Abstract
A study of the association between various factors and average herd milk yield in Norwegian Red dairy cattle in Norway was performed on data from over 15 000 herds. The data were analysed by the least-squares method. The results can be summarised as follows: 1. (1) About 30% of the total variance in average herd milk yield can be described by the factors included in the present analysis. If information about the concentrates used in the herds is included, close to 60% of the total variation can be accounted for. However, this is an overestimation, since there is an automatic correlation between average milk yield and concentrates fed. 2. (2) The two factors that by themselves describe the largest part of the variance in average herd milk yield are index of the cows culled in the year (11.1%), and the average heart girth in the herd (9.3%). 3. (3) The index of the sires of the cows in the herd described 5.9% of the variation in average herd milk yield. This is an estimate of the genetic component of the between-herd variance. 4. (4) No disease accounted for a large part of the total variance in average herd milk yield.
Published Version
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