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If the photosensitisation is secondary (hepatogenous), icterus may be present. Other signs may include those consistent with hepatic encephalopathy such as head-pressing, circling, and behavioural changes.
If the photosensitisation is secondary (hepatogenous), icterus may be present. Other signs may include those consistent with hepatic encephalopathy such as head-pressing, circling, and behavioural changes.
[[Image:Bovimpaction.gif|right|thumb|125px|<small><center>Impaction of a bovine oesophagus (Courtesy of Alun Williams (RVC))</center></small>]]
==Diagnosis==
==Diagnosis==
The history and clinical signs of affected animals are important in order to differentiate whether the condition is primary or secondary. In the case of primary photosensitisation there is often a history of exposure to plants containing photodynamic agents such as St. John's Wort or clover. Alternatively, there may be a history of administration of drugs such as phenothiazines, sulphonamides or tetracyclines. Signs of liver disease are usually absent.
The history and clinical signs of affected animals are important in order to differentiate whether the condition is primary or secondary. In the case of primary photosensitisation there is often a history of exposure to plants containing photodynamic agents such as St. John's Wort or clover. Alternatively, there may be a history of administration of drugs such as phenothiazines, sulphonamides or tetracyclines. Signs of liver disease are usually absent.