EFFECT OF VARIANCE OF INTERACTION EFFECTS OF SIRE AND HERD ON SELECTION FOR MILK AND FAT YIELD

The animal model for genetic evaluations of dairy cattle by the USDA c urrently 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 eith er the 14% or the actual estimate from 20 samples of records from herd s 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 a verage EBV of the bulls and cows selected based on 14% of the total va riance were only slightly less than for those selected on 2%. This pil ot research suggests that further study of the national data be done t o establish the appropriate proportion of variance from interaction ef fects of sire and herd to use with national evaluations. Kinds of eval uations of bulls and ages of cows and bulls should be considered.