Ársrit Ræktunarfélags Norðurlands - 01.01.1967, Blaðsíða 46

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Summary.
1. This article deals with the analysis o£ dairy cow yields (amount of
milk and butterfat percentage) compared with different time of cal-
ving.
The data used were taken from records of two dairy-breeding socie-
ties in Eyjafjörður Iceland.
2. The highest yielding cows calves in Dec., Jan. and Feb. but the
lowest yielding calved in June, July and August. The difference amoun-
ted to ca. 1000 kg milk.
3. The time of calving did not affect the butterfat percentage.
4. There is no considerable difference between highest and lowest
daily yields and the difference in total milk yield during one year is
due to the fact that persistency of lactation is higher with winther-
calvers compared to sommercalvers.
5. The time of calving has changed considerably within the last de-
cades. Now about 37% of the cowes calve in Okt.—March but fifty
years ago 80% of the cowes calved during the same period.
6. The reason for this yield difference cannot possibly be due to ge-
netic differences between the cows. The difference rather depends on
a widely different management level.