Cluster analysis on across-country genetic correlations for overall type traits and body condition score of Holstein bulls

The aim of the study is to examine the progress in trait harmonization among member countries participating in the International Bull Evaluation Service Organization (Interbull) for overall conformation score (OCS), overall udder score (OUS), overall feet and legs (OFL), and body condition score (BCS) of Holstein bulls. Input values for the cluster analysis were across-country genetic correlations estimated among 8 countries from 2001 to 2011 for overall type traits and among 12 countries from 2009 to 2011 for BCS. Changes in evaluation procedure and trait definition affected the clustering of countries. For OCS, the evolution was clear, particularly for Australia; the genetic correlations between this country and the majority of other members decreased during the years. Other changes in clustering were due to modifications in trait definitions introduced by France (2004), Germany (2007) and United Kingdom–Ireland (2005, 2008 and 2011). The genetic correlations for OUS were generally higher than those for OCS, and changes in clustering were less pronounced: the structure of clusters remained unchanged from 2004 to 2007. For OFL, Australia was even more distant than for the other two composite traits, probably due to the use of ‘‘side view foot diagonal’’ as best predictor of OFL. The changes in trait definition introduced by France Black and White Holstein (2001) and Italy (2003 and 2007) entailed modifications in the structure of dendrograms. The cluster analysis well depicts the difference among countries that sent information on BCS to Interbull and countries that sent angularity as predictor of BCS, as they were grouped in two distinct clusters and the correlations between them were negative. Major effort is needed to harmonize the traits among countries.