Nitrate is a nitrogen-based compound that is stored in the stems of several different plants, including cornstalks. Any time plant growth is stunted, such as in drought, more nitrate can accumulate. Nitrate ingested by the animal is converted to a toxic form called nitrite, which makes the animal’s blood unable to carry oxygen. Affected animals show weakness, blue mucous membranes, collapse, and death. Signs can start occurring anywhere from 30 minutes to several hours after ingestion. Animals receiving a chronic low dose of nitrate will be less productive, with signs including lowered milk production, abortions, slow growth, and increased susceptibility to other diseases. Nitrate poisoning can be prevented in some cases by cutting stalks higher than normal to avoid the more toxic part of the plant.
Mycotoxins are a class of toxic substances that are produced by fungi. Aflatoxin is one of the most common of these. It is more common in drought years and when corn ears are damaged by insects, etc. Chronic ingestion causes reduced productivity and slow growth of livestock. Additionally, it can make them more susceptible to other diseases as well as cause liver damage. Some laboratory studies have also shown causing cancer in animals.
Forage samples can be sent to Iowa State University or other labs to test for nitrate levels and mycotoxins. Contact us at the clinic, 319-837-6511, if you are interested in finding out more about testing.
Notes from Iowa State University class VDPAM 426 (Toxicology)
Hussein, SH. Mycotoxins. In: Blackwell’s 5-Minute Veterinary Consult: Ruminant. 1st edition. Wiley-Blackwell, Ames, IA. 2008.