Fróðskaparrit - 31.12.2000, Page 188

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PARASITES IN SHEEP IN THE FAROEISLANDS
Trichuris ovis
The egg counts are generally low with the
highest peak in spring: 30 epg in lambs and
18 epg in ewes (Fig. 5). These figures are
very low, and infection can not be consid-
ered to be of any hazard to the sheep.
Muellerius capillaris
In general, there seemed to be a slight ten-
dency that a greater proportion of ewes than
lambs was infected. In the autumn when
the lambs were five months old, the results
show that 79% of ewes and 60% of lambs
were infected (Fig. 6). These results indi-
cate that infected sheep do not develop any
significant immunity. The number of lar-
vae per gram of faeces was not counted, but
an estimate was made that showed that
there was a large variation, from zero to
several thousand larvae per gram of fae-
ces.
Dictyocaulus filaria
There was a significant difference between
infected lambs and infected ewes in all sea-
sons, with a greater proportion of lambs in-
fected (Fig. 6). This gives a clear indica-
tion of the development of resistance in
older sheep.
Fasciola hepatica
Fluke faecal egg count in the winter of
1999 showed that 8% of lambs and 12% of
ewes were infected, and in the spring of
1999 that no lamb and 4% of the examined
ewes were infected. The number of eggs
identified were, in all positive samples, less
than one epg. As all sheep were treated
with flukicides in the previous autumn, it
was expected that the infection rate would
be low.
Eimeria spp.
Several species of Eimeria were found in
this study, although no attempt was made to
identify the species. The results showed
that Eimeria spp. were found in significant-
ly greater numbers in lambs five to ten
months old than in ewes older than one
year. Furthermore, the highest mean count
was found in lambs five months old, ex-
ceeding 5,000 oocysts per gram of faeces
(opg), then falling below 400 opg in lambs
eight months old, and then rising to above
700 in the spring, when lambs were 10
months old (Fig. 7). As lambs were not
treated against Eimeria, the drop in opg
from four months to eight months is un-
doubtedly due to increased resistance, and
the small rise in the spring is likely caused
by soil contamination. In order to obtain a
better overview of resistance development,
it will be necessary to obtain samples at
lower ages and at more frequent intervals.
General discussion
Although Fasciola hepatica was consid-
ered to be the main parasite hazard in sheep
before medication was available, it now
seems to be of little importance. In other
countries, Nematodirus battus is demon-
strated to be a serious pathogen of lambs in
the first, mild period after winter. Even
though the study found considerable num-
bers of N. battus, it is hard to conclude,
however, the existence of spring nema-
todiriasis, because of a lack of observations
in that period. Haemonchus contortus was