Íslenskar landbúnaðarrannsóknir - 01.09.1974, Page 13

SHEEP PARASITES IN ICELAND 11
of Nematodirus eggs was for the most part
much smaller than the number of eggs of
„other strongyles". However the magnitude
of the Nematodirus infection should not be
underestimated because it has been shown
that the rate of Nematodirus egg-production
is approx. 3.5 —100 times smaller than for
the „other strongyles" (Kates 1947, Peters
et al. 1941). This should be kept in mind
when comparing egg-counts of the two
groups.
Because of the low number of Nemato-
dirus eggs it is difficult to interpret the re-
sults. It is not unlikely, however, that the
variation in the number of Nematodirus eggs
is in many ways similar to that of „other
strongyles". Yet there are several differences.
Firstly, no Nematodirus eggs were found
in lambs up to 1 '/2 months of age (Group
X, compare with Fig. 3). But Nematodirus
eggs were found in 2 month old lambs.
Secondly, as Fig. 6 and 7 clearly indicate,
Nematodiriasis is primarily a lamb disease,
and sheep seem to develop considerable resi-
stance to Nematodirus. This resistance seems
to be almost fully developed at one year of
age although sheep never seem to become
completely immune.
A hypothesis concerning the variation in
the number of eggs of Nematodirus spp. in
relation to the age of sheep and time of year
is illustrated in Fig. 16.
LUNG NEMATODES
Three species of lung nematodes have been
found in Icelandic sheep, Muellerius capil-
laris, Dictyocaulus filaria and Protostrongylus
rufescens.
In the experimental group only the first
two species were found.
Larvoepr.g Group IV.
faeces
Lambs born May 1972
■>Fema!es
-txr
o
1972
-ít-td'
100
Lambs born May 1972. GroupV.
S>Females
7
Fig. 8. Larvae of Muellerius capillaris in faeces of
lambs (age 4—1 months) (Groups IV and V).
Muellerius capillaris.
No larvae were found in lambs up to the
age of IV2 months (Group X). From the
age of IVi months the lambs were not stud-
ied because they were on the mountain
pastures, but larvae were found in 4 month
old lambs.
The number of larvae in sheep 4 months
old to 1V2 years shows great individual varia-
tion (Fig. 8 and 9). In some, the number is
very high but in others it is almost nil. It
appears that the lambs become infested with
M. capillaris at different age. A difference in
the grazing habits of the sheep could be the
explanation. M. capillaris is the only sheep
nematode present in this smdy with an inter-
mediate host (several species of snails and
slugs). Miiellenus infection therefore proba-
bly occurs primarily in damper areas, whereas
infections of other sheep nematodes are prob-
ably more equally spread throughout the
grazing areas. Moreover, the probability of
infection is greater during the latter parts of
the summer, when the snails are more abun-
dant and possibly more highly infected with
larvae.
Most adult sheep in this investigation
(Fig. 10) have an average of 50—100 larvae
pr g faeces, but the variation between indi-
vidual measurements can be quite great.