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Data related to Holstein dairy cattle production and reproduction traits, collected during
years 1983 to 1998 by the Animal Breeding Center, of Iran, were employed in this research to
estimate variance components and genetic parameters. Six climate regions; dry, semi-dry,
Mediterranean, semi-humid, humid, and very humid, were defined based on advanced
Dumaraton method. Variance and covariance components for milk and fat yield, fat percent,
calving interval, and open days were estimated applying single and multivariate animal models
on data of common bulls daughters in defined regions. Heritability of milk and fat yield for
dried, semi-dried, Mediterranean, humid, semi-humid, and very humid were estimated as
0.29±0.07 & 0.29±0.06, 0.29±0.09 & 0.23±0.09, 0.27±0.08 & 0.22±0.06, 0.25±0.04 &
0.18±0.04, 0.25±0.0 & 0.12±0.06, 0.26±0.08 & 0.24±0.09 and for fat percent 0.18±.0.8,
0.16±0.07, 0.12±0.08, 0.24±.0.4, 0.16±0.06 and 0.12±0.09, respectively. Estimated heritability
for calving interval and open days were 0.098±0.005 & 0.09±0.005, 0.02±.0002 & 0.02±0.002,
0.025±.002 & 0.025±0.002, 0.01±0.004 & 0.01±0.004, 0.02±0.006 & 0.02±0.006, 0.03±0.009 &
0.03±0.009, respectively. The genetic trends for milk yield in the regions were estimated 88.63,
26.48, 2.82, 14.97, 41.21 and -16.85 kg/year, respectively. Genetic correlation for milk yield, fat
yield, and fat percent among different regions ranged from 0.70 to 0.95, 0.73 to 0.96, and 0.80
to 0.98, respectively, and for reproduction traits close to zero. Differences in genetic correlations
of traits among different regions as well as rank of the common bulls, indicated that genotypes
have performed differently in different regions due to effect of genotype-environment
interaction.