Genetic analysis of productive life in Holstein cattle in Mexico

Methodology survival analysis model with Weibull proportional hazards was used to study Holstein cattle duration of functional productive life (FPL) in Mexico, using a model sire-maternal grandsire with Survival Kit V3.12 software. The FPL was calculated as the number of days between the date of first calving and the date of culling or censored, with a maximum credit of 305 d per lactation. The FPL was defined as the length of time between first calving and date of culling or death and a maximum of 305 d lactation. The data analyzed were obtained from the Holstein Association of Mexico. The final file consisted of 36,507 records for FPL of cows that calved for the first time between 1995 and 2008. The model included baseline hazard function of Weibull and the following fixed effects: age at first calving, lactation number by stage of lactation with cuts 29, 249 y 305 and standardized production level, with 10 classes with changes in each lactation period included as dependent variables and random effects of herd-year of calving and genetic effects of sire and maternal grandsire. Percentage of censored data was 25.54 %. All analyzed fixed effects were significant (P<0.0001) and had a significant risk of animal culling influence. The heritability calculated logarithmic, original, effective and equivalent scales were 0.08, 0.13, 0.12 and 0.10 respectively, indicating that this character can effectively integrate breeding programs as has been done in other locations of Holstein cattle.