Rit Landbúnaðardeildar : B-flokkur - 01.10.1953, Blaðsíða 80

Rit Landbúnaðardeildar : B-flokkur - 01.10.1953, Blaðsíða 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.
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