Íslenskar landbúnaðarrannsóknir - 01.09.1974, Page 12

10 ÍSLENSKAR LANDBÚNAÐARRANNSÓKNIR
smaller importance and factors 2 and 3 be-
come more important.
Finally there is a drop in number of eggs
in late May or early June. The reasons for
this are somewhat obscure. A possible ex-
planation is that the egg laying of the adult
nematodes is simply decreasing after spring
rise. But there could also be an immune
response involved, a sort of „self cure",
stimulated by the great infection in the
spring. Such an immune response could di-
minish the egg laying of the adult worms
or even expel them.
In rams and barren ewes, spring rise starts
at the same time and reaches a height similar
to that of lambing ewes. But most often it
seems to be of shorter duration (Fig. 5, 12
and 13). That lambing has an effect on
spring rise is indicated in a ewe lambing a
month earlier than the others (Fig. 5). Here
spring rise starts earlier too.
Figures 4 and 5 seem to indicate that the
first year sheep have fewer eggs of „other
strongyles" than adult sheep which could
mean a smaller worm burden. First year
sheep, however, carry many more worms of
Nematodirus spp. than adult sheep (see Ia-
Fig. 6. Eggs of Nematodirus spp. in faeces of
lambs (age 4—7 months) (Group IV).
ter) so the total burden of gastrointestinal
nematodes is probably higher in first year
sheep.
No resistance can be seen against „other
strongyles" as a whole when lambs and adults
are compared. However, this dœs not ex-
clude the possibility that resistance is devel-
oped against particular species of „other
strongyles".
A hypothesis concerning the variation in
the number of eggs of „other strongyles" in
relation to the age of the sheep and time of
year is illustrated in Fig. 16.
Nematodirus spp.
Two species of Nematodirus have been found
in Iceland, N. filicollis and N. spathiger. The
eggs of these two species were counted to-
gether, but N. filicollis was predominant.
As can be seen in Fig. 6 and 7 the number
•<
Adult sheep
•> Females.
a Male

------------------!------------------------_ 1 -----------------------------------------------------1----------------------_ -----------------------------í
1371
1S72
Fig. 7. Eggs of Nematodirus spp. in faeces of lambs (age 6 months — 114 year) and adult sheep
(older than 2 years) (Group I).