Íslenskar landbúnaðarrannsóknir - 01.03.1971, Side 13

SAMANBURÐUR Á AFURÐAGETU 1 1
level. Further the fecundity ol the two year old ewes was directly influenced
bv the degree of North-East blood of the crosses. The twinning rate of ewes
with less than 50% North-East blood being 39.8% but 55.1% of those with
more than 50% North-East bloocf, this difference being significant at the
99.5% level. rI'he fecundity of the two year old ewes of the Fx and F2 and
later generations did not differ significantly inter se, indicating no hybrid
vigour, but was intermediate between those with less than and more than 50%
North-East blood.
No significant clifference in milk yield was observed between the purebred
North-West hornecl strain and the various crosses.
Comparision between ewes born 1957 to 1967 of the polled and horned
North-West strain showed no significant ditference in fecundity while the ewes
of the horned strain had higher points for milk yield than those of the polled
strain, both at two and three years of age and significantly so at the latter age,
contrary to what was the case with ewes of tliese strains born in 1951. This
shows that selection for breed improvement has been much rnore effective
within the horned than the pollecl strain.