William P. Shulaw DVM, Extension Veterinarian; Kent H. Hoblet DVM, Extension Veterinarian; Diane F. Gerken DVM, Veterinary Toxicologist.
Reminiscent of 1988, we are facing possible problems with feeding drought-stressed plants and potential toxic plant consumption by animals that are short on feed because of the drought. Recently, the Ohio Department of Agricultures Consumer Analytical Laboratory has announced free testing of corn/corn silage for nitrates because of the drought. Although not all areas of Ohio are affected, most concerns center around animals being fed, or allowed to graze, stressed plants or plants not normally used for animals. This article will focus on nitrate toxicity but cyanide (prussic acid toxicity) and the consumption of toxic plants by animals are also a concern during drought periods.
Nitrate, itself, is not highly toxic. Problems develop when nitrate (NO3) is converted to nitrite (NO2) in the ruminant animals digestive system. Plants normally convert soil nitrate to plant protein However, when stressed by dry weather, plants may be unable to totally effect this conversion and nitrates may accumulate. In the live animal the nitrite which is formed binds to the hemoglobin molecules in red blood cells and produces methemoglobin which prevents oxygen transmission to tissues and cells.