Rit Landbúnaðardeildar : B-flokkur - 01.10.1953, Page 80

78
feeding ceased just in the beginning of the lambing season. In the end of June the
ewes were shorn and immediately after driven with their lambs to common wild
mountain grazings and left there to forage for themselves until the 20th of September
each year, when they were gathered and driven to the farm. On 24th September 1950
all the ewes and their lambs were killed without heing fattened on cultivated land
or concentrates prior to slaughter.
All the animals used in the investigation were weighed 3 times a year: lst Octo-
ber, lst February and 5th May and finally on 23rd September, the day before they
were killed.
At slaughter tiie dressed cold carcass weight of eacli ewe, without head, feet,
kidneys and kidney fat was recorded. The pelt (skin with wool) as well as the kidney
and caul fat of each ewe were also weighed. The left fore cannon bone (metacarpal)
of each ewe was dissected out immediately after slaugliter and its fresh weight, length
and minimum circumference recorded. Several external measurements were taken on
each carcass suspended from a gamble of constant width. Subsequently the carcass
was divided into two parts by a vertical cut through the flank to the anterior edge
of the last rih on each side and these cuts extended along the curve of the ribs to the
vertebral column, where the latter was severed. Various measurements were then
taken on the anterior surface of this crosssection of the carcass, illustrated in Text-
fig. 1, page 7. Ali but two of the carcass measurements taken in this study are tlie
same as those used and described by Pálsson (1939, pp. 551—3), Wallace (1948, p. 249)
and Pálsson and Vergés (1952, p. 7); the same lettering is retained. Text-fig. 1 illu-
strates the position of the measurements on the carcass and what measurements each
letter indicates. The two additional measurements taken were the narrowest width
of chest behind the shoulders, W, taken by sliding callipers and the minimum circum-
ference of lieartgirth, U, taken willi a linen tape.
Part I deals with the effects of pregnancy and milk production of ewes lambing
at 12 months of age on their growth and development up to the age of 16 months.
For this investigation 43 ewes killed, when 16 months old were available. They were
divided into 3 lots, A, B and C according to whether they had been barren, had lost
their lambs at birth or had suckled their lambs. Lot A consisted of 11 barren ewes
which had not reached sexual maturity, when put to the ram at tlie age of 7 months
or did not conceive when mated. In lot B there were 11 ewes, some of which ahorted
a few days before they were due to lamb, while others lost their lambs at parturation
or a few days later. Lot C consisted of 21 ewes, which suckled their lambs (all singles)
for a period of 4 months, when both ewes and lambs were killed.
The mean live-weight of these ewes, when 4 months old (lst October 1949) was
in lot A 35.86 kilos, in lot B 35.73 kilos and in lot C 38.21 kilos. Analysis of variance
showed that tlie difference in the mean live-weight between the lots at this age was
not significant. The pedigree records showed that individuals of very similar merit
fell into each lot. These 43 ewes were all winterfed in one lot during the winter
1949—’50, and grazed on the same wild pasture from birth to siaughter. There-
fore we are justified to consider that any differences observed in the development
of the ewes in the different lots, when killed at 16 months of age, are primarily the
result of whether the ewes had suckled lambs, lost their offspring at birth or been
barren.
In Part II it is studied to what extent ewes which have been retarded in develop-
ment up to 16 months of age by rearing lambs as yearlings, can make up for this loss
from 16 to 28 months of age. For this study 64 ewes 28 months old were available, 25
of which were barren and 39 suckled lambs as yearlings. At the time of slaugliter
these 64 ewes were divided into 5 lots A, B, C, D and E. Lot A consisted of 10 ewes
which had never reared lambs, i. e. were all barren as yearlings and either lost their
lambs at birth or were barren again when 2 years old. Lot B was made up of 15 ewes
which were barren in their first year and reared one lamb eaclv, when 2 years oid.