With the recent awareness caused by reports of grass causing cattle deaths in Texas (Read about this here), here is a review of some pertinent facts related to this problem.
• Many plants contain cyanogenic glycosides such as Johnson grass, Sudan grass, common sorghum, arrow grass, velvet grass, apricot, peach, black cherry, etc.
• The cyanogenic glycosides in plants yield hydrocyanic acid or prussic acid when plant cell structure is disrupted or damaged, for example, by freezing, chopping, or chewing or in drought conditons.
• The leaves of sorghum or forage grasses may produce up to 25 times more prussic acid than stems. New rapidly growing shoots from young plants often contain toxic levels. Seeds generally do not contain toxins.
• Heavy nitrate fertilization, especially in phosphorus-deficient soils can increase toxicity.
• Spraying of cyanogenic forage plants with foliar herbicides such as 2,4-D can increase their prussic acid concentrations for several weeks after application.
• Grazing stunted plants during drought is the most common cause of poisoning of livestock by plants that produce prussic acid.
• Frozen plants may release high concentrations of prussic acid for several days. Prussic acid from plant tissues declines after wilting.
• Signs can occur within 15-20 min to a few hours after animals consume toxic forage and death can occur within 30-45 minutes of the onset of symptoms. Signs may include: excitability, rapid breathing, rapid heart beat, tearing, salivation, staggered gait, voiding of urine and feces, muscle spasms, bright red mucous membranes.
• Sodium thiosulfate alone is an effective antidotal therapy at =500 mg/kg, IV, plus 30 g/cow, PO, to detoxify any remaining HCN in the rumen.
• Many clinical signs of nitrate and prussic acid poisoning are similar.
• To reduce danger from prussic acid poisoning pasture grasses should not be grazed until they are 15-18 in. tall and forage sorghums should be several feet tall.
• Animals should be turned out to new pasture later in the day and fed prior to turning out.
• Free-choice salt and mineral with added sulfur may help protect against prussic acid toxicity.
For more detailed information about Cyanide poisoning, visit this link.