genetic evaluation of age at first calving, open days and milk production of holstein cattle in iran

the objective of this study was to estimate genetic parameters coupled with genetic and phonotypic trends for age at first calving (afc), open days(od) and milk yield(my) of first lactation in iranian holstein cows. records of reproduction and production for genetic evaluation from 1984 to 2005 for afc, od and my were 71736, 20126 and 20126, respectively. single and two-variable animal models were used to estimate genetic parameters by restricted maximum likelihood procedures and wombat software. heritability of afc, od and my was estimated 0.20±0.02 , 0.04±0.01 , 0.47±0.9 respectively. genetic and phonotypic trends of afc were negative so that phenotype and breeding value average had decreased from 1984 to 2005. genetic and phonotypic trends of od and my were positive. the genetic and phonotypic correlations between od and my were +0.23 and +0.07 respectively.