Water hemlock poisoning in cattle: Ingestion of immature Cicuta maculata seed as the probable cause

It is well understood that water hemlock tubers are highly toxic to animals and to humans. However, this is the first time that immature seed from (Cicuta maculata) has been implicated in livestock poisoning. Nine mature Hereford cows from a herd of 81 died in northwestern Utah after ingesting immature seed heads of water hemlock (Cicuta maculata) in late summer. No obvious signs of poisoning were reported as all nine were found dead near the banks of the stream where water hemlock was found. Upon discovery of the dead cows, the remaining 72 cows were immediately removed from the pasture and no further losses occurred. Field necropsy of 3 of the dead cows and follow-up serology and histopathological examination of selected tissues did not identify any bacterial or viral causes. History of ingestion of large quantities of water hemlock seed, the acute nature of the deaths, chemical comparison of seed with toxic tubers and follow-up mouse bioassay testing supported the diagnosis of water hemlock poisoning. Seed heads collected from the neighboring pasture upstream and across the fence from the poisoned cattle and tubers collected from grazed plants were chemically analyzed and found to contain cicutoxin, and high levels of two cicutol-like derivatives (cicutol-#1 and #2) as well as other unidentified polyacetylene compounds. Seeds and tubers from suspected plants were semi-quantified and compared to archive samples of highly toxic tubers used in previous experiments. The immature hemlock seed contained less cicutoxin (0.01 times), but 9.5 and 22.5 times more cicutol-#1 and cicutol-#2 respectively, compared to the archive sample. Tubers from the grazed plants contained 4.6 times more cicutoxin and 9.8 and 18.8 times more cicutol-#1 and cicutol-#2 respectively, compared to the archive sample. Mouse bioassays with water extracts of immature seed and tubers from grazed plants demonstrated both were highly toxic and of greater toxicity when compared to archived sample.