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Abstract
Direct longevity EBV of Italian Brown Swiss sires were predicted using a Weibull proportional hazards model. This trait was defined as the risk of culling from first calving. Records from 511,596 Brown Swiss cows with first calving from 1985 to 2005 were used. The model include fixed (age at first calving) and random (sire’s additive genetic) time independent effects, fixed (herd, parity, quantile of mature equivalent deviation from the yearly herd mature equivalent average, and regression on the dynamic herd size) and random (herd-year with log-gamma distribution) time dependent effects. Predicted breeding values for functional longevity, expressed as relative risk ratios, ranged from 0.58 to 1.69. The EBV were standardized with mean 100 and standard deviation 12. EBV were positively submitted to Interbull trend validation procedure in order to assess EBV variation over time and the possibility of including them in the international exchange of bull indexes.