Mercurialis annua (garden mercury, French mercury). Related species: M. perennis (dog's mercury), M. tormentosa (twisted mercury). A member of the plant family EUPHORBIACEAE. Annual herbaceous plant with creeping rootstock and erect stems. Leaves are small, smooth and light-green in colour. Dioecious, small greenish flowers with hairy capsular fruit. All the species are common weeds, abundant on calcareous soils and in most areas of Great Britain, but not in the Scottish Isles or Ireland.


[affected.gif] Animals most affected
Cattle, sheep.


[etiology.gif] Etiology

Frequent poisonings through repeated ingestion of the plant (during periods of food shortage), or ingestion of contaminated hay or silage.
Note:the fresh plant is unappetizing due to a disagreeable odour and a strong, acrid taste. However, treatment with agrochemicals such as the phenoxy acid herbicides (2,4-D, 2,4,5-T, MCPA) increases the plant's palatability and reduces its bitterness.
In certain regions of France, there is a markedly high level of contamination of corn fodder or silage by the Mercurialis species, which have become partially or totally resistant to the common herbicides (atrazine, simazine) used on this particular crop.


[toxic.gif] Toxicity
Contains several toxic compounds including methylamine, trimethylamine, hermidine (which yields red chrysohermidine on oxidation).
The plant is most toxic during its early phase of growth; M. perennis is most toxic during its flowering and seeding stages.

Oral doses in kg/day of fresh plant material:
LD cattle 20 (or 2-3 when exposure is over 4-6 days)
  sheep 0.2-0.3 (over 5-6 days)



[clinical.gif] Clinical features

General

Gastrointestinal

Genito-urinary

At the height of the poisoning, a definite haematological picture emerges with anaemia, leucocytosis (lymphopaenia, neutrophilia, eosinophilia).

Prognosis
There may be progress towards a full remission, or death may occur immediately or after 10-12 days.



[lesions.gif] Lesions



[treatm~1.gif] Treatment
No antidote. Symptomatic care only:



[case.gif] Case summaries
A herd of 41 cows was put into a field of rye grass which also contained the plants dog's mercury, charlock, chenopodium or fat hen and spurge. Six days later, eight cows were passing dark brown urine and watery faeces. The anal sphincters were retracted. However the cows' temperature and milk production were normal. One cow presented with anorexia and was unable to ruminate; the other animals had diminished appetites. On the seventh day, their urine became dark brown and a further 12 cows had very dark urine. Treatment for piroplasmosis was instituted.
During the following days, the incidence of anorexia became more widespread. One death occurred. On the ninth day, mild jaundice, anaemia, hepatitis and nephritis were recorded at autopsy. By the tenth day, the urine of the animals had become clear again. On days eleven to thirteen, three more cows died. From the fourteenth day onwards, the condition of the remaining cows began to improve.
In summary: out of 41 animals, 27 presented with dark brown urine and 4 died; the overall milk production of the herd went down by 150 litres per day.