Sammendrag
Alveld is a hepatogenous photosensitivity disorder in lambs. Although alveld has been known in Norway
for more than 100 years, there are still questions related to the cause of the disease. Phytoporphyrin has
long been incriminated as the photosensitizer in hepatogenous photosensitivity diseases but previous
findings suggest that the photosensitizing mechanism in alveld is more complex, possibly involving other
co-factors. The current work investigates the presence of non-hepatogenous photosensitizers originating
in lamb’s drinking water from various sources. In addition samples of two of the predominent cyanobacteria
found in a representative biofilm (i.e. aggregates of microbes) were identified and isolated in axenic
(i.e. pure) cultures. Information from the absorption-, fluorescence emission-, and -excitation spectra and
the action spectrum for the formation of singlet oxygen was combined in order to identify the chromophores
responsible for the formation of singlet oxygen, e.g. phycocyanins from the cyanobacteria. The highest
level of singlet oxygen formation was detected in lotic (i.e. flowing) water in the period consistent
with the outbreak of the alveld disease in the area. Meteorological data indicate a warm and wet May
with a high radiation exposure leading up to a colder and wet June with an even higher solar irradiance.
The seasonal variation in the amount of photosensitizers in lamb’s drinking water combined meteorological
data can be important to predict the outbreak of alveld.
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