عنوان مقاله [English]
In order to estimate the genetic parameters for days from calving to first service (DFS) in Iranian Holstein cattle by using repeatability, multiple-trait (MT) and random regression (RR) models, 159,482 records of parities 1 to 6 collected during 1981 to 2013 and distributed over 33 large Holstein herds were used. Bayesian information criterion of MT model was lower than other models and Bayesian factor of MT model was significant compared to other models (P< 0.05). Estimates of heritability of DFS with RR model decreased from parity 1 (0.09±0.01) to parity 6 (0.03±0.01). Estimated heritability by MT model decreased from parity 1 (0.08) to parity 5 (0.04) and increased in parity 6 (0.10). The obtained heritability using repeatability model was 0.055±0.01. Genetic correlations between DFS in different parities were reduced continuously with increasing distance between parities in RR and MT models. Overall, the result of this study indicate that multiple trait model performs better than other models in estimation of genetic parameter for DFS.