كليدواژه :
فاصله زايش , سن زايش , هلشتاين ايران , پارامترهاي ژنتيكي
چكيده لاتين :
This study was conducted using production and reproduction records of Holstein cattle of Iran collected by Animal Breeding Center of Iran, during 1997 to 2007. The dataset consisted of 213402 records of lactation 1 to 4. The traits included in the analyses were milk and fat yield, calving interval, dry days and age at first calving. Variance as well as covariance components, genetic and phenotypic parameters were estimated using Restricted Maximum Likelihood as based on single and multiple trait analyses and through ASREML software. In single trait analysis, estimated heritabilities of milk yield were in the range of 0.14 to 0.25, fat yield from 0.08 to 0.19, calving interval from 0.02 to 0.04, age at first calving 0.14 and dry days 0.05 for lactation 1 to 4. There were no significant differences observed between estimates of heritabilities from single and two trait analyses. Genetic and phenotypic correlation between production and reproduction traits, were positive, with unfavorable Genetic correlations higher in magnitude than the phenotypic correlations. Genetic correlation of milk yield of first lactation (with calving interval and age at first calving) were 0.52 and 0.21, respectively. Genetic correlations of milk and fat yield (with calving interval of lactations 1 to 4) were 0.52, 0.70, 0.63, 0.56 and 0.16, 0.56, 0.33, 0.44, respectively.
