce the ability of the blood, of affected animals to carry oxygen, causing asphyxiation.

Management practices to avoid problems with nitrates include: 

Waiting for a period of good growing conditions to allow nitrate levels to return to safe levels prior to grazing or harvesting for hay.

  • Ensiling the crop reduces nitrate levels from 30 – 60 percent. 
  • Raising cutting height to leave highest nitrate part of plant in field.
  • Grazing animals select lower nitrate leaves and stems instead of higher nitrate lower stems if adequate forage is available.
  • High nitrate feeds can be diluted with lower nitrate forages and grains. 

Prussic Acid Poisoning

Prussic acid poisoning is caused by cyanide production in forage sorghums, grain sorghums, sudangrass and johnsongrass. Unfortunately, for livestock producers the symptom of prussic acid poisoning is often rapid death of the animal. Lush regrowth after stress has the most potential to have excess levels of prussic acid.

Restricting cattle access until new growth and or suckers are 18 inches tall or taller and not grazing johnsongrass, sorghums and sudangrass immediately following or during drought stress can greatly reduce potential for problems. Prussic acid leaves the plant when it dries, therefore prussic acid is not a problem in properly cured hay, but it can be a problem in freshly chopped forage.

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