Fróðskaparrit - 01.01.1993, Page 100

104 NARTHECIUM OSSIFRAGUM-ASSOCIATED PHOTOSENSITIZATION IN SHEEP IN THE FAROEISLANDS
69° 42’ N, in the British Isles, in the
Netherlands, Belgium, north-west Ger-
many, west and central France, northem
Spain and east Portugal (Summerfield,
1974). In the Faroe Islands, N. ossifragum
is very common except on the islands Stóra
Dímun, Lítla Dímun, Koltur and Mykines
where it has not been found (Hansen,
1966). It is a lowland plant. This became
clear from the botanical mapping which the
University of Copenhagen performed in
1960-61 (Hansen, 1966). N. ossifragum
was found in 92% of 135 investigated lo-
calities below 300 m above sea level (a.s.l.),
in 56% of the localities at 300-600 m a.s.l.,
and in none the zone above 600 m a.s.l.
(Hansen, 1966). Above 300 m a.s.l. its
growt is scattered and does not cover exten-
sive areas as it does in the lowland. It oc-
curs on shallow, peaty soils and pools. It
flowers in late July and fraits in September.
Large areas are coloured yellow at the
flowering time.
The aetiology of the disease is not fully
known (Fláøyen, 1993). Steroidal saponins
from the plant have been suggested to be
the actual toxins (Ender, 1955), but results
from dosing experiments in lambs suggest
that the saponins alone may not be respon-
sible (Fláøyen etal., 1991b).
Epidemiology
The condition is typically a disease of
lambs. About 20 lambs, out of a total
population of 70,000 sheep, are reported to
become photosensitized every year. Most
of these cases occur in the period between
25 June and 10 August.
Fig. l.
Lamb photosensitized after ingestion of Narthecium
ossifragum showing typical clinical signs.
Ordinarily a few cases (<5 cases) of pho-
tosensitization in adult sheep are reported
to occur in late April and early May. At that
time the N. ossifragum is sprouting and
there are few other green plants available as
feed.
Cases are widely spread, but mostly re-
ported to occur on Eysturoy between Norð-
skála and Eiði and on Streymoy between
Hvalvík and Tjømuvík. The disease occurs
mainly in sheep grazing lowland pastures.
A daily surveilance of the grazing animals
is normally not performed in the Faroe Is-
lands, and unreported cases do probably
occur.