Fróðskaparrit - 01.01.1993, Blaðsíða 101

NARTHECIUM OSSIFRAGUM-ASSOCIATED PHOTOSENSITIZATION IN SHEEPIN THE FAROE ISLANDS
105
Fig. 2.
Narthecium ossifragum (Faroese: Kattarklógv) plant in
flower.
er injury caused by an unknown toxin is
necessary for the crystal accumulation
which then aggravates the liver lesions.
The liver injury or dysfunction results in
retention of phylloerythrin, a photodynam-
ic metabolic product of chlorophyll pro-
duced by rumen microorganisms (Riming-
ton and Quin, 1933). In areas of skin
scarcely protected by wool or pigment the
effect of sunlight on phylloerythrin causes
oxidative necrotizing changes in the cells
of the skin and adjacent tissues.
The differences in susceptibility between
lambs and adult sheep may be due to dif-
ferences in the metabolism of saponins by
the rumen or intemal tissues. Differences in
glutathione transferase activities or other
cytosolic or microsomal enzyme activities
in the liver have been suggested as the
cause of differences in susceptibility to
alveld (Fláøyen and Jensen, 1991).
Pathogenesis
The saponins from N. ossifragum are either
hydrolysed by rumen microorganisms to
sapogenins, sarsasapogenin being the most
important, before absorption or they may
be absorbed as saponins and hydrolysed to
sapogenins probably by the liver. In the liv-
er the sapogenins are conjugated producing
insoluble salts of episarsasapogenin 13-D-
glucuronide and epismilagenin 8-D-glu-
curonide which precipitate in the hepato-
cytes, biliary epithelium and bile as calci-
um salts (Fláøyeneía/., 1991 a; Mileseía/.,
1993). Whether or not these crystals are the
sole cause of the liver damage has yet to be
ascertained. It is possible that a primary liv-
Clinical findings
Clinical signs are seen only in white sheep
or on the white areas in sheep that are part-
ly pigmented. The salient clinical signs in
photosensitized sheep are increasing rest-
lessness, head shaking, scratching of the
face and ears with the hind feet, and rub-
bing of the irritated skin against the ground.
The skin changes develop rapidly, with
swelling and reddening. The eyelids, muz-
zle and lips become swollen and turgid.
However, the most obvious signs are the
thickened, oedematous, heavily drooping
ears. Soon there is seepage of sticky honey-
coloured semm from the thickened skin
which gradually becomes more and more
desicated. After 1-2 days this forms exten-