Heritability of Fat Yields in Herds with Different Production Levels

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Abstract
Intra-herd-sire heritability estimates were computed to examine the relationship between these values and the herd level of fat yield for 1825 Guernsey, 5451 Holstein and 3465 Jersey daughter-dam pairs. Phenotypic and additively genetic variances showed a definite increase as the mean fat production for the herd increased, and in the Jersey data the correlation between mean fat yield for the herd and intra-herd-year variance was 0.46 [plus or minus] .05. The coefficient of variation, however, declined for the higher herd levels. There was no significant relationship between heritability values and production levels for the groups of herds in any of the breeds. Heritability estimates obtained by pooling the results from each breed were: Guernsey, 0.21 1.06; Holstein, 0.22 [plus or minus] .04; and Jersey, 0.24 [plus or minus] .05. These results do not indicate the need for using different heritability values to predict progress from selection, or to develop selection procedures for herds with different production levels.