Genetic evaluation of calving ease in Spanish Holstein population

Calving ease is a trait which has incidence on the profitability of dairy herds. In the Basque country, a region of the north of Spain, calving ease data collection is being done since 1992 and a genetic evaluation of sires appears as a demand of dairy farmers in order to reduce the frequency of calving problems. The establishment of a routine genetic evaluation requires an initial study about which methodology should be chosen. Linear and threshold methodologies with a sire model have been applied to the same data. Estimates of heritability are 0.152, for the threshold model, and 0.028, for the linear model. This last result is lower than those observed by other authors using linear methodology. Pearson correlation (0.87) and Spearman correlation (0.66) between breeding values estimated with both methods are small. Spearman correlation reflects that rankings are quite different. For publication of proofs, estimated breeding values based on threshold sire model are expressed in standard deviation units and a minimum of 50 data per sire are required. Further research will focus on the following issues: improvement of the evaluation model, including in it a maternal genetic effect; implementation of an animal model; study of the influence of calving ease on days open; determination of relationships of calving ease with type traits and analysis of economic impact of calving ease in dairy herds.