Genetic variance components for female fertility in Iranian Holstein cows

Linear and threshold animal models were used to estimate genetic parameters for reproductive traits in Iranian Holstein cows. Reproductive traits included: days from calving to first service (DFS), number of inseminations to conception (INS), calving interval (CI), days open (DO), and interval between first and last insemination (IFL), pregnancy rate (PR), and success to first insemination (SF). A total of 72,124 records in parity 1 to 6 from 27,113 cows from 1981 to 2007 were used. Estimated heritabilities for reproductive traits were low (below 0.1); SF (0.029) had the lowest and DO and PR had the highest (0.076) heritability. Heritabilities obtained for interval traits were higher than those for categorical and binary traits. Strong genetic correlations were estimated between fertility traits. The results from current study show that fertility is a complex trait and several measurements related to fertility should be combined in a fertility index for selection purposes.