Plant Poisoning Containing Hydrocyanic Acid in Cattle in Southern Brazil
Authors: Gris Anderson , Bavaresco Lucas Henrique , Perosa Fernanda Felicetti , Gomes Teane Milagres Augusto , Fronza Nei , De Oliveira Juliano Rossi , Peripolli Vanessa , Surian Cesar Rodrigo de Souza , Gasper André Luís de , Mendes Ricardo Evandro 
Published: June 2021

Background: Cyanogenic plants accumulate cyanogenic glycosides and release hydrocyanic acid (HCN). In Brazil, there have been reports of several plants that cause HCN poisoning in animals and lead to a fast death with few clinical signs and lesions on post-mortem examination. Some cultivars of Cynodon spp. grasses cause HCN poisoning in cattle in Brazil. The objectives of this work were to report the occurrence of deaths by HCN poisoning in cattle as diagnosed by the veterinary pathology laboratory, describe the quantity of HCN in some cultivars of Cynodon spp., as well as, to describe one cultivar of genus Cynodonnever reported as poisonous.Materials, Methods & Results: The archives of the Veterinary Pathology Laboratory (LPV) at the Concórdia Campus of the Instituto Federal Catarinense (IFC) were reviewed, seeking cases with a diagnosis of hydrocyanic acid poisoning in cattle after post mortem examination. The amount of HCN present in some cultivars of the Cynodon genus was quantified due to the high frequency of poisoning cases. From the 1,235 post mortem examinations of cattle 28 (2.27%) were diagnosed with spontaneous hydrocyanic acid poisoning, 17 cases (60.7%) due to ingestion of Prunus sp. or Manihot sp., and 11 cases (39.3%) of Cynodon dactylon ingestion. Most animals were found dead, normally having presented no clinical signs. Macroscopic evaluation mainly showed a severe amount of unchewed and undigested leaves or grass mixed in the ruminal content presenting a bitter almond odor. It was possible to infer that, among cultivars of the Cynodon genus, Florakirk showed the highest levels of HCN compared (P < 0.05) with Star of Puerto Rico, Tifton 68, Tifton 44, and Coast-Cross. Furthermore, Tifton 85 and Jiggs showed undetected levels of HCN. Leaves showed the highest HCN levels when comparing different parts of the plant. Regarding conservation methods, hay showed undetectable levels of HCN.Discussion: To the best of our knowledge, this work is the first description of HCN poisoning in cattle due to ingestion of Cynodon dactylon cultivar Florakirk. This condition is described with a fast-clinical course, with animals found dead with no premonitory clinical signs. Poisoned animals did not develop macroscopic or microscopic specific lesions. Poisoning can be suspected when animals die suddenly, with absence of lesions under necropsy, and large amounts of unchewed and undigested leaves or grass inside their forestomaches. The diagnosis can be established performing the Picrosodic paper test, either in the pasture, or in the ruminal content. Occasionally however, HCN can go undetected when this chemical compound volatilizes between death and necropsy after several hours. Of all the Cynodon cultivars evaluated, Florakirk was the most dangerous for animals. In contrast, Tifton 85 and Jiggs released no HCN. Leaves were the part of the plant presenting the highest concentration of HCN. This is a defense mechanism that the plant develops against the ingestion by animals. This condition can cause great economic losses to farmers with the loss of animals and the need for prevention by using cultivars without HCN or hay, as 2.27% (28) of deaths diagnosed by the Veterinary Pathology Laboratory in the west of Santa Catarina, Brazil, were due to HCN poisoning. Notably, Florakirk cultivar was identified as the most dangerous cultivar tested, with higher levels compared with Tifton 68. The Star of Puerto Rico cultivar showed similar levels of HCN as Tifton 68. Both cultivars are commonly cultivated in many farms in the south of Brazil.