Prussic acid poisoning can occur when cattle eat cyanide-producing compounds in the immature leaves of sorghum grasses or leaves of cherry and related species of fruit trees. This is most likely to happen after extreme weather conditions such as drought or frost.
In southwestern Missouri, more than 70 adult cattle died shortly after being released into drought-stressed pasture with lush new growth of Johnson grass. Within a few hours of grazing in this pasture, several cows suddenly lay down and died or staggered briefly before collapsing and dying. Few other clinical signs were observed.
Necropsies of 10 of the dead animals showed varying degrees of bright, cherry red blood. This is commonly observed in prussic acid poisoning because cyanide inhibits aerobic metabolism and prevents oxygen in the blood from being released to the tissues.
Though it can be challenging to accurately measure the presence of cyanide in postmortem samples, prussic acid poisoning remains the most likely cause of death.
Sorghum forages can accumulate nitrate in their stems, especially in response to drought, and cyanide-producing compounds in their leaves, particularly in rapidly growing immature plants. Prussic acid poisoning from these annual forages happens most often when abundant rainfall interrupts or immediately follows a drought.
Producers should take the following precautions to prevent prussic acid poisoning in cattle:
• Take soil samples before applying nitrogen to pastures. Excess nitrogen increases risk of both prussic poisoning and nitrate/nitrite poisoning.
• Wait to graze sorghum varieties until they reach a height of at least 24 inches.
• Do not turn hungry cattle into pasture with sorghum grasses. Fill them up on other grass or hay during the day before gradually introducing them to sorghum pastures. Don't turn the entire herd onto a new pasture at once. Consider using test animals if you have not tested for nitrates or cyanogenic potential.
• Remove animals immediately from pastures when an animal is found dead. Consult your local veterinarian and extension specialists about the need for animal necropsies and forage testing.
By taking these precautions, producers can help protect their cattle from prussic acid poisoning.
Photo Credit: istock-mailson-pignata
Categories: Missouri, Crops, Sorghum, Livestock, Beef Cattle, Weather