Estimation of Genetic Parameters and Breeding Values of Milk Traits for Simmental Cattle in Croatia Using a Lactation Animal Model

The objective of this study was to estimate genetic parameters and to predict breeding values for dairy traits in Simmental cattle in Croatia by developing an animal lactation model. Data consisted of 30761 first lactation records of cows born between 1985 and 2001. By including the pedigree there was a total of 48748 animals. The following effects were analyzed: age, season and year at first calving, days open, breeding organization, farm, animal, and genetic group. Adequacy of the models was tested by using F tests for fixed effects, and REML functions and ‘Mendelian sampling’ for the whole models. The best fit model was determined to have the following effects: age at first calving, days open, year x season interaction and breeding organization x year interaction as fixed, and animal and farm x year as random effects. By including genetic group the model was further improved. From this model, the following heritabilites were estimated: 0.34 ± 0.02, 0.30 ± 0.02, 0.29 ± 0.03 for milk, milk fat and protein yield, respectively. Further, phenotypic and genetic trends were analyzed. The genetic gain in milk traits has been low so far, but by using an appropriate animal model, the breeding value prediction is expected to be improved in terms of accuracy and precision.