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 plantwith 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.
Animals most affected
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
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. perennisis most toxic during its flowering and seeding stages.
Oral doses in kg/day of fresh plant material:
20 (or 2-3 when exposure is over 4-6 days)
0.2-0.3 (over 5-6 days)
fall in milk production (milk appears translucent salmon pink in colour), anorexia;
weakness, apathy, difficulty in walking;
mild jaundice of the conjunctivae; the ammal remaining afebrile throughout.
colic, spasms of the anal sphincter, often severe with tenesmus and frequent
evacuation of excessively liquid faeces.
often delayed in onset;
oliguria with painful urination, albuminuria, haematuria, (true or pseudo, the
urine may be discoloured by red chrysohermidine and be dark red in appearance).
At the height of the poisoning, a definite haematological picture emerges with anaemia,
leucocytosis (lymphopaenia, neutrophilia, eosinophilia).
There may be progress towards a full remission, or death may occur immediately or
after 10-12 days.
jaundice (discoloration of the conjunctivae);
degenerative changes in the liver, hepatic
hypertrophy and necrosis;
renal congestion and/or nephritis;
occasional pericarditis and thoracic
exudation, oedema of the abdomen.
No antidote. Symptomatic care only:
hepatic protective agents;
a blood transfusion undertaken towards the end of the poisoning incident gives
good results (based on observations made and confirmed on numerous occasions
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 150litres per day.