Journal of Dairy Science, Vol 79, Issue 1 140-144, Copyright ©
1996 by American Dairy Science Association
Effect of variance of interaction effects of sire and herd on selection for
milk and fat yield
G. Dimov, J. F. Keown, L. D. Van Vleck and H. D. Norman
Department of Animal Science, University of Nebraska,
Lincoln 68583-0908, USA.
The animal model for genetic evaluations of dairy cattle by the USDA
currently includes a term for interaction effects of sire and herd.
The relative magnitude of the variance of that effect was established
in the 1960s as 14% of the total variance, but recent research has
shown that the proportion is 2% or less. This report compared EBV
using either the 14% or the actual estimate from 20 samples of
records from herds in California, New York, and Pennsylvania. From 6
to 22% of bulls or cows selected for milk and fat yields based on
evaluation with 14% of the total variance would not be selected using
the sample estimates, depending on selection intensity, region, and
whether only first or up to three lactations were used in the
evaluations. Nevertheless, the average EBV of the bulls and cows
selected based on 14% of the total variance were only slightly less
than for those selected on 2%. This pilot research suggests that
further study of the national data be done to establish the
appropriate proportion of variance from interaction effects of sire
and herd to use with national evaluations. Kinds of evaluations of
bulls and ages of cows and bulls should be considered.
