GENETIC PARAMETERS AND TREND OF PRODUCTION AND REPRODUCTION TRAITS IN IRANIAN HOLSTEIN CATTLE

In this study, the genetic and phenotypic trend of milk and fat production traits were estimated form 94121 cows’ first lactation records and that for age at first calving and calving interval traits were estimated from 41900 cows’ reproduction records. Data related to Iranian Holstein dairy cattle from 1995 to 2003. Data were analyzed, using univariate and mulitivariate animal model with genetic group effects. The heritability of milk yield, fat yield and fat percentage, age at first calving and calving interval were 0.29 (±0.01), 0.22 (±0.01), 0.38 (±0.01), 0.055 (±0.01) and 0.034 (±0.005), respectively. The linear regression of average breeding values and phenotypic values of cows for a trait on birth year provided an estimate of genetic and phenotypic trend, respectively. There genetic trend for milk yield, fat yield and Calving Interval were 53.5 kg, 1.07kg and 0.46 day, respectively. Their trend for fat percentage and Age at First Calving were -0.011% and -0.23 day, respectively. There was a positive phenotypic trend for milk yield, fat yield and fat percentage. This trend was negative for Age at First Calving and Calving Interval.