Íslenskar landbúnaðarrannsóknir - 01.03.1970, Blaðsíða 74

72 ÍSLENZKAR LANDBÚNAÐARRANNSÓKNIR
TABLE 34
Least squares estirnates of effects of colour genotypes of eiues and rams
on fertility. Two year old ewes
Genotype of parent Estimated deviations of
Ewes Rarns
No. of matings Among all White vs. nonwhite No. of matings Among all ' White vs. nonwhite
1. Namber of lambs per ewe lambing.
Overall mean (unadjusted) = 1.229
White 2035 - 0.062 2094 - 0.023
Nonwhite 465 0.062 406 0.023
2. Number of lambs per mating.
Overall mean (unadjusted) = 1.089
A]— 2186 -0.036 1311 - 0.024
ArAr 432 -0.001
AiAj, 1 138 - 0.050 655 - 0.034
White 2324 -0.061 2398 - 0.040
Nonwhite 509 0.086 0.061 435 0.059 0.040
the interaction rnean square remains al-
most constant frorn one analysis to another,
while the error mean square changes radic-
ally with changes in the unadjusted mean,
which is clearly seen in table 32.
It is seen from table 33 that there is a
significant difference between farm-years
with respect to number of lambs per ewe
lambing. This is to be expected, as fertility
traits are known to have a relatively low
heritability and that they are modified con-
siderably by environmental factors.
In order to examine further the possible
causes for the difference in fertility be-
tween white and nonwhite ewes an ana-
lysis was carried out where the effect of
the colour of the sires of the lambs was
entered as a variable. This type of analysis
was applied to both number of lambs per
ewe fambing and number of lambs per
mating. For number of lambs per mat-
ing, ewes which had been mated but
had not given birth to a lamb as a result
of that mating were included in the ana-
fysis. These ewes had either returned to
the ram, aborted or becorne barren. Ewes
wliich had diecl during pregnancy or were
without lambing records were excludecl.
In the analysis on number of lambs per
ewe lambing, which was only carried out
for 2 year olcl ewes, the ewes and rams
were only divided into two groups, i.e.
white and nonwhite. This analysis includes
all nonwhite ewes, irrespective of genotype
and only ewes with known parentage of
lambs, so that the numbers in part 1 of
table 34 are slightly different from those
given in table 32.
In tlie analysis on number of lambs per
mating, the ewes were first divided into 3
groups and tlie rarns into 4 groups as
shown in tables 34 and 36, but subsequent-