Effect of Inbreeding on Age at First Calving and Calving Interval in Holstein Cows in Isfahan Province

This study was carried out to estimate inbreeding coefficient and its effect on age at first calving and calving interval in dairy cattle herds in Isfahan province.  Pedigree information from 86,481 cattle during 1964 to 2010 was used. The average of inbreeding coefficient in whole population was about 2.33%, minimum= 0% and maximum=31.30%. However, in the inbred animals (57234 animals) inbreeding coefficient was estimated about 3.57%. The inbreeding coefficients of the females and males in were different and around 2.33 and 4.20%, respectively. In this study, effect of inbreeding for age at first calving was based on using 31977 records from primiparous cows, and for calving interval 36982 records of multiparous cows. According to an animal model and using inbreeding rate as a covariate effect, average of regression coefficient for age at first calving and calving interval were estimated for every 1% increasing in inbreeding as 0.589±0.21 and 1.08±0.15, respectively.

Key words: Inbreeding coefficient, Age at first calving, Calving interval, Holstein cows