What is Prussic Acid Poisoning?
- Prussic acid, or hydrocyanic acid, is absorbed from digested feed into the cow/sheep where it attaches to haemoglobin, taking the place of oxygen in the blood.
- This causes following symptoms in the animal: within 15-20 minutes you may see symptoms including staggering, laboured breathing, spasms and foaming at the mouth. Affected animals often lie down, stretched out, and may thrash about. Mucous membranes and blood will be bright pink.
- If levels are high enough, or treatment is not administered quickly, the only symptom you may see is a dead animal.
- Horses, pigs and other non-ruminant animals are less affected by prussic acid because their stomachs convert it to less toxic formic acid and ammonium chloride.
Prevention and Treatment
- Prussic acid poisoning can be treated effectively if the treatment is administered immediately after the first poisoning symptoms appear.
- Feed with higher levels of prussic acid can be mixed at low levels and fed as part of a total ration, to slow down the rate of prussic acid entering the blood.
- Introduce stock slowly to feed (eg. over several days) and do not allow hungry stock to gorge on the product.
- Some licks and supplements can assist. Talk to your advisor or input suppliers.
- Feed Central recommends that you conduct your own research including web and via your regular advisors.
How Does It Build Up in Plants?
- Prussic acid is present in most sorghums, but some species and varieties contain less than others. It is also present in other plants in the sorghum family, such as Johnson Grass, Sudan Grass and Shattercane and some members of the Couch family, Native Fuschia, some Acacias, Rosewood and Linseed meal.
- Most of the prussic acid in plants exists as a non-poisonous chemical called dhurrin (Rhykerd, n.d.).
- Also present in the sorghums is a material called emulsion, which, under certain conditions, can react with dhurrin to form prussic acid (also referred to as hydrocyanic acid). If plants are damaged, such as by freezing, chewing, insect damage, heat stress, wind damage, crushing or trampling, the emulsion-dhurrin reaction is enhanced, freeing larger quantities of poison (cyanide) (Rhykerd, n.d.).
- Once converted, the poison is known as ‘free cyanide’, Free cyanide can evaporate gradually from the plant, but only to some extent, There is still the potential for further release of stored cyanide if the dhurrin/emulsion reaction occurs. This also occurs due to chewing and in the rumen (due to bacteria breaking down the plant cells) and allowing this emulsion/dhurrin reaction to produce prussic acid.
- Prussic acid is extremely poisonous. A concentration of free cyanide plus dhurrin (known as total cyanide) greater than 0.1 percent (1000 ppm or mg/kg) of plant dry matter is considered highly dangerous. (Rhykerd, n.d.)