Rit Landbúnaðardeildar : B-flokkur - 01.10.1953, Síða 81

./
79
Lot C comprised 29 ewes which reared one lamb each as yearlings and again as 2
yeares old. Lot D consisted of ewes, which reared one lamb each as yearlings and
twins, when 2 years old. In lot E there were 5 ewes which reared one lamb as year-
lings and were barren or lost their lambs at hirtli, when 2 years old.
The mean live-weight of these ewes, when 4 months old (lst October 1948) was
in lot A 41.05 kilos, in lot B 40.73 kilos, in lot C 41.24 kilos, in lot I) 44.10 kilos and
in lot E 39.70 kilos. Analysis of variance showed that the difference in weight between
the lots at this age was not significant. The greater weight of the lambs in lot D than
in the other lots, however, may have some disturbing effects on the final comparison
of that lot with the others as they incidentally were of slightly larger frame. These
64 cwes were all winterfed in one lot hotli in their first and second year and grazed
on the same wild pasture from birth to slaughter. Therefore one is justified to con-
sider that any differences in development of the ewes ]>etween Ihe lots observed, when
killcd at 28 months of age are primarily due to whether the ewes reared lambs or not
as yearlings and again whether they reared singles, twins, or were barren when two
years old. As the standard of feeding and the iive-weight gain of hoth the barren and
the pregnant cwes dealt with in Part II during their first winter was similar to that
of tlie ewes in Part I, one is furthermore justified in considering that any differences
observed at 28 months between lots B and C in Part II are comparable with differences
one could have expected between the ewes in lots A and C of Part I, if they liad
Iived to the age of 28 months and had all reared singles as two years old.
All the data were subjected to analysis of variance. Snedecor’s F-test was used
followed by tlie t-test for significance of difference hctween any two lot means.
Summary of Resuits.
Part I.
1. To study the effects of pregnancy and milk production of ewes, lambing for
the first time when 12 months old, on their growth and development up to 16 months
of age, 43 yearling ewes of the purebred Iceland hreed of sheep were used.
2. These ewes when killed at 16 months of age were divided into 3 lots A, B
and C according to whether they had been barren (lot A), had lost their lambs at birth
(lot B) or had reared their lambs (lot C).
3. Live-weight changes of the ewes in the different lots were studied. From 4
to 11 months (i. e. from lst October to 5th May, 12 days before the first hoggets
were due to lamb) the pregnant ewes (lot B and C) gained on the average 4.04 kilos
more in live-weight than the empty ones (lot A), the latter gaining only 2.86 kilos during
this period. Tlie difference corresponds closelv to tlie expected weight of foetus plus
foetal fluids at tliis stage of pregnancy indicating that pregnancy up to the 120th day
has not had any marked retarding effects on the growth of the mothers. From 4 to 16
monlhs (lst October to 23rd Septemher) the barren ewes (lot A) gained on the average
23.09 kilos in live-weight, those wiiich lost their lambs at birtli (lot B) 21.00 kilos,
wbiie those which reared lambs (lot C) gained only 11.53 kilos. Thc lambs reared hy
the yearling ewes in lot C when killed 4 months old dressed on the avcrage with 15.21
kilos carcass, 1.04 kiios loose fat and 2.92 kilos skin with wool.
4. The difference in mean live-weight between tlic ewes of the three lots at 16
months of age was found to be primarily due to difference in tlie weight of dressed
carcass, loose-fat and pelt. Pregnancy, strain of parturation and suckling of tlie lambs
has therefore liad negligible effects on the growth in weight of the earliest maturing
parts of the body, the iuternal organs, head and feet as a whole.
5. The ewes which reared lambs (lot C) gave 5.22 kilos or 21.3% lighter dressed
carcass than the barren ones (lot A), this difference being highly significant. The
ewes which lost their lambs at birth (lot B) had significantly greater dressed carcass