Hay made from wilted forage sorghum and fed to hungry cattle in assembly points may cause cyanide poisoning. All sorghums have cyanide producing potential especially after a check in growth. Once produced, toxin will persist even after plant material has been harvested and baled into hay. After ingestion, cyanide is rapidly absorbed into and distributed around the body where it halts use of oxygen at the cell level. This causes oxygen retention in the blood where saturation levels give it an unmistakable cherry red appearance.
Cattle are more susceptible to poisoning than sheep.
Signs appear within an hour of toxic feed being consumed. The prominent signs are respiratory distress, muscle twitching, staggering, cherry red mucous membranes and rapid death. At necropsy the blood is cherry red, later becoming dark red. The rumen content may smell like bitter almonds. The main differential diagnosis is nitrate-nitrite poisoning, which also causes respiratory distress and rapid death but the mucous membranes and blood are chocolate brown instead of cherry red.
Laboratory confirmation is by chemical demonstration of cyanide in the fodder or rumen content. Specimens must be submitted frozen to prevent hydrolytic decline in concentrations during transit.
Immediately prevent access to the suspect hay and offer an alternative low risk feed to dilute toxic feed already ingested. Handling must be minimal to reduce oxygen demand. Urgent treatment with intravenous sodium thiosulphate at 660mg/kg may be life saving in severely affected animals. Follow-up oral dosing with 60g in 600 mL of water at hourly intervals until fully recovered is recommended to prevent relapse. Note that sodium thiosulphate is not registered in Australia for use in food-producing animals.
Sorghum hay can be tested for dangerous cyanide concentrations. Potentially toxic sorghum hay can be diluted with other types of feed