Connectedness in the French Holstein cattle population

An analysis of connectedness in the French Holstein cattle population was c arried out. This study was motivated by the fact that artificial inseminati on (AI) bulls are evaluated at the national level, whereas they are usually progeny tested only in the region of their AI stud. Connectedness among AI studs was measured by the generalised coefficient of determination (CD) of contrasts between mean breeding values of bulls from the different AI stud s. Four connectedness components were distinguished. The relative influence of each component was assessed through the increase in prediction error va riance (PEV) of the contrasts after this information was discarded. CDs of contrasts were always higher than 0.80. Therefore, connectedness level amon g AI studs was high and provided an accurate national genetic evaluation. O ut of the different components of connectedness, withdrawing of proven bull connection data caused the greatest increase in PEV (+47.5 %) primarily du e to the change in the connecting structure of the data. Genetic relationsh ips among bulls were the next important source of information. In contrast, contributions from the planned use of the bulls progeny tested were quanti tatively limited (8 % increase in PEV) and foreign semen had a minor contri bution (2 % increase in PEV). However, in spite of its limited quantitative impact compared to the other components, planned sampling bull connectedne ss is recommended because it provides high quality data for model validatio n and bias investigations. (C) Inra/Elsevier, Paris.