Estimation of Genetic Parameters and Trends for Age at First Calving and Calving Interval in Iranian Holstein Cows

The objective of this study was to estimate genetic parameters coupled with genetic and phonotypic trends for age at first calving (AFC) and first and second calving interval (CI1 and CI2) in Iranian Holstein cows. Records of reproduction from 1983 to 2007 for AFC, CI1 and CI2 were 261116, 163234 and 92661, respectively. Single and two trait animal model was used to estimate genetic parameters by restricted maximum likelihood procedures using Average Information algorithm in ASREML software. Estimates of heritability were 0.19±0.005 for AFC, 0.04±0.003 for CI1, and 0.04±0.004 for CI2. Genetic trends for AFC, CI1 and CI2 were - 0.75±0.11, 0.004±0.02, - 0.02±0.01day per year and phonotypic trends were -2.35±0.38, - 1.13±0.39, - 0.28±0.23 day per year, for AFC, CI1 and CI2, respectively. The genetic, phonotypic and environmental correlations were – 0.049, 0, 0.002 for AFC and CL1; 0.014, - 0.004, -0.004 for AFC and CL2; and 0.877, 0.081, 0.043 for CL1 and CL2, respectively.