Bracken Poisoning
One of the other serious illnesses in young stock we are seeing at the moment is Bracken poisoning.While adult cattle are occasionally affected, the majority of cases we see are in young stock from three to twelve months of age, probably a reflection of their size and inquisitive nature. I have often made the observation that paddocks with bracken only along fence lines are associated with poisoning. This could be due to calves tendency to camp in groups close to the fence seeking shelter, bringing them into close contact with something that seems interesting to chew on.
Signs of illness occur after calves have had access to bracken from 2-8 weeks. It is possible for animals to show signs of poisoning for up to 6 weeks after removal from bracken although we rarely see new cases after the first week away from the infested paddocks.
The underground roots and the new curly fronds have up to five times the amount of toxin as the mature plant but it appears that in our area at least, most poisonings are from ingestion of the mature leaves.
The toxin affects the blood causing a reduction in platelets, which are essential for blood clotting and a reduction in the cells that fight infection. The clinical signs that are seen are a manifestation of these two main mechanisms.
Bleeding is seen as blood in the eye, from the nose or in the faeces. The most common sign in heifers is small haemorrhages visible inside the lips of the vulva.
The inability to fight infection results in various overwhelming bacterial infections, such as pneumonia and peritonitis leading to elevated temperatures and severe weakness.
The vast majority of affected animals die, although some do respond to treatment with antibiotics.
The method of control is to avoid the opportunity to graze bracken. This may mean a hot wire in from the fence line and a planned eradication program using spray such as Brush Off.
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