Abstract
Selection differentials for sires and dams of bulls taken into AI use in 1970—1977, as well as for sires used in AI, were combined with an estimate of the quality of dams of female replacements to calculate the (predicted) genetic change in milk yield in the Ayrshire breed. In the period the average annual genetic gain was 0.97 % of the mean yield, in the last three years it was c. 1.1 %. The average generation interval was 6.8 years; 8.7 years for the bull sires, 7.4 years for the bull dams and 6.4 years for the cow sires. The bull sires accounted for 42 %, the bull dams for 37 % and the cow sires for only 12% of the total genetic gain. A more rational use of progeny tested and young bulls, combined with a reduction of the generation interval of 15 %, could easily have increased the genetic progress by 20 %.
Highlights
In the past ten years serious efforts have been made in all Scandinavian countries to develop efficient A
Bull sires It seems appropriate to give the results for the three paths of the selection process studied separately
The differentials noted in the present study correspond, on an average, to a selection intensity (i) of about 20 % calculated from: IG rIG ' ff G where I G = 11.47, rIG == 0.9, and aQ —9 %
Summary
In the past ten years serious efforts have been made in all Scandinavian countries to develop efficient A. The main purpose of the present study is to calculate the intensity of selection for milk yield in the period 1970—76 for the Ayrshire sires and dams used in A. X = average of (corrected) progeny tests for milk yield for all bulls in a particular year.
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